Science Readings

Online Science Readings Chapter 1: What is Science Inquiry?

Chapter 1: What is Science Inquiry?

Inquiry based science means active participation in learning about the the world around you. It can range from simple observations to more formal investigations

Read: Science Inquiry

It is an ongoing cycle of "Explore" and Explain" Often it is based on the scientific method which formalizes the inquiry process. Remember that a hypothesis is an educated guess based on an observation. In a more formal investigation the manipulated (or independent) variable is the one that is changed and the responding (or dependent) variable is the one that is measured. Anything that stays the same is a constant (or controlled) variable .

Read: 5 E's of Science

Read: What is the scientific method?

Elementary science generally is broken into three main areas: Life Science, Earth & Space Science, and Physical Science. The process in learning about these areas includes a balance of text-based readings and active investigation. Reading are often in the form of a science textbook covering these three sections with domain vocabulary. Inquiry can range from actively observing all the way to using the scientific method to investigate. The best textbook series include a good balance of both.

Getting equipment and replacing consumables (i.e., vinegar, salt) are an ongoing consideration active science instruction. Storage can be a difficulty to overcome as well. Watching students discovering science is well worth the effort.

Science Inquiry:

The Link to Accessing the General Education Curriculum

What is inquiry?

Inquiry is an interactive process that actively engages students in learning in meaningful ways. The process of

inquiry is characterized by interactive, student-centered activities focused on questioning, exploring, and posing

explanations. The goal of inquiry is to help students gain a better understanding of the world around them through

active engagement in real-life experiences.

How does inquiry compare with the scientific method?

While inquiry can be incorporated into all content areas, it is most commonly implemented in science classrooms.

Why is inquiry important in science classrooms? The process of inquiry not only enhances students’ understanding

of natural phenomena, but also develops students’ science process skills. It is a nonlinear variation of the scientific

method. Composed of the same basic components, both the scientific method and the inquiry process require

students to conduct research investigations by formulating a question, developing a hypothesis, conducting an

experiment, recording data, analyzing data, and drawing conclusions (see Table 1 below).

Table 1

Scientific Method and Inquiry Process

Scientific Method Inquiry Process

Question or problem

Hypothesis

Experiment

Record

Data analysis

Conclusion

Inquiry phase (inquiry or problem)

Data gathering phase I (hypothesis)

Data gathering phase II (data collection

& analysis)

Implementation phase (conclusion &

explanations)

The major difference between the scientific method and the inquiry process is that the inquiry process provides

more opportunities to move within and among the phases of the inquiry (problem-solving process). Students can

enter the inquiry process at any of the four phases. Generally, students new to this process begin at the inquiry

phase (see Figure 1). They use teacher-guided questions and investigation protocols to develop their questions and

inquiries. Students more familiar with the process are able to extend learning by beginning their inquiry at other

phases. For example, these students may begin the process by reviewing data (data gathering phase I)—for

example, a bar chart on weather patterns or population genetics—and then, based on the data, identifying a research

question or inquiry for further investigation (inquiry phase).

The inquiry process has multiple points of entry (as shown in Figure 1). Eventually, however, students will go

through each phase in order to conduct a thorough investigation. At that point, the inquiry process and scientific

method converge.

Page 1 of 10Differentiated Instruction for Science

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Figure 1. Phases of Inquiry

Science teachers generally like the inquiry process because it targets the eight science process skills that all students

are expected to master in science classrooms. These skills include: (a) make observations; (b) conduct experiments;

(c) collaborate with others about investigations; (d) take measurements; (e) sort and classify (i.e., organisms, types

of substances, etc.); (f) compare and contrast; (g) record findings; (h) analyze findings; and (i) share their results

with others (see Table 2). To ensure that students develop these skills, science lessons often focus on a specific

science process skill. For instance, students may spend an entire class period learning to classify different types of

rocks. Another science lesson may require students to analyze a graph depicting monarch butterfly migratory

patterns.

Table 2

Science Process Skills

Science Process Skills

Observe

Experiment

Collaborate

Measure

Sort/Classify

Compare

Record

Analyze & Share

Although each science process skill is often taught separately, students should also be offered opportunities to learn

and apply more than one process skill at a time. The inquiry process provides opportunities for students to develop

and enhance all of their science process skills through a single research investigation.

What does inquiry look like in science classrooms?

Students in inquiry-based classrooms are provided hands-on opportunities to engage in science investigations using

a more holistic variation of the scientific method. With teachers serving as “facilitators of learning,” inquiry-based

science often consists of team projects, collaboration, student-led investigations, and outdoor explorations. Students

raise questions, pose hypotheses, research and experiment, analyze their data, and provide plausible (evidence-

based) explanations.



Because of the importance of the inquiry process, the National Science Education Standards (NSES) recognizes

”science as inquiry” as a critical content standard all students must master before they graduate from high school.

According to the NSES (National Academy Press, 1996), inquiry-based classrooms should include:

A multifaceted activity that involves making observations; posing questions; examining books and other sources of

information to see what is already known; planning investigations; reviewing what is already known in light of

experimental evidence; using tools to gather, analyze, and interpret data; proposing answers, explanations, and

predictions; and communicating the results. Inquiry requires identification of assumptions, use of critical and

logical thinking, and consideration of alternative explanations. (p. 23)

Because they are student driven and interactive, inquiry-based classrooms are generally more active, physically and

intellectually, than traditional science classrooms.

What is the role of science teachers in inquiry-based classrooms?

Teachers serve as “facilitators of learning” in inquiry-based classrooms, guiding students through the inquiry

process. To foster this type of learning environment, teachers use three types of inquiry in science: structured,

guided, and open (see Table 3). There is debate as to which type of inquiry is best. The general consensus is that

any form of inquiry (structured, guided, or open) can be useful to students when taught appropriately and well.

Structured inquiry is the most teacher-centered of the three types of inquiry. This type of inquiry is commonly seen

in science classrooms in the form of laboratory exercises. The teacher provides fairly structured procedures for the

inquiry activity, and students carry out the investigations. Structured inquiry could be described as the most

traditional approach to inquiry.

On the far side of the spectrum is open inquiry. This type of inquiry requires the least amount of teacher

intervention and is student led. Students often work in groups and plan all phases of the investigations. This is the

purest form of inquiry conducted in science classrooms (see Table 3).

Guided inquiry falls in the middle of the inquiry instructional spectrum. This approach is commonly used when

students are asked to make tools or develop a process that results in a desired outcome. For example, a science

teacher gives her seventh grade middle school students materials to create a rocket but no instructions for designing

the rocket. The students must use their own knowledge and creativity to design the rocket so that it will launch

properly, fly a certain distance, and land without becoming disassembled. The teacher provides the problem and

materials and the students develop the rocket using their own scientific process or procedure.

Table 3

Types of Inquiry Used in Science Classrooms

Type of Inquiry Description Example

Structured Teacher gives students problems to

investigate during hands-on activities, as

well as procedures and materials. Students

must determine the outcome.

Laboratory activities with procedures, materials, and

questions specified.

Guided Teacher gives students the problem or

question and materials. Students have to

determine the process and outcome.

Students are given a hard-boiled egg and paper supplies.

Students are asked to create a device using the supplies

that will protect the egg when it is dropped from a

five-story building.

Open Students determine the problem,

investigation, procedure, and outcome.

Students take a field trip to a vegetable garden. Students

are given several minutes to explore the garden.

Working with a partner, students must identify a



researchable problem and conduct an investigation

based on their observations. For example, which

vegetables grow best in shade?

Teachers and classrooms new to inquiry often begin with structured inquiry activities and transition to more open

inquiry activities. Moving gradually from structured classrooms to open-inquiry classroom environments is often

less overwhelming. Radical changes can be frustrating and upsetting to some students, particularly because inquiry-

based classrooms are typically more student centered. Students in inquiry-based settings are more actively involved

in their discovery and subsequently more responsible for their learning. Teachers using inquiry-based instruction

play more of a “facilitator of learning” role than teachers in traditional settings. Teachers and students may need

practice to get comfortable with learning experiences that require less guidance and fewer teacher interventions.

What are some considerations for implementing inquiry in science?

Teachers can foster better experiences with inquiry in various ways and ultimately positively affect students’

science process skills and understanding of science. Whether the inquiry activity is structured, guided, or open,

these suggestions can help alleviate students’ fears about doing inquiry and build their science process skills, as

well as help them learn science concepts.

When implementing inquiry in science, keep the following in mind:

■ Ask open-ended questions

■ Allow wait time after asking questions

■ Avoid telling students what to do

■ Avoid rejecting and/or discouraging student ideas or behaviors

■ Encourage students to find solutions on their own

■ Encourage collaboration among students

■ Maintain high standards and order

■ Develop and use inquiry-based assessments to monitor students’ progress

■ Know that inquiry can be challenging for some students and be prepared to provide more guidance to those

students when signs of frustration appear (Institute for Inquiry, 1995; Washington Virtual Classroom, 2005)

Why is inquiry important for teaching and learning science?

Inquiry allows students to learn and experience science firsthand, by taking on the roles of scientists. Like

scientists, students use the inquiry process to develop explanations from their observations (evidence) by

integrating what they already know with what they have learned. They learn discrete science concepts and skills,

and how to solve problems using practical approaches—the goal of science education.

Incorporating inquiry into science classrooms empowers students. They play an active role in their learning rather

than the passive role commonly seen in traditional science classrooms. This self-empowerment positively affects

students’ perceptions about science. According to the Institute for Inquiry (2005), students doing inquiry-based

science:

■ View themselves as scientists in the process of learning

■ Accept an “invitation to learn” and readily engage in the exploration process



■ Plan and carry out investigations

■ Communicate using a variety of methods

■ Propose explanations and solutions and build a store of concepts

■ Raise questions

■ Use observations

■ Critique their science practices

Opportunities to think and behave as scientists provide relevancy and credibility to students’ understanding of

science. They learn that it is appropriate to ask questions and seek answers. In addition, students learn the

challenges and pitfalls of investigations.

Lastly, positive research findings have provided further reasons for implementing inquiry into science classrooms.

Mattheis and Nakayama (1988) found that inquiry-based programs at the middle school grades have been found to

generally enhance student performance, specifically performance related to science process skills, laboratory skills,

graphing skills, and data interpretation. Another study found that inquiry-based science instruction can be effective

in promoting scientific literacy and a better understanding of science processes in students from diverse

backgrounds (Cuevas, Lee, Hart, & Deaktor, 2005). Ruffin (2003) found increases in science interest and

improvements in the science process skills among middle school students doing inquiry-based science in a

technology-supported learning environment. Numerous other research studies indicate positive outcomes for

inquiry-based science (Krajcik et al., 1998; White & Fredericksen, 1998).

How can Inquiry be Applied for Students with Learning Disabilities?

A learning disability (LD) is usually associated with students who do not develop skills in a way that is

commensurate with their potential (Lyon et al., 2001). LD is not a specific disability itself, but is a general category

of disability composed of disabilities in any combination of the following skills: listening, speaking, basic reading,

reading comprehension, arithmetic calculation, mathematic reasoning, and written expression (Lyon et al., 2001).

Disabilities in the skills mentioned above can affect performance in the science classroom where students are

required to listen, speak, and apply reading, writing, and mathematics skills. Specifically, LD can affect a student’s

experience in a science classroom that uses an inquiry approach.

There is a small body of research on students with LD in an inquiry classroom. A study by Scruggs, Mastropieri,

Bakken, and Brigham (1993) suggests that students with LD who learn through an inquiry-oriented approach,

rather than through a textbook-based approach, perform better on unit tests. Bay, Staver, Bryan, and Hale (1992)

compared the effectiveness of direct instruction and discovery teaching, where students were actively engaged in

gathering data, generating and implementing solutions, and observing their consequences with the science

achievement of students with mild disabilities and students without disabilities. The researchers found that

students’ retention after 2 weeks was higher for those who received discovery instruction. Results also indicated

that students with learning disabilities who received discovery instruction outperformed students with learning

disabilities who received direct instruction. Evidence also exists suggesting that this approach leads to higher

achievement for students with learning disabilities than an activity-based approach alone (Dalton & Morocco,

1997).

Researchers have examined the characteristics of students with learning disabilities, and connections can be made

between these characteristics and strategies that may help students access an inquiry-based curriculum. In addition,

the student-centered nature of inquiry allows teachers the flexibility to tailor instruction to meet the diverse learning

needs that students with LD bring to the classroom. Table 4 helps to make these connections by providing



implications for access to inquiry for students with LD at each phase of inquiry, as well as strategies to support

these students in an inquiry-based classroom. Many of the strategies listed are linked to a resource or Web site that

can provide more information.

Table 4

Strategies to Support Students With Learning Disabilities During Phases of Inquiry

Phase of Inquiry

Implications for Access for Students

With LD Strategies to Support Students with LD

Inquiry Phase

Requires student to consider the

topic at hand and to pose questions

Students with LD may have difficulty

linking new concepts and vocabulary to

familiar ideas,1 which can affect their

ability to understand a new topic and

therefore pose questions about it.


with expressive language,2 which may

affect their ability to articulate questions

or inquiries about a topic. If students

have an LD in written language, they

may have difficulty expressing ideas in

written form.

Abstract concepts may need to be made

more concrete3 for students with LD.

Mnemonics improves memory by linking new

information to current knowledge through visual

and verbal cues. Mnemonics, used in a laboratory

setting, can help students learn vocabulary,4 which

can lead to better comprehension of science topics.

Graphic organizers, which provide a pictorial

representation of concepts, can help students with

LD see the connection among ideas and draw

conclusions that will help them pose questions.

Graphic organizers can also make abstract concepts

more concrete for students.

Peer tutoring can lead to improved academic

achievement in content areas.5

Data Gathering Phase I

(Verification

/Hypothesis)

Requires students to conduct initial

stages of research and exploration

and to propose a working hypothesis


with logical reasoning which can impact

their ability to predict.6

Selective attention difficulties in some

students with LD can lead them to focus

on only one part of a problem,7 which

may affect their ability to see the “big

picture” when proposing hypotheses.

Use graphic organizers to help students with LD

organize steps during initial stages of research, and

to organize initial data collection, helping to

connect ideas so that a hypothesis can be formed.

Consider the use of assistive technology (AT),

which can provide support for students as they

collect and record data and may help them express

their working hypothesis.

Use a “think-pair-share” strategy allowing students

to come up with their own hypothesis, compare

their hypothesis with those of peers, and share a

jointly developed hypothesis.

Grouping strategies can provide appropriate

academic models and support from other students.

Teachers can model and teach metacognitive skills

and demonstrate how to think through a problem.

Allow students to visually represent the problem

and hypothesis.

Ask students questions that activate prior

background knowledge and allow them to make

new connections to concepts that are

already familiar.

Teaching students cognitive strategies, such as note-

taking, outlining, and questioning, may help them

organize data.

Data Gathering Phase II

(Experimentation/ Data Analysis)

Requires students to engage in


selecting, implementing, and adjusting

strategies for problem solving.8

Students with LD should be taught new skills in a

systematic manner that involves continued practice

and teacher guidance11 so that instruction is



intense research and data collection

(observing, measuring), to study the

data, and to analyze the data.


focusing on a task over a sustained

period of time.9

This can affect their

ability to complete an inquiry

investigation during an extended block

of time.


with visual perception and

discrimination, which might lead to

errors while looking at data.10

Students with an LD in mathematics

may needsupport with data analysis and

interpretation.

Selective attention difficulties may

impact a student with LD’s ability to

control variables during an investigation

(for example, identifying all variables

and keeping all but the tested variable

unchanged).

scaffolded.

AT and the use of computer programs can assist

students with organizing and analyzing data and

may also help students who have difficulty with

selective attention.

Teach students to independently check work, ask

for help, as clarifying questions, or redo work if

necessary.12 These skills should be directly taught

and modeled for students with LD.

Teach students note-taking strategies, such as two-

columned notes, that provide ways to record data.

Schedule data collection in several shorter time

blocks rather than one longer time block. This will

give students time to process what they have

already done and allow them to maintain focus on

the task.

Allow students to speak their data collection notes

into a tape recorder rather than writing them down.

Implementation Phase

(Conclusion/

Closure/

Extension)

Requires the student to organize

data and analysis, draw conclusions,

and formulate explanations.


with logical reasoning, which can

impact their ability to infer and problem

solve.13

Students with LD may have a tendency

toward becoming over-reliant on the

opinions of others and reluctant to use

their own judgment,14

which can affect

their ability to draw their own

conclusions, particularly in group work

situations.

Students with LD who have

comprehension difficulties may also

have difficulties constructing

inferences.15

Using hands-on activities during inquiry lessons can

provide positive experiences for students with LD,

leading to increased confidence in their own

ability,16 which may help students feel more

confident about drawing their own conclusions.

Asking students questions that activate related

background knowledge may assist students with

comprehension tasks,17

which may in turn help them

with constructing inferences.

Teachers can model thinking processes for students

to show them how they use data to draw

conclusions.

Offer students a variety of options for their

predictions and conclusions so that they can begin

learning the process by selecting the best choice.

Eventually students will move to creating their own

predictions.

Students may need additional time to examine data

several times and revisit previous ideas or concepts

before drawing conclusions.

Graphic organizers can help students organize data

and provide a visual representation of connections

among ideas.

Conclusion

Incorporating inquiry into science classes takes time and effort, but the rewards are numerous. The inquiry process

is active, engaging, and transferable. Studies have found that not only are students learning more science content

through inquiry, but they are also developing the ability to “study the natural world and propose explanations based

on the evidence derived from their work” through inquiry (NAP, 1996).

Students with LD can be active participants in and benefit from instruction in an inquiry-based classroom as well. It

is essential, however, that these students are provided with direct instruction, classroom supports, and a guided

process that allows them to transfer what they have learned. A variety of research-based instructional strategies can



be used to support the learning needs of students with LD. The Access Center’s Strategies to Provide Access to the

General Education Curriculum provides an in-depth look at research-based strategies that can help support students

with disabilities. These strategies, along with those highlighted in this brief, can help foster success for students

with disabilities in an inquiry-based classroom.

References

American Association for the Advancement of Science. (1993). Benchmark for science literacy. Oxford: Oxford

University Press.

Baker, L. (1982). An evaluation of the role of metacognitive deficits in learning disabilities. Topics in Learning &

Learning Disabilities, 2, 27–35.

Bay, M., Staver, J. R., Bryan, T., & Hale, J. B. (1992). Science instruction for the mildly handicapped: Direct

instruction versus discovery teaching. Journal of Research in Science Teaching, 29, 555–570.

Bell, D. (2002). Making science inclusive: Providing effective learning opportunities for children with learning

difficulties. Support for Learning, 17(4), 156-161.

Billingsley, B., & Wildman, T. (1988). The effects of prereading activities on the comprehension monitoring of

learning disabled adolescents. Learning Disabilities Research, 4, 36–44.

Cohen, P. A., Kulik, J. A., & Kulik, C. C. (1982). Educational outcomes of tutoring: A meta-analysis of findings.

American Educational Research Journal, 19(2), 237–248.

Cook, S. B., Scruggs, T. E., Mastropieri, M. A., & Casto, G. C. (1985). Handicapped students as tutors. Journal of

Special Education, 19, 483–492.

Cuevas, P., Lee, O., Hart, J., Deaktor, R. (2005). Improving science inquiry with elementary students of diverse

backgrounds. Journal of Research in Science Teaching, 42(3), 337–357.

Hardman, F. & Beverton, S. (1993). Co-operative group work and the development of metadiscoursal skills.

Support for Learning, 8(4), 146-150.

Institute for Inquiry. (1995, March–April). Inquiry based science: What does it look like? Connect Magazine, 13.

Retrieved August 19, 2005 from http://www.exploratorium.edu/ifi/resources/classroom/inquiry_based.html

Johnson, D. W., Maruyama, G., Johnson, R., Nelson, D., & Skon, L. (1981). Effects of cooperative, competitive,

and individualistic goal structures on achievement: A meta-analysis. Psychological Bulletin, 89, 47–62.

Krajcik, J., Blumenfeld, P., Marx, R., Bass, K., Fredricks, J., & Soloway, E. (1998). Inquiry in project-based

science classrooms: initial attempts by middle school students. Journal of the Learning Sciences, 7(3/4), 313–350.

Lenz, K., & Schumaker, J. (1999). Adapting language arts, social studies, and science materials for the inclusive

classroom: Volume 3: Grades six through eight. Reston, VA: Council for Exceptional Children.

Lyon, G. R., Fletcher, J. M., Shaywitz, S. E., Shaywitz, B. A., Torgesen, J. K., Wood, F. B., Schulte, A., & Olson,

A. (2001). Rethinking learning disabilities. In C. E. Finn, A. J. Rotherman, & C. R. okansan, Jr., (Eds.), Rethinking

special education for a new century. Washington, DC: The Thomas P. Fordham Foundation.

Mastropieri, M. A., & Scruggs, T. E. (1992). Science for students with disabilities. Review of Educational

Research, 62(4), 377–411.

Mattheis, F. & Nakayama, G. (1988). Effects of a laboratory-centered inquiry program on laboratory skills, science

process skills, and understanding of science knowledge in middle grade students. (ED 307148)

National Academy Press. (1996). National science education standards. Washington, D.C.: National Academy

Press.



National Academy Press. (2000). Inquiry and the national science education standards: A guide for teaching and

learning. Washington, D.C.: National Academy Press.

Rock, E.E. & Fessler, M.A. (1997). The concomitance of learning disabilities and emotional/behavioral

disabilities: A conceptual model. Journal of Learning Disabilities 30(3), 245-263.

Ruffin, M. (2003). The Acquisition of inquiry skills and computer skills by 8th grade urban middle school students

in a technology-supported environment (Doctoral Dissertation, University of Missouri, 2003).

Scruggs, T. E., Mastropieri, M. A., Bakken, J. P., & Brigham, F. J. (1993). Reading versus doing: The relative

effects of textbook-based and inquiry-oriented approaches to science learning in special education classrooms. The

Journal of Special Education, 27, 1–15.

Washington Virtual Classroom. Science inquiry—What is it and how do you do it? Retrieved August 19, 2005,

from http://www.forks.wednet.edu/wvc/cadre/WaterQuality/scienceInq.htm

White, B., & Fredericksen, J. (1998). Inquiry, modeling, and metacognition: Making science accessible to all

students. Cognition & Instruction, 16(1), 3–118.

Wise, B. W., & Snyder, L. (2002). Clinical judgment in identifying and teaching children with language-base

reading difficulties. In R. Bradley, L. Danielson, & D. P. Hallahan, (Eds.), Identification of learning disabilities:

Research to practices. Mahwah, NJ: Lawrence Erlbaum Associates.

1 Bell, 2002

2Rock & Fessler, 1997

3> Lenz & Schumaker, 1999

4Mastropieri & Scruggs, 1992

5 Cohen, Kulik & Kulik, 1982; Cook, Scruggs, Mastropieri, & Casto, 1985; Johnson, Maruyama, Johnson, Nelson & Skon, 1981

6 Bell, 2002

7Hardman et al., 1993

8 Torgesen, 1994

9Bell, 2002

10 Hardman et al., 1993

11Rock et. al, 1997

12 Lenz & Schumaker, 1999

13Bell, 2002

14 Bell, 2002

15Wise & Snyder, 2002

16 Bell, 2002

17 Billingsley & Wildman, 1988

For additional information on this or other topics,

please contact The Access Center at [email protected].

The Access Center: Improving Outcomes for All Students K-8

The Access Center is a cooperative agreement (H326K020003) funded by the U.S. Department of Education, Office of Special Education

Programs, awarded to the American Institutes for Research 1000 Thomas Jefferson St. NW,



Washington, DC 20007

Ph: 202-403-5000 | TTY: 877-334-3499 | Fax: 202-403-5001 |

e-mail: [email protected] website: www.k8accesscenter.org

This report was produced under U.S. Department of Education Cooperative Agreement H326K020003 with the American Institutes for

Research. Jane Hauser served as the project officer. The views expressed herein do not necessarily represent the positions or policies of the

Department of Education. No official endorsement by the U.S. Department of Education of any product, commodity, service or enterprise

mentioned in this publication is intended or should be inferred.

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Constructivism and the Five E's

[ Constructivism | Engage | Explore | Elaborate | Evaluate | Navigate ]

Constructivism. The philosophy about learning, that proposes learners need to build their own understanding of new ideas, has been labeled constructivism. Much

has been researched and written by many eminent leaders in the fields of learning theory and cognition. Scholars such as Jean Piaget, Eleanor Duckworth, George Hein, and Howard Gardener have explored these ideas in-depth. The Biological Science Curriculum Study (BSCS), a team whose Principal Investigator is Roger Bybee developed an instructional model for constructivism, called the "Five Es".

Briefly, this learning approach as it relates to science can be summarized as follows: Learning something new, or attempting to understand something familiar in greater depth, is not a linear process. In trying to make sense of things we use both our prior experience and the first-hand knowledge gained from new explorations. Initially, our curiosity about a science topic is stirred, as we are stimulated by some intriguing phenomena, such as a rainbow, we've noticed. We poke, probe, inquire about and explore this phenomena until it becomes less mysterious. As we begin to investigate new ideas we can put together bits and pieces of prior explorations that seem to fit our understanding of the phenomena under present investigation. In the case of the rainbow, for example, we may realize that there is an association between sunlight and water vapor. Piece by piece we build knowledge. Sometimes when the pieces don't fit together, we must break down old ideas and reconstruct them. (Following a rainbow to find a pot of gold doesn't work easily!) We extend our conceptual understanding through discussions and creative efforts. We validate our theories as we solve problems. In our rainbow example, we may realize that if we position ourselves properly, we can create a rainbow by spraying a water hose in sunlight. The clarity we've gained in understanding a concept gives us the ability to apply this understanding to new situations and new mysteries. It is a continuous and a very individual process. We bring to each learning experience our developmental level, our personal story and our personal style.

It is up to the teacher to facilitate the constructivistic learning process. The structure of the learning environment should promote opportunities and events that encourage and support the building of understanding.

We have used an adaptation of BSCS's model to introduce the pH factor. Our instructional model is called the "Seven Es". Investigations and activities are included under the headings of each E. They are presented to be taught either in sequence or independently, at the teacher's discretion. Each investigation is designed to stand on its own and be introduced when deemed appropriate.

A convenient format to view constructivism has been defined by Biological Science Curriculum Study (BSCS). In this models the process is explained by employing five "E"'s.

Page 1 of 4Miami Museum of Science-The pH Factor/Constructivism and the Five E's

8/24/2012http://www.miamisci.org/ph/lpintro5e.html

They are: Engage, Explore, Explain, Elaborate and Evaluate.

Engage. In the stage Engage, the students first encounter and identify the instructional task. Here they make connections between past and present learning

experiences, lay the organizational ground work for the activities ahead and stimulate their involvement in the anticipation of these activities. Asking a question, defining a problem, showing a surprising event and acting out a problematic situation are all ways to engage the students and focus them on the instructional tasks. If we were to make an analogy to the world of marketing a product, at first we need to grab the customer's attention. We won't have their attention unless they have a need to buy the product. They may be unaware of a need, and in this case we are motivated to create a need.

Explore. In the Exploration stage the students have the opportunity to get directly involved with phenomena and materials. Involving themselves in these activities

they develop a grounding of experience with the phenomenon. As they work together in teams, students build a base of common experience which assists them in the process of sharing and communicating. The teacher acts as a facilitator, providing materials and guiding the students' focus. The students' inquiry process drives the instruction during an exploration.

Explain. The third stage, Explain, is the point at which the learner begins to put the abstract experience through which she/he has gone /into a communicable form.

Language provides motivation for sequencing events into a logical format. Communication occurs between peers, the facilitator, or within the learner himself. Working in groups, learners support each other's understanding as they articulate their observations, ideas, questions and hypotheses. Language provides a tool of communicable labels. These labels, applied to elements of abstract exploration, give the learner a means of sharing these explorations. Explanations from the facilitator can provide names that correspond to historical and standard language, for student findings and events. For example a child, through her exploration, may state they have noticed that a magnet has a tendency to "stick" to a certain metallic object. The facilitator, in her discussion with the child, might at this stage introduce terminology referring to "an attracting force". Introducing labels, after the child has had a direct experience, is far more meaningful than before that experience. The experiential base she has built offers the student an attachment place for the label. Common language enhances the sharing and communication between facilitator and students. The facilitator can determine levels of understanding and possible misconceptions. Created works such as writing, drawing, video, or tape recordings are communications that provide recorded evidence of the learner's development, progress and growth.

Elaborate. In stage four, Elaborate, the students expand on the concepts they have learned, make connections to other related concepts, and apply their understandings

to the world around them. For example, while exploring light phenomena, a learner constructs an understanding of the path light travels through space. Examining a lamp post, she may notice that the shadow of the post changes its location as the day grows later. This observation can lead to further inquiry as to possible connections between the shadow's changing location and the changes in direction of the light source, the Sun. Applications to



real world events, such as where to plant flowers so that they receive sunlight most of the day, or how to prop up a beach umbrella for shade from the Sun, are both extensions and applications of the concept that light travels in a straight path. These connections often lead to further inquiry and new understandings.

Evaluate. Evaluate, the fifth "E", is an on-going diagnostic process that allows the teacher to determine if the learner has attained understanding of concepts and

knowledge. Evaluation and assessment can occur at all points along the continuum of the instructional process. Some of the tools that assist in this diagnostic process are: rubrics (quantified and prioritized outcome expectations) determined hand-in-hand with the lesson design, teacher observation structured by checklists, student interviews, portfolios designed with specific purposes, project and problem-based learning products, and embedded assessments. Concrete evidence of the learning proceed is most valuable in communications between students, teachers, parents and administrators. Displays of attainment and progress enhance understanding for all parties involved in the educational process, and can become jumping off points for further enrichment of the students' education. These evidences of learning serve to guide the teacher in further lesson planning and may signal the need for modification and change of direction. For example, if a teacher perceives clear evidence of misconception, then he/she can revisit the concept to enhance clearer understanding. If the students show profound interest in a branching direction of inquiry, the teacher can consider refocusing the investigation to take advantage of this high level of interest.

Viewing the evaluation process as a continuous one gives the constructivistic philosophy a kind of cyclical structure. The learning process is open-ended and open to change. There is an on going loop where questions lead to answers but more questions and instruction is driven by both predetermined lesson design and the inquiry process.

[ Classroom Use | Why the Seven E's | Constructivism and the Five E's ]

CLICK on one of the Seven E's below to learn more about the rationale behind it.



pH Factor Home

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Steps of the Scientific Method

Key Info

• The scientific method is a way to ask and answer scientific questions by making observations and doing

experiments.

• The steps of the scientific method are to:

◦ Ask a Question

◦ Do Background Research

◦ Construct a Hypothesis

◦ Test Your Hypothesis by Doing an Experiment

◦ Analyze Your Data and Draw a Conclusion

◦ Communicate Your Results

• It is important for your experiment to be a fair test. A "fair test" occurs when you change only one factor

(variable) and keep all other conditions the same.

• While scientists study how nature works, engineers create new things, such as products, websites,

environments, and experiences.

◦ If your project involves creating or inventing something new, your project might better fit the steps of

the Engineering Design Process (http://www.sciencebuddies.org/engineering-design-process/engineering-design-process-

steps.shtml).

◦ If you are not sure if your project is a scientific or engineering project, you should read Comparing the

Engineering Design Process and the Scientific Method (http://www.sciencebuddies.org/engineering-design-

process/engineering-design-compare-scientific-method.shtml).

Overview of the Scientific Method

The scientific method is a process for experimentation that is used to explore observations and answer questions.

Scientists use the scientific method to search for cause and effect relationships in nature. In other words, they

design an experiment so that changes to one item cause something else to vary in a predictable way.

Just as it does for a professional scientist, the scientific method will help you to focus your science fair project

question, construct a hypothesis, design, execute, and evaluate your experiment.

Page 1 of 4Steps of the Scientific Method

8/24/2012http://www.sciencebuddies.org/science-fair-projects/project_scientific_method.shtml

Steps of the Scientific Method Detailed Help for Each Step

Ask a Question: The scientific method starts when you ask a question

about something that you observe: How, What, When, Who, Which,

Why, or Where?

And, in order for the scientific method to answer the question it must be

about something that you can measure, preferably with a number.

Your Question

(http://www.sciencebuddies.org/science-fair-

projects/project_question.shtml)

Do Background Research: Rather than starting from scratch in putting

together a plan for answering your question, you want to be a savvy

scientist using library and Internet research to help you find the best

way to do things and insure that you don't repeat mistakes from the

past.

Background Research Plan


projects/project_background_research_plan.shtml)

Finding Information


projects/project_finding_information.shtml)

Bibliography


projects/project_bibliography.shtml)

Research Paper


projects/project_research_paper.shtml)



Construct a Hypothesis: A hypothesis is an educated guess about

how things work:

"If _____[I do this] _____, then _____[this]_____ will happen."

You must state your hypothesis in a way that you can easily measure,

and of course, your hypothesis should be constructed in a way to help

you answer your original question.

Variables


projects/project_variables.shtml)

Variables for Beginners


projects/project_experiment_fair_test.shtml)

Hypothesis


projects/project_hypothesis.shtml)

Test Your Hypothesis by Doing an Experiment: Your experiment

tests whether your hypothesis is true or false. It is important for your

experiment to be a fair test. You conduct a fair test by making sure that

you change only one factor at a time while keeping all other conditions

the same.

You should also repeat your experiments several times to make sure

that the first results weren't just an accident.

Experimental Procedure


projects/project_experimental_procedure.shtml)

Materials List


projects/project_materials_list.shtml)

Conducting an Experiment


projects/project_experiment.shtml)

Analyze Your Data and Draw a Conclusion: Once your experiment is

complete, you collect your measurements and analyze them to see if

your hypothesis is true or false.

Scientists often find that their hypothesis was false, and in such cases

they will construct a new hypothesis starting the entire process of the

scientific method over again. Even if they find that their hypothesis was

true, they may want to test it again in a new way.

Data Analysis & Graphs


projects/project_data_analysis.shtml)

Conclusions


projects/project_conclusions.shtml)

Communicate Your Results: To complete your science fair project you

will communicate your results to others in a final report and/or a display

board. Professional scientists do almost exactly the same thing by

publishing their final report in a scientific journal or by presenting their

results on a poster at a scientific meeting.

Final Report


projects/project_final_report.shtml)

Abstract


projects/project_abstract.shtml)

Display Board


projects/project_display_board.shtml)



Science Fair Judging


projects/project_judging.shtml)

Even though we show the scientific method as a series of steps, keep in mind that new information or thinking might

cause a scientist to back up and repeat steps at any point during the process. A process like the scientific method

that involves such backing up and repeating is called an iterative process.

Throughout the process of doing your science fair project, you should keep a journal containing all of your important

ideas and information. This journal is called a laboratory notebook (http://www.sciencebuddies.org/science-fair-

projects/printable_project_logbook.pdf ).

You can find this page online at: http://www.sciencebuddies.org/

You may print and distribute up to 200 copies of this document annually, at no charge, for personal and classroom educational use. When printing this document, you may NOT modify it in any way. For any other use, please contact Science Buddies.

Copyright © 2002 - 2012 Science Buddies. All rights reserved. Reproduction of material from this website without written permission is strictly prohibited. Use of this site constitutes acceptance of our Terms and Conditions of Fair Use (http://www.sciencebuddies.org/science-fair-projects/terms_conditions.shtml).



Online Science Readings Chapter 2: Science Instruction

Chapter 2: Science Instruction

It is an ongoing cycle of "Explore" and Explain" This takes the form of observational (the literal) and the explanation (the inferential). Often it is based on the scientific method which formalizes the inquiry process but it can other forms of investigation and conceptual growth. The following readings give a good overview of this and are directly related to three of the assignments in your science journal assignment.

Read: 5 E's of Science

Read: Predict, Observe, Explain

Read: Concept Maps

Elementary science generally is broken into three main areas: Life Science, Earth & Space Science, and Physical Science. The process in learning about these areas includes a balance of text-based readings and active investigation. Reading are often in the form of a science textbook covering these three sections with domain vocabulary. Inquiry can range from actively observing all the way to using the scientific method to investigate. The best textbook series include a good balance of both.

Getting equipment and replacing consumables (i.e., vinegar, salt) are an ongoing consideration active science instruction. Storage can be a difficulty to overcome as well. Watching students discovering science is well worth the effort.

http://www.sciencebuddies.org/science-fair-projects/project_scientific_method.shtml

http://www.sciencebuddies.org/science-fair-projects/project_scientific_method.shtml

Constructivism and the Five E's

[ Constructivism | Engage | Explore | Elaborate | Evaluate | Navigate ]

Constructivism. The philosophy about learning, that proposes learners need to build their own understanding of new ideas, has been labeled constructivism. Much

has been researched and written by many eminent leaders in the fields of learning theory and cognition. Scholars such as Jean Piaget, Eleanor Duckworth, George Hein, and Howard Gardener have explored these ideas in-depth. The Biological Science Curriculum Study (BSCS), a team whose Principal Investigator is Roger Bybee developed an instructional model for constructivism, called the "Five Es".

Briefly, this learning approach as it relates to science can be summarized as follows: Learning something new, or attempting to understand something familiar in greater depth, is not a linear process. In trying to make sense of things we use both our prior experience and the first-hand knowledge gained from new explorations. Initially, our curiosity about a science topic is stirred, as we are stimulated by some intriguing phenomena, such as a rainbow, we've noticed. We poke, probe, inquire about and explore this phenomena until it becomes less mysterious. As we begin to investigate new ideas we can put together bits and pieces of prior explorations that seem to fit our understanding of the phenomena under present investigation. In the case of the rainbow, for example, we may realize that there is an association between sunlight and water vapor. Piece by piece we build knowledge. Sometimes when the pieces don't fit together, we must break down old ideas and reconstruct them. (Following a rainbow to find a pot of gold doesn't work easily!) We extend our conceptual understanding through discussions and creative efforts. We validate our theories as we solve problems. In our rainbow example, we may realize that if we position ourselves properly, we can create a rainbow by spraying a water hose in sunlight. The clarity we've gained in understanding a concept gives us the ability to apply this understanding to new situations and new mysteries. It is a continuous and a very individual process. We bring to each learning experience our developmental level, our personal story and our personal style.

It is up to the teacher to facilitate the constructivistic learning process. The structure of the learning environment should promote opportunities and events that encourage and support the building of understanding.

We have used an adaptation of BSCS's model to introduce the pH factor. Our instructional model is called the "Seven Es". Investigations and activities are included under the headings of each E. They are presented to be taught either in sequence or independently, at the teacher's discretion. Each investigation is designed to stand on its own and be introduced when deemed appropriate.

A convenient format to view constructivism has been defined by Biological Science Curriculum Study (BSCS). In this models the process is explained by employing five "E"'s.



They are: Engage, Explore, Explain, Elaborate and Evaluate.

Engage. In the stage Engage, the students first encounter and identify the instructional task. Here they make connections between past and present learning

experiences, lay the organizational ground work for the activities ahead and stimulate their involvement in the anticipation of these activities. Asking a question, defining a problem, showing a surprising event and acting out a problematic situation are all ways to engage the students and focus them on the instructional tasks. If we were to make an analogy to the world of marketing a product, at first we need to grab the customer's attention. We won't have their attention unless they have a need to buy the product. They may be unaware of a need, and in this case we are motivated to create a need.

Explore. In the Exploration stage the students have the opportunity to get directly involved with phenomena and materials. Involving themselves in these activities

they develop a grounding of experience with the phenomenon. As they work together in teams, students build a base of common experience which assists them in the process of sharing and communicating. The teacher acts as a facilitator, providing materials and guiding the students' focus. The students' inquiry process drives the instruction during an exploration.

Explain. The third stage, Explain, is the point at which the learner begins to put the abstract experience through which she/he has gone /into a communicable form.

Language provides motivation for sequencing events into a logical format. Communication occurs between peers, the facilitator, or within the learner himself. Working in groups, learners support each other's understanding as they articulate their observations, ideas, questions and hypotheses. Language provides a tool of communicable labels. These labels, applied to elements of abstract exploration, give the learner a means of sharing these explorations. Explanations from the facilitator can provide names that correspond to historical and standard language, for student findings and events. For example a child, through her exploration, may state they have noticed that a magnet has a tendency to "stick" to a certain metallic object. The facilitator, in her discussion with the child, might at this stage introduce terminology referring to "an attracting force". Introducing labels, after the child has had a direct experience, is far more meaningful than before that experience. The experiential base she has built offers the student an attachment place for the label. Common language enhances the sharing and communication between facilitator and students. The facilitator can determine levels of understanding and possible misconceptions. Created works such as writing, drawing, video, or tape recordings are communications that provide recorded evidence of the learner's development, progress and growth.

Elaborate. In stage four, Elaborate, the students expand on the concepts they have learned, make connections to other related concepts, and apply their understandings

to the world around them. For example, while exploring light phenomena, a learner constructs an understanding of the path light travels through space. Examining a lamp post, she may notice that the shadow of the post changes its location as the day grows later. This observation can lead to further inquiry as to possible connections between the shadow's changing location and the changes in direction of the light source, the Sun. Applications to



real world events, such as where to plant flowers so that they receive sunlight most of the day, or how to prop up a beach umbrella for shade from the Sun, are both extensions and applications of the concept that light travels in a straight path. These connections often lead to further inquiry and new understandings.

Evaluate. Evaluate, the fifth "E", is an on-going diagnostic process that allows the teacher to determine if the learner has attained understanding of concepts and

knowledge. Evaluation and assessment can occur at all points along the continuum of the instructional process. Some of the tools that assist in this diagnostic process are: rubrics (quantified and prioritized outcome expectations) determined hand-in-hand with the lesson design, teacher observation structured by checklists, student interviews, portfolios designed with specific purposes, project and problem-based learning products, and embedded assessments. Concrete evidence of the learning proceed is most valuable in communications between students, teachers, parents and administrators. Displays of attainment and progress enhance understanding for all parties involved in the educational process, and can become jumping off points for further enrichment of the students' education. These evidences of learning serve to guide the teacher in further lesson planning and may signal the need for modification and change of direction. For example, if a teacher perceives clear evidence of misconception, then he/she can revisit the concept to enhance clearer understanding. If the students show profound interest in a branching direction of inquiry, the teacher can consider refocusing the investigation to take advantage of this high level of interest.

Viewing the evaluation process as a continuous one gives the constructivistic philosophy a kind of cyclical structure. The learning process is open-ended and open to change. There is an on going loop where questions lead to answers but more questions and instruction is driven by both predetermined lesson design and the inquiry process.

[ Classroom Use | Why the Seven E's | Constructivism and the Five E's ]

CLICK on one of the Seven E's below to learn more about the rationale behind it.



pH Factor Home

Teacher's Guide

Excite Explore Explain Museum Menu

Expand Extend Exchange Examine

©2001 Miami Museum of ScienceQuestions or comments about the site? Write to the Webmaster.

You can buy this resource on CD-ROM for use on computers without internet access.Visit our online store for more information!



Novak's cmap home

Concept Maps: What the heck is this?

Excerpted, rearranged (and annotated) from an online manuscript by Joseph D. Novak, Cornell University

original manuscript was revised in 2008-> http://cmap.ihmc.us/Publications/ResearchPapers/TheoryCmaps/TheoryUnderlyingConceptMaps.htm

Concept maps are tools for organizing and representing knowledge. They include concepts, usually enclosed in

circles or boxes of some type, and relationships between concepts or propositions, (indicated by a connecting line and linking word) between two concepts. Linking words on the line specify the relationship between the two concepts. Joe Novak defines "concept" as a perceived regularity in events or objects, or records of events or objects, designated by a label. Think of the concept "Dog" in your mind, what do you see? You might see a prototype shape (head, four legs etc) and typical examples (terrier, collie, sheepdog) and even be able to explain it (give a definition) in words. The label for most concepts is a word, although sometimes we use symbols such as + or %. Propositions are statements about some object or event in the universe, either naturally occurring or constructed. Propositions contain two or more concepts connected with other words to form a meaningful statement. Sometimes these are called semantic units,or units of meaning. Figure 1 shows an example of a concept map that describes the structure of concept maps and illustrates the above characteristics.

There are two features of concept maps that are important in the facilitation of creative thinking: the hierarchical structure that is represented in a good map and the ability to search for and characterize cross-links. In a concept map the concepts should be represented in a hierarchical fashion with the most inclusive, most general concepts at the top of the map and the more specific, less general concepts arranged hierarchically below. The hierarchical structure for a particular domain of knowledge also depends on the context in which that knowledge is being applied or considered. Therefore, it is best to construct concept maps with reference to some particular question we seek to answer or some situation or event that we are trying to understand through the organization of knowledge in the form of a concept map. Another important characteristic of concept maps is the inclusion of "cross-links." These are relationships (propositions =linking lines with linking words) between concepts in different domains of the concept map. Cross-links help us to see how some domains of knowledge represented on the map are related to each other. In the creation of new knowledge, cross-links often represent creative leaps on the part of the knowledge producer. A final features that may be added to concept maps are specific examples or actual images of events or objects that help to clarify the meaning of a given concept.As defined above, concepts and propositons are the building blocks for knowledge in any domain. We can use the analogy that concepts are like the atoms of matter and propositions are like the molecules of matter. There are now about 460,000 words in the English language, and these can be comibined to form an infinite number of propositions; albeit most combinations of words might be nonsense, there is still the possibility of creating an infinite number of valid propositions. We shall never run out of opportunities to create new knowledge! As people create and observe new or exisiting objects or events, we will continue to create new knowledge.

Page 1 of 8Making Concept Maps (Novak)

8/24/2012https://www.msu.edu/~luckie/ctools/

Figure 1 A concept map about concept mapping

Constructing Good Concept Maps

In learning to construct a concept map, it is important to begin with a domain (an area) of knowledge that is very

familiar to the person constructing the map. Since concept map structures are dependent on the context in which they will be used, it is best to identify a segment of a text, a laboratory activity, or a particular problem or question that one is trying to understand. This creates a context that will help to determine the hierarchical structure of the concept map. It is also helpful to select a limited domain of knowledge for the first concept maps. Once a domain has been selected, the next step is to identify the key concepts that apply to this domain. These could be listed, and then from this list a rank order should be established from the most general, most inclusive concept, for this particular problem or situation, to the most specific, least general concept. Although this rank order may be only approximate, it helps to begin the process of map construction.

The next step is to construct a preliminary concept map. This can be done by writing all of the concepts on Post-its, or preferably by using a computer software program. Post-its allow a group to work on a whiteboard or butcher paper and to move concepts around easily This is necessary as one begins to struggle with the process of building a good hierarchical organization. Computer software programs are even better in that they allow moving of concepts together with linking statements and also the moving of groups of concepts and links to restructure the map. They also permit a computer printout, producing a nice product that can be e-mailed or in other ways easily shared with collaborators or pother interested parties.

Figure 2 shows a list of concepts for making a concept map to address the question, "What is a plant?" What is shown is only one of many possible maps. Simple as this map is, it may contain some propositions that are new to the reader. It is important to recognize that a concept map is never finished. After a preliminary map is



constructed, it is always necessary to revise this map. Good maps usually undergo three to many revisions. This is one reason why computer software is helpful. After a preliminary map is constructed, cross-links should be sought. These are links between different domains of knowledge on the map that help to illustrate how these domains are related to one another. Finally, the map should be revised, concepts positioned in ways that lend to clarity, and a "final" map prepared.

Figure 2 Creating a GOOD MAP

It is important to help students recognize that all concepts are in some way related to one another. Therefore, it is necessary to be selective in identifying cross-links, and to be as precise as possible in identifying linking words that connect concepts. In addition, one should avoid "sentences in the boxes" since this usually indicates that a whole subsection of the map could be constructed from the statement in the box. "String maps" or ("Sentence maps") illustrate either poor understanding of the material or an inadequate restructuring of the map. Figure 3shows an example of a string map.

Students often comment that it is hard to add linking words onto their concept map. This is because they only poorly understand the relationship between the concepts and it is the linking words that specify this relationship. Once students begin to focus in on good linking words, and also identification of good cross-links, they can see that every concept could be related to every other concept. This also produces some frustration, and they must choose to identify the most prominent and most useful cross-links. This process involves what Bloom (1956) identified as high levels of cognitive performance, namely evaluation and synthesis of knowledge. Concept mapping is an easy way to achieve very high levels of cognitive performance, when the process is done well. This is one reason concept mapping can be a very powerful evaluation tool.



Figure 3 Creating a "String" or "Sentence" map (NOT A GOOD MAP)

Facilitating Cooperative Learning

Using concept maps in planning a curriculum or instruction on a specific topic helps to make the instruction

"conceptually transparent" to students. Many students have difficulty identifying and constructing powerful concept and propositional frameworks, leading them to see science learning as a blur of myriad facts or equations to be memorized. If concept maps are used in planning instruction and students are required to construct concept maps as they are learning, previously unsuccessful students can become successful in making sense out of science and acquiring a feeling of control over the subject matter (Bascones & Novak, 1985; Novak, 1991; Novak, 1998). There is a growing body of research that shows that when students work in small groups and cooperate in striving to learn subject matter, positive cognitive and affective outcomes result (Johnson et al., 1981). In our work with both teachers and students, small groups working cooperatively to construct concept maps have proven to be useful in many contexts. For example, the concept maps shown in Figure 4 was constructed by faculty working together to plan instruction in veterinary medicine at Cornell University. In my own classes, and in classes taught by my students, small groups of students working collectively to construct concept maps can produce some remarkably good maps. In a variety of educational settings, concept mapping in small groups has served us well in tasks as diverse as understanding ideas in assimilation theory to clarifying job conflicts for conflict resolution in profit and non-profit corporations. Concept maps are now beginning to be used in corporations to help teams clarify and articulate the knowledge needed to solve problems ranging from the design of new products to marketing to administrative problem resolution.



Figure 4 A map created by a collaborative group

Concept Maps for Evaluation

We are now beginning to see in many science textbooks the inclusion of concept mapping as one way to

summarize understandings acquired by students after they study a unit or chapter. Change in school practices is always slow, but it is likely that the use of concept maps in school instruction will increase substantially in the next decade or two. When concept maps are used in instruction, they can also be used for evaluation. There is nothing written in stone that says multiple choice tests must be used from grade school through university, and perhaps in time even national achievement exams will utilize concept mapping as a powerful evaluation tool. This is a chicken-and-egg problem because concept maps cannot be required on national achievement tests, if most students have not been given opportunities to learn to use this knowledge representation tool. On the other hand, if state, regional, and national achievement exams will utilize concept mapping as a powerful evaluation tool. This is a chicken-and-egg problem because concept maps cannot be required on national achievement tests, if most students have not been given opportunities to learn to use this knowledge representation tool. On the other hand, if



state, regional, and national exams would begin to include concept maps as a segment of the exam, there would be a great incentive for teachers to teach students how to use this tool. Hopefully, by the year 2061, this will come to pass.

Origins and Educational Theory of Concept Maps (Joe Novak)

Concept maps were developed in the course of our research program where we sought to follow and understand changes in childrenÕs know ledge of science. This program was based on the learning psychology of David Ausubel (1963, 1968, 1978). The fundamental idea in Ausubel's cognitive psychology is that learning takes place by the assimilation of new concepts and propositions into existing concept propositional frameworks held by the learner. The question sometimes arises as to the origin of the first concepts; these are acquired by children during the ages of birth to three years, when they recognize regularities in the world around them and begin to identify language labels or symbols for these regularities (Macnamara, 1982). This is a phenomenal ability that is part of the evolutionary heritage of all normal human beings. After age 3, new concept and propositional learning is mediated heavily by language, and takes place primarily by a reception learning process where new meanings are obtained by asking questions and getting clarification of relationships between old concepts and propositions and new concepts and propositions. This acquisition is mediated in a very important way when concrete experiences or props are available; hence the importance of "hands-on" activity for science learning with young children, but this is also true with learners of any age and in any subject matter domain. In addition to the distinction between the discovery learning process, where the attributes of concepts are identified autonomously by the learner, and the reception learning process, where attributes of concepts are described using language and transmitted to the learner, Ausubel made the very important distinction between rote learning and meaningful learning. Meaningful learning requires three conditions:

� The material to be learned must be conceptually clear and presented with language and examples relatable to the learner's prior knowledge. Concept maps can be helpful to meet this condition, both by identifying large general concepts prior to instruction in more specific concepts, and by assisting in the sequencing of learning tasks though progressively more explicit knowledge that can be anchored into developing conceptual frameworks.

� The learner must possess relevant prior knowledge. This condition is easily met after age 3 for virtually any domain of subject matter, but it is necessary to be careful and explicit in building concept frameworks if one hopes to present detailed specific knowledge in any field in subsequent lessons. We see, therefore, that conditions (1) and (2) are interrelated and both are important.

� The learner must choose to learn meaningfully. The one condition over which the teacher or mentor has only indirect control is the motivation of students to choose to learn by attempting to incorporate new meanings into their prior knowledge, rather than simply memorizing concept definitions or propositional statements or computational procedures. The control over this choice is primarily in the evaluation strategies used, and typical objective tests seldom require more than rote learning (Holden, 1992). In fact, the worst forms of objective tests, or short-answers tests, require verbatim recall of statements and this may be impeded by meaningful learning where new knowledge is assimilated into existing frameworks, making it difficult to recall specific, verbatim definitions or descriptions. This kind of problem was recognized years ago in Hoffman's (1962), The Tyranny of Testing.

One of the powerful uses of concept maps is not only as a learning tool but also as an evaluation tool, thus encouraging students to use meaningful-mode learning patterns (Novak & Gowin, 1984; Novak, 1990, Mintzes, Wandersee and Novak, 2000). Concept maps are also effective in identifying both valid and invalid ideas held by students. They can be as effective as more time-consuming clinical interviews (Edwards & Fraser, 1983).

Another important advance in our understanding of learning is that the human memory is not a single "vessel" to be filled, but rather a complex set of interrelated memory systems. Figure 5 illustrates the three memory systems of the human mind.



Figure 5 The three memory systems of the human mind

While all memory systems are interdependent (and have information going in both directions), the most critical

memory system for incorporating knowledge into long-term memory is the short-term or "working memory." All incoming information is organized and processed in the working memory by interaction with knowledge in long-term memory. The limiting feature here is that working memory can process only a relatively small number (five to nine) of psychological units at any one moment. This means that relationships among two or three concepts are about the limit of working memory processing capacity. Therefore, to structure large bodies of knowledge requires an orderly sequence of iterations between working memory and long-term memory as new knowledge is being received (Anderson, 1991). We believe one of the reasons concept mapping is so powerful for the facilitation of meaningful learning is that it serves as a kind of template to help to organize knowledge and to structure it, even though the structure must be built up piece by piece with small units of interacting concept and propositional frameworks. Many learners and teachers are surprised to see how this simple tool facilitates meaningful learning and the creation of powerful knowledge frameworks that not only permit utilization of the knowledge in new contexts, but also retention of the knowledge for long periods of time (Novak, 1990; Novak & Wandersee, 1991). There is still relatively little known about memory processes and how knowledge finally gets incorporated into our brain, but it seems evident from diverse sources of research that our brain works to organize knowledge in hierarchical frameworks and that learning approaches that facilitate this process significantly enhance the learning capability of all learners.

While it is true that some students have more difficulty building concept maps and using these, at least early in their experience, this appears to result primarily from years of rote-mode learning practice in school settings rather than as a result of brain structure differences per se. Socalled "learning style" differences are, to a large extent, differences in the patterns of learning that students have employed varying from high commitment to continuous rote-mode learning to almost exclusive commitment to meaningful mode learning. It is not easy to help students in the former condition move to patterns of learning of the latter type. While concept maps can help, students also need to be taught something about brain mechanisms and knowledge organization,and this instruction should accompany the use of concept maps.



References

� Anderson, O. R. (1992). Some interrelationships between constructivist models of learning and current neurobiological theory, with implications for science education. Journal of Research in Science Teaching, 29(10), 1037-1058.

� Ausubel, D. P. (1963). The Psychology of Meaningful Verbal Learning. New York: Grune and Stratton. � Ausubel, D. P. (1968). Educational Psychology: A Cognitive View. New York: Holt, Rinehart and Winston. � Ausubel, D. P., J. D. Novak, and H. Hanesian. (1978). Educational Psychology: A Cognitive View, 2nd ed. New York:

Holt, Rinehart and Winston. Reprinted, New York: Warbel & Peck, 1986. � Bascones, J., & J. D. Novak. (1985). Alternative instructional systems and the development of problem-solving skills in

physics. European Journal of Science Education, 7(3), 253-261. � Bloom, B. S. (1956). Taxonomy of Educational Objectives--The Classification of Educational Goals. New York: David

McKay. � Edwards, J., and K. Fraser. (1983). Concept maps as reflectors of conceptual understanding. Research in Science

Education, 13, 19-26. � Hoffman, B. (1962). The Tyranny of Testing. New York: Corwell-Collier. � Holden, C. (1992). Study flunks science and math tests. Science, 26, 541. � Johnson, D., G. Maruyama, R. Johnson, D. Nelson, and L. Skon. (1981). The effects of cooperative, competitive and

individualistic goal structure on achievement: A meta-analysis. Psychological Bulletin, 89, 47-62. � Macnamara, J. (1982). Names for Things: A Study of Human Learning. Cambridge, MA: M.I.T. Press. � Mintzes, J., Wandersee, J. and Novak, J. (1998) Teaching Science For Understanding. San Diego: Academic Press. � Mintzes, J., Wandersee, J. and Novak, J. (2000) Assessing Science Understanding. San Diego: Academic Press � Novak, J. D. (1977). A Theory of Education. Ithaca, NY: Cornell University Press. � Novak, J. D. (1990). Concept maps and Vee diagrams: Two metacognitive tools for science and mathematics education.

Instructional Science, 19, 29-52. � Novak, J. D. (1991). Clarify with concept maps. The Science Teacher, 58(7):45-49. � Novak, J. D., & D. B. Gowin. (1984). Learning How to Learn. New York and Cambridge, UK: Cambridge University

Press. � Novak, J. D., & D. Musonda. (1991). A twelve-year longitudinal study of science concept learning. American Educational

Research Journal, 28(1), 117-153. � Novak, J. D., & J. Wandersee, 1991. Coeditors, Special Issue on Concept Mapping of Journal of Research in Science

Teaching, 28, 10.



PREDICT, OBSERVE, EXPLAIN (POE)

Chris Joyce (2006)

The POE strategy was developed by White and Gunstone (1992) to uncover individual students’predictions, and their reasons for making these, about a specific event. Reference: White, R. T., & Gunstone, R. F. (1992). Probing Understanding. Great Britain: Falmer Press.

When to use

POE is a strategy often used in science. It works best with demonstrations that allow immediate observations, and suits Physical and Material World contexts. A similar strategy also works well in mathematics, particularly in statistics.

� It can be used for:finding out students' initial ideas;

� providing teachers with information about students’ thinking;� generating discussion;� motivating students to want to explore the concept;� generating investigations.

The theory

Constructivist theories of learning consider that students’ existing understandings should be considered when developing teaching and learning programmes. Events that surprise create conditions where students may be ready to start re-examining their personal theories.

How the strategy works

� Unless students are asked to predict first what will happen, they may not observe carefully.� Writing down their prediction motivates them to want to know the answer.� Asking students to explain the reasons for their predictions gives the teacher indications of their

theories. This can be useful for uncovering misconceptions or developing understandings they have. It can provide information for making decisions about the subsequent learning.

� Explaining and evaluating their predictions and listening to others’ predictions helps students to begin evaluating their own learning and constructing new meanings.

What to do

� Set up a demonstration of an event, related to the focus topic, that may surprise students, and which can be observed.

� Tell the students what you are going to be doing.

Step 1: Predict

� Ask the students to independently write their prediction of what will happen. � Ask them what they think they will see and why they think this.

Page 1 of 5Predict Observe Explain

8/24/2012http://arb.nzcer.org.nz/strategies/poe.php

Step 2: Observe

� Carry out the demonstration.� Allow time to focus on observation.� Ask students to write down what they do observe.

Step 3: Explain

� Ask students to amend or add to their explanation to take account of the observation.� After students have committed their explanations to paper, discuss their ideas together.

To generate your own POEs

Books that contain science “experiments” are often a good source of appropriate activities for adapting to POE, including old teaching resources that promote transmission teaching. They often include an explanation.

A template is provided for teachers to give to students to write on. To adapt the template, save in your own files, and make appropriate changes.

Limitations

� For primary school students, writing the answer can be a barrier to useful communication of ideas. Oral responses need to be managed so other group members do not initially influence students. (Use Think-Pair-Share, for example, before sharing with the whole group.)

� Younger primary students may have difficulty explaining their reasoning.� It is not suitable for all topics, for example, topics that are not "hands-on" or in which it is difficult

to get immediate results (for example, Living World).� If the POE strategy is used often, some demonstrations should be chosen to not give surprising

results, otherwise students start looking for the trick. This may affect the explanations they give.� Some researchers say that students are more likely to learn from observations that confirm their

predictions. This cautions us to be careful that predictions are not wild guesses. A joint conversation about what we might expect to see, and why, based on the underlying science idea, could help avoid this trap.

References:

Palmer, D. (1995). The POE in the primary school: An evaluation. Research in Science Education, 25 (3), 323-332.Hipkins, R., & Kenneally, N. (2003). Using NEMP to inform the teaching of scientific skills. (Pages 50-51).

Adapting the strategy

� Rather than the teacher demonstrating to the whole class, small groups can carry out the activity themselves. It is more difficult for the teacher to monitor the discussion, but does allow for students to observe more closely.

� With some students it may be more appropriate to ask for oral responses, for example, young or ESOL students.

� If the students are unfamiliar with the underlying concept, or are very young, provide options from which they can choose.

� In mathematics the students investigate, rather than observe.

Examples of ARB resources that use the POE strategy



Resources that use the Predict-Observe-Explain (Predict-Investigate-Explain) strategy.



Name: __________________________________________________________________

Description of focus of demonstration(e.g., What will happen when you put an upside down jar over a lighted candle?)

PredictWrite or draw all the things you think you will see.

ExplainWrite the reasons why you think it will happen this way.

ObserveDraw or describe what you did see.

ExplainAdd to or change your ideas about why it happened.



Copyright © 2011 Ministry of Education, Wellington, New Zealand.

New Zealand Council for Educational Research. All rights reserved

Please Note: ARB material may be reproduced for school-based assessment purposes, not for sale or other purposes.

The ARBs Assessment information Support materials Help Contact us Site map

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Chapter 3a: Physical Science, Nature of Matter

Physical science covers a lot of ground so the chapter has been organized into two parts: the nature of matter and force/motion/energy.

On Earth mass and weight are identical although they often measuring using different systems. In the rest of the universe, however, this is not the case. It is important to understand the conceptual difference between the two and how density is related. Note the formula for mass in the reading.

Read: Mass, Weight, Density

The three parts of the atom are protons, electrons, & neutrons. Each has a specific function within the atom and the combinations determine the elements listed on the Periodic Table. When there are uneven combinations they are called ions and isotopes.

Read: Atomic Structure - Protons, Electrons, Neutrons

Matter exists in four basic states: solid, liquid, gas and plasma. Plasma is ionized gas in which is made up of the the same basis atomic structure although it contains electrons which are not bound to the nucleus making it electrically conductive. 99% of all matter in the universe is plasma. An example of man-made plasma is a fluorescent bulb.

Read: Solid, Liquid, Gas

Matter can change form either by physical change or chemical change.

Read: Physical & Chemical Change

Matter can exist as either an element, a compound, or a mixture.

Read: Elements, Compounds, Mixtures

http://astronomyonline.org/Science/MassDensity.asp

http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm

http://www.chem.purdue.edu/gchelp/liquids/character.html

http://chemistry.about.com/od/lecturenotesl3/a/chemphyschanges.htm

http://chemistry.about.com/od/lecturenotesl3/a/chemphyschanges.htm

http://www.chem.purdue.edu/gchelp/atoms/elements.html

A neutron walked into a bar and

asked how much for a drink.

The bartender replied,

"for you, no charge."

-Jaime - Internet Chemistry Jokes

Atomic Structure

An updated version of this lesson is available at Visionlearning: Atomic Theory & Ions & Isotopes

In the last lesson we learned that atoms were particles of elements, substances that could not be broken

down further. In examining atomic structure though, we have to clarify this statement. An atom cannot be

broken down further without changing the chemical nature of the substance. For example, if you have 1 ton,

1 gram or 1 atom of oxygen, all of these units have the same properties. We can break down the atom of

oxygen into smaller particles, however, when we do the atom looses its chemical properties. For example, if

you have 100 watches, or one watch, they all behave like watches and tell time. You can dismantle one of

the watches: take the back off, take the batteries out, peer inside and pull things out. However, now the

watch no longer behaves like a watch. So what does an atom look like inside?

Atoms are made up of 3 types of particles electrons , protons and neutrons . These

particles have different properties. Electrons are tiny, very light particles that have a negative electrical

charge (-). Protons are much larger and heavier than electrons and have the opposite charge, protons have a

positive charge. Neutrons are large and heavy like protons, however neutrons have no electrical charge.

Each atom is made up of a combination of these particles. Let's look at one type of atom:

The atom above, made up of one proton and one electron, is called

hydrogen (the abbreviation for hydrogen is H). The proton and electron

stay together because just like two magnets, the opposite electrical charges

attract each other. What keeps the two from crashing into each other?

The particles in an atom are not still. The electron is constantly spinning

around the center of the atom (called the nucleus). The centrigugal force

of the spinning electron keeps the two particles from coming into contact

with each other much as the earth's rotation keeps it from plunging into the sun. Taking this into

consideration, an atom of hydrogen would look like this:

A Hydrogen Atom

Keep in mind that atoms are extremely small. One hydrogen atom, for example, is approximately 5 x 10-8

mm in diameter. To put that in perspective, this dash - is approximately 1 mm in length, therefore it would

take almost 20 million hydrogen atoms to make a line as long as the dash. In the sub-atomic world, things

often behave a bit strangely. First of all, the electron actually spins very far from the nucleus. If we were to

draw the hydrogen atom above to scale, so that the proton were the size depicted above, the electron would

actually be spinning approximately 0.5 km (or about a quarter of a mile) away from the nucleus. In other

words, if the proton was the size depicted above, the whole atom would be about the size of Giants Stadium.

Another peculiarity of this tiny world is the particles themselves. Protons and neutrons behave like small

particles, sort of like tiny billiard balls. The electron however, has some of the properties of a wave. In other

words, the electron is more similar to a beam of light than it is to a billiard ball. Thus to represent it as a small

particle spinning around a nucleus is slightly misleading. In actuality, the electron is a wave that surrounds the

Atomic Structure http://web.jjay.cuny.edu/~acarpi/NSC/3-atoms.htm

1 of 3 9/18/2012 7:00 PM

nucleus of an atom like a cloud. While this is difficult to imagine, the figure below may help you picture what

this might look like:

Hydrogen: a proton surrounded by an electron cloud

While you should keep in mind that electrons actually form clouds around their nucleii, we will continue to

represent the electron as a spinning particle to keep things simple.

In an electrically neutral atom, the positively charged protons are always balanced by an equal number

of negatively charged electrons. As we have seen, hydrogen is the simplest atom with only one proton and

one electron. Helium is the 2nd simplest atom. It has two protons in its nucleus and two electrons spinning

around the nucleus. With helium though, we have to introduce another particle. Because the 2 protons in the

nucleus have the same charge on them, they would tend to repel each other, and the nucleus would fall apart.

To keep the nucleus from pushing apart, helium has two neutrons in its nucleus. Neutrons have no electrical

charge on them and act as a sort of nuclear glue, holding the protons, and thus the nucleus, together.

A Helium Atom

As you can see, helium is larger than hydrogen. As you add electrons, protons and neutrons, the size of

the atom increases. We can measure an atom's size in two ways: using the atomic number (Z) or using the

atomic mass (A, also known as the mass number). The atomic number describes the number of protons in an

atom. For hydrogen the atomic number, Z, is equal to 1. For helium Z = 2. Since the number of protons

equals the number of electrons in the neutral atom, Z also tells you the number of electrons in the atom. The

atomic mass tells you the number of protons plus neutrons in an atom. Therefore, the atomic mass, A, of

hydrogen is 1. For helium A = 4.

Ions and Isotopes

So far we have only talked about electrically neutral atoms, atoms with no positive or negative charge on

them. Atoms, however, can have electrical charges. Some atoms can either gain or lose electrons (the

number of protons never changes in an atom). If an atom gains electrons, the atom becomes negatively

charged. If the atom loses electrons, the atom becomes positively charged (because the number of positively

charged protons will exceed the number of electrons). An atom that carries an electrical charge is called an

ion. Listed below are three forms of hydrogen; 2 ions and the electrically neutral form.


2 of 3 9/18/2012 7:00 PM

H+ : a positively charged hydrogen ion H : the hydrogen atom H

- : a negatively charged hydrogen ion

Neither the number of protons nor neutrons changes in any of these ions, therefore both the atomic

number and the atomic mass remain the same. While the number of protons for a given atom never changes,

the number of neutrons can change. Two atoms with different numbers of neutrons are called isotopes. For

example, an isotope of hydrogen exists in which the atom contains 1 neutron (commonly called deuterium).

Since the atomic mass is the number of protons plus neutrons, two isotopes of an element will have different

atomic masses (however the atomic number, Z, will remain the same).

Two isotopes of hydrogen

Hydrogen

Atomic Mass = 1

Atomic Number = 1

Deuterium

Atomic Mass = 2

Atomic Number = 1

If you would like to explore the interaction of protons and electrons further, the University of Colorado's

Physics 2000 site has an interesting experiment posted on line. At the Electrical Force page, you can place an

electron next to a proton and see how the electron moves. You can even try to build your own atom (and see

how difficult it is)!

Copyright © 1998-1999, All Rights Reserved, Anthony Carpi


3 of 3 9/18/2012 7:00 PM

Chemical & Physical Changes

Understanding States of Matter

By Anne Marie Helmenstine, Ph.D., About.com Guide

See More About:

• chemical and physical changes

• states of matter

• introductory chemistry

Fire indicates a chemical change.

Christine, www.morguefile.com

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Chemical and physical changes are related to chemical and physical properties.

Chemical Changes

Chemical changes take place on the molecular level. A chemical change produces a new

substance. Examples of chemical changes include combustion (burning), cooking an egg, rusting

of an iron pan, and mixing hydrochloric acid and sodium hydroxide to make salt and water.

Physical Changes

Physical changes are concerned with energy and states of matter. A physical change does not

produce a new substance. Changes in state or phase (melting, freezing, vaporization,

condensation, sublimation) are physical changes. Examples of physical changes include crushing

a can, melting an ice cube, and breaking a bottle.

How to Tell Chemical & Physical Changes Apart

A chemical change makes a substance that wasn't there before. There may be clues that a

chemical reaction took place, such as light, heat, color change, gas production, odor, or sound.

The starting and ending materials of a physical change are the same, even though they may look

different.

More Examples of Chemical and Physical Changes

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projects. Sign up for our free newsletter today!

More about Phases & States of Matter

• Chemical & Physical Changes Quiz

• Phase Changes Quiz

• Fire State of Matter

Chemical and Physical Properties

• Chemical Properties

• Physical Properties

• Difference Between Chemical and Physical Properties

Lean about Chemical Reactions

• Factors that Affect Reaction Rate

• Chemical Reactions in Water

• Endothermic Reaction Examples

Related Articles

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• Bubble, Bubble, Toil and Trouble - Magical Science Experiments for Kids

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Introduction

Astronomy Tools

Concepts

1. Electromagnetic Spectrum

2. Atmosphere Limitations

3. Space Observations

Equipment

1. Telescopes

2. Radio

3. Space Tools

4. Photography

5. Spectroscopy

6. Computers

7. Advanced Methods

8. Radio Astronomy

Basic Mathematics

Algebra

Statistics

Geometry

Scientific Notation

Log Scales

Calculus

Physics

Concepts

- Basic Units of Measure

- Mass & Density

- Temperature

- Velocity & Acceleration

- Force, Pressure & Energy

- Atoms

- Quantum Physics

- Nature of Light

Formulas

- Brightness

- Cepheid Rulers

- Distance

- Doppler Shift

- Frequency & Wavelength

- Hubble's Law

- Inverse Square Law

- Kinetic Energy

- Luminosity

- Magnitudes

- Convert Mass to Energy

- Kepler & Newton - Orbits

- Parallax

- Planck's Law

- Relativistic Redshift

- Relativity

Physics - Concepts - Mass and Density

In addition to the dimensions of an object - length, width, height,

radius and so on - measurements of how much stuff an object is

made and how much space the stuff fills are also measured.

Stuff can be anything: hydrogen gas, solid iron, water molecules. An

object that contains a certain amount of stuff is said to have mass,

and mass is measured by grams, kilograms, and so forth. Do not

confuse weight with mass. Generally, weight is measured by pounds,

ounces, and so on.

Mass = measure of the amount of matter within an object

Weight = measure of an object along with the effect of gravity.

The chart below demonstrates the difference between mass an weight

as compared to location. Let's say I weight 70 kg (I wish):

Earth 70 kg 154 pounds

Moon 70 kg 26 pounds

Jupiter 70 kg 391 pounds

A White Dwarf 70 kg 25,000 pounds

The amount of "stuff" in my body remains the same, thus 70 kg but

gravity affects how much I weigh. A White Dwarf is a very massive

stellar remnant, thus my weight will be incredibly high.

On Earth, there is 2.2 pounds per kilograms. For pounds to kilograms,

divide by 2.2.

Density and mass provide physical dimensions of a given object, but

are completely different in application. While mass measures the total

amount of stuff, density is how much individual particles of stuff are

within a small space within the object. It is common for density

measurement to be based on a centimeter cubed (cm3).

Density represents the mass (or number of particles) per unit volume

of a substance, material, or object.

The chart below demonstrates two types of density: mass and

particle. Mass density is the mass of an object per cm3 and particle

density is how many particles there are in the same space.

MatterMass Density (g/cm3

)

Particle Density (parts per

cm3 )

Water 1 3.7 x 1022

Lead 11.3 3.3x1022

Gold 19.3 5.9x1022

Concepts - Mass and Density http://astronomyonline.org/Science/MassDensity.asp

1 of 2 9/18/2012 6:58 PM

- Schwarzschild Radius

- Synodic & Sidereal Periods

- Sidereal Time

- Small Angle Formula

- Stellar Properties

- Stephan-Boltzmann Law

- Telescope Related

- Temperature

- Tidal Forces

- Wien's Law

Constants

Computer Models

Additional Resources

1. Advanced Topics

2. Guest Contributions

Interstellar

Space2x10-24 1

The three states of matter (solid, liquid and gas) also affect density.

If density and the space filled is known, it is possible to determine

mass by the formula:

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Concepts - Mass and Density http://astronomyonline.org/Science/MassDensity.asp

2 of 2 9/18/2012 6:58 PM

Elements, Compounds & Mixtures

Elements

Microscopic view of the atoms of

the element argon (gas phase).

Microscopic view of the molecules of

the element nitrogen (gas phase).

Note that an element:

consists of only one kind of atom,

cannot be broken down into a simpler type of matter by either physical or chemical means, and

can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).

A molecule consists of two or more atoms of the same element, or different elements, that are chemically

bound together. Note that the two nitrogen atoms which comprise a nitrogen molecule move as a unit.

Compounds

Microscopic view of the molecules of the

compound water (gas phase). Oxygen atoms are red

and hydrogen atoms are white.

Note that a compound:

consists of atoms of two or more different elements bound together,

can be broken down into a simpler type of matter (elements) by chemical means (but not by physical

means),

has properties that are different from its component elements, and

always contains the same ratio of its component atoms.

Mixtures

Elements, Compounds & Mixtures http://www.chem.purdue.edu/gchelp/atoms/elements.html

1 of 2 9/18/2012 7:06 PM

Microscopic view of a gaseous mixture containing

two elements (argon and nitrogen) and a compound

(water).

Note that a mixture:

consists of two or more different elements and/or compounds physically intermingled,

can be separated into its components by physical means, and

often retains many of the properties of its components.

Elements, Compounds & Mixtures http://www.chem.purdue.edu/gchelp/atoms/elements.html

2 of 2 9/18/2012 7:06 PM

Gases, Liquids, and Solids

Gases, liquids and solids are all made up of atoms, molecules, and/or ions, but the behaviors of these particles

differ in the three phases. The following figure illustrates the microscopic differences.

Microscopic view of a gas. Microscopic view of a liquid. Microscopic view of a solid.

Note that:

Particles in a:

gas are well separated with no regular arrangement.

liquid are close together with no regular arrangement.

solid are tightly packed, usually in a regular pattern.

Particles in a:

gas vibrate and move freely at high speeds.

liquid vibrate, move about, and slide past each other.

solid vibrate (jiggle) but generally do not move from place to place.

Liquids and solids are often referred to as condensed phases because the particles are very close together.

The following table summarizes properties of gases, liquids, and solids and identifies the microscopic behavior

responsible for each property.

Some Characteristics of Gases, Liquids and Solids and the Microscopic Explanation for

the Behavior

gas liquid solid

assumes the shape and

volume of its container

particles can move past one

another

assumes the shape of the part

of the container which it

occupies

particles can move/slide past

one another

retains a fixed volume and

shape

rigid - particles locked into

place

compressible

lots of free space between

particles

not easily compressible

little free space between

particles

not easily compressible

little free space between

particles

Gases, Liquids, and Solids http://www.chem.purdue.edu/gchelp/liquids/character.html

1 of 2 9/18/2012 7:01 PM

flows easily

particles can move past one

another

flows easily

particles can move/slide past

one another

does not flow easily

rigid - particles cannot

move/slide past one another

Gases, Liquids, and Solids http://www.chem.purdue.edu/gchelp/liquids/character.html

2 of 2 9/18/2012 7:01 PM

Chapter 3b: Force, Motion, Energy

Heat energy can be transferred by either conduction, convection or radiation.

Read: Heat Transfer, read section "Heat Energy"

When two or more objects interact, the resulting push or pull is known as force. There are two types of force: contact forces and at-a-distance forces. You should be able to identify each and give examples. Read: Types of Forces - Contact & At-A-Distance When light strikes and object reflection or refraction can occur (or both). When light rays within and object it is called absorption. When light is scattered either by reflection and/or refraction it is called diffusion. This is often done to soften the light for practical purposes. Note what happens when light is refracted through a concave lens or a convex lens. This is how eyeglasses bend light to make vision more clear. Read: Light - Refraction, Reflection Electrical energy moves with the flow of electrons. Atoms for some elements can gain or lose electrons this determines whether it has a positive charge or negative charge. Unbalanced electrical changes will seek balance which you may have experienced on a cold day with static electricity. The conductivity or resistance is determined by easily the electrons flow. When electrons flow in a circular pattern it is called a circuit. Read: Energy - Read (brief) Chapters 2, 3 & 4. Energy can be classified into two categories: potential energy and kinetic energy. Note that each has subcategories which correspond to the conceptual definition. Read: Types of Energy

http://www.energyquest.ca.gov/story/chapter01.html

http://www.physicsclassroom.com/class/newtlaws/u2l2a.cfm

http://www.myschoolhouse.com/courses/O/1/36.asp

http://www.energyquest.ca.gov/story/chapter02.html

https://angel.spcollege.edu/section/content/default.asp?WCI=pgAuthenticate&WCU=CRSCNT&ENTRY_ID=bd7083ad1104a1dd01b6976b93590DF0

https://angel.spcollege.edu/section/content/default.asp?WCI=pgAuthenticate&WCU=CRSCNT&ENTRY_ID=bd7083ad1104a1dd01b6976b93590DF0

http://www.eia.gov/kids/energy.cfm?page=about_forms_of_energy-basics

Sir Isaac Newton devised three laws of motion which are still used in physics. You should know the laws and how they translate into the real world. Which one explains why the more you fill up a grocery cart, the more force you need to push it to make it move? Which one explains how a fish swims upstream? Which one is also known as the law of inertia? Read Newton's Three Laws

http://www.physicsclassroom.com/Class/newtlaws/

Heat Energy

Heat is a form of energy. We use it for a lot of things, like warming our homes and cooking our

food.

Heat energy moves in three ways:

1. Conduction

2. Convection

3. Radiation

Conduction occurs when energy is passed directly from one item to another. If you stirred a pan

of soup on the stove with a metal spoon, the spoon will heat up. The heat is being conducted

from the hot area of the soup to the colder area of spoon.

Metals are excellent conductors of heat energy.

Wood or plastics are not. These "bad" conductors

are called insulators. That's why a pan is usually

made of metal while the handle is made of a

strong plastic.

Convection is the movement of gases or liquids

from a cooler spot to a warmer spot. If a soup pan

is made of glass, we could see the movement of

convection currents in the pan. The warmer soup

moves up from the heated area at the bottom of

the pan to the top where it is cooler. The cooler

soup then moves to take the warmer soup's place.

The movement is in a circular pattern within the

pan (see picture above).

The wind we feel outside is often the result of

convection currents. You can understand this by

the winds you feel near an ocean. Warm air is

lighter than cold air and so it rises. During the

daytime, cool air over water moves to replace the

air rising up as the land warms the air over it.

During the nighttime, the directions change - the

surface of the water is sometimes warmer and the

land is cooler.

Radiation is the final form of movement of heat

energy. The sun's light and heat cannot reach us

by conduction or convection because space is

almost completely empty. There is nothing to transfer the

energy from the sun to the earth.

The sun's rays travel in straight lines called heat rays.

When it moves that way, it is called radiation.

When sunlight hits the earth, its radiation is absorbed or

reflected. Darker surfaces absorb more of the radiation

and lighter surfaces reflect the radiation. So you would be

cooler if you wear light or white clothes in the summer.

Student Extras

Teacher's Guide

Force and Its Representation

The Meaning of Force | Types of Forces | Drawing Free-Body Diagrams

Determining the Net Force

The Meaning of Force

A force is a push or pull upon an object resulting from the object's interaction with another

object. Whenever there is an interaction between two objects, there is a force upon each of the

objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an

interaction.

For simplicity sake, all forces (interactions) between objects can be placed into two broad categories:

contact forces, and

forces resulting from action-at-a-distance

Contact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting

each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied

forces. These specific forces will be discussed in more detail later in Lesson 2 as well as in other lessons.

Action-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical

contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance

forces include gravitational forces. For example, the sun and planets exert a gravitational pull on each other despite their large

spatial separation. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a

gravitational pull between you and the Earth. Electric forces are action-at-a-distance forces. For example, the protons in the

nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small

spatial separation. And magnetic forces are action-at-a-distance forces. For example, two magnets can exert a magnetic pull on

each other even when separated by a distance of a few centimeters. These specific forces will be discussed in more detail later in

Lesson 2 as well as in other lessons.

Examples of contact and action-at-distance forces are listed in the table below.

Contact Forces Action-at-a-Distance ForcesFrictional Force Gravitational Force

Tension Force Electrical Force

Normal Force Magnetic Force

Air Resistance Force

Applied Force

Spring Force

Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an "N."

To say "10.0 N" means 10.0 Newton of force. One Newton is the amount of force required to give a 1-kg mass an acceleration of

1 m/s/s. Thus, the following unit equivalency can be stated:

A force is a vector quantity. As learned in an earlier unit, a vector quantity is a quantity that has both magnitude and direction.

To fully describe the force acting upon an object, you must describe both the magnitude (size or numerical value) and the

direction. Thus, 10 Newton is not a full description of the force acting upon an object. In contrast, 10 Newton, downward is a

complete description of the force acting upon an object; both the magnitude (10 Newton) and the direction (downward) are

given.

Because a force is a vector that has a direction, it is common to represent forces using diagrams in

which a force is represented by an arrow. Such vector diagrams were introduced in an earlier unit

and are used throughout the study of physics. The size of the arrow is reflective of the magnitude of

the force and the direction of the arrow reveals the direction that the force is acting. (Such diagrams

are known as free-body diagrams and are discussed later in this lesson.) Furthermore, because

forces are vectors, the effect of an individual force upon an object is often canceled by the effect of

another force. For example, the effect of a 20-Newton upward force acting upon a book is canceled

by the effect of a 20-Newton downward force acting upon the book. In such instances, it is said that

the two individual forces balance each other; there would be no unbalanced force acting upon the

book.

Other situations could be imagined in which two of the individual vector forces cancel each other

("balance"), yet a third individual force exists that is not balanced by another force. For

example, imagine a book sliding across the rough surface of a table from left to right. The

downward force of gravity and the upward force of the table supporting the book act in opposite

directions and thus balance each other. However, the force of friction acts leftwards, and there is

no rightward force to balance it. In this case, an unbalanced force acts upon the book to change

its state of motion.

The exact details of drawing free-body diagrams are discussed later. For now, the emphasis is upon the fact that a force is a

vector quantity that has a direction. The importance of this fact will become clear as we analyze the individual forces acting upon

an object later in this lesson.

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Reflection & Refraction

Reflection occurs when light bounces off objects. Howmuch reflection depends upon how even the surface is. If the surface is rough, the light scatters. If the surface issmooth and flat, the light will bounce off it at equalangles. That is why a flat mirror reflects a good likenessof the object being reflected.

Look at the diagrams below. Notice the angles at whichthe rays of light strike the surfaces.

Refraction occurs because light bends. A lens is apiece of transparent material. It is usually made of glassand has at least one curved surface. Look at the convexand concave lenses below.

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The curved surface/surfaces of a lens bends the light. Notice the paths of light of the convex and concavelenses shown below.

Directions: Answer the questions about reflection and

refraction.

Reflection occurs when light bounces off an object.

Refraction occurs when light is bent.

When light strikes a surface that is rough, the light will scatter .

When light strikes a surface that is smooth, the light willbounce off at equal angles .

What type of material is a lens?

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transparent

translucent

opaque

The path of light through a concave lens is

not directed to a single focal point

directed to a single focal point

The path of light through a convex lens is

not directed to a single focal point

directed to a single focal point

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Chapter 2: What Is Electricity?

Electricity figures everywhere in our lives. Electricity lights up our

homes, cooks our food, powers our computers, television sets, and other

electronic devices. Electricity from batteries keeps our cars running and

makes our flashlights shine in the dark.

Here's something you can do to see the importance of electricity. Take a

walk through your school, house or apartment and write down all the

different appliances, devices and machines that use electricity. You'll be

amazed at how many things we use each and every day that depend on

electricity.

But what is electricity? Where does it come from? How does it work?

Before we understand all that, we need to know a little bit about atoms

and their structure.

All matter is made up of atoms, and atoms are made up

of smaller particles. The three main particles making

up an atom are the proton, the neutron and the electron.

Electrons spin around the center, or nucleus, of atoms,

in the same way the moon spins around the earth. The

nucleus is made up of neutrons and protons.

Electrons contain a negative charge, protons a positive

charge. Neutrons are neutral – they have neither a positive nor a negative

charge.

There are many different kinds of atoms, one for each type of element.

An atom is a single part that makes up an element. There are 118

different known elements that make up every thing! Some elements like

oxygen we breathe are essential to life.

Each atom has a specific number of electrons,

protons and neutrons. But no matter how many

particles an atom has, the number of electrons

usually needs to be the same as the number of protons. If the numbers

are the same, the atom is called balanced, and it is very stable.

So, if an atom had six protons, it should also have six electrons. The

element with six protons and six electrons is called carbon. Carbon is

found in abundance in the sun, stars, comets, atmospheres of most

planets, and the food we eat. Coal is made of carbon; so are diamonds.

Some kinds of atoms have loosely attached electrons. An atom that loses

electrons has more protons than electrons and is positively charged. An

atom that gains electrons has more negative particles and is negatively

charge. A "charged" atom is called an "ion."

Electrons can be made to move from one atom to another. When those

electrons move between the atoms, a current of electricity is created. The

electrons move from one atom to another in a "flow." One electron is

attached and another electron is lost.

This chain is similar to the fire fighter's bucket brigades in olden times.

But instead of passing one bucket from the start of the line of people to

the other end, each person would have a bucket of water to pour from

one bucket to another. The result was a lot of spilled water and not

enough water to douse the fire. It is a situation that's very similar to

electricity passing along a wire and a circuit. The charge is passed from

atom to atom when electricity is "passed."

Scientists and engineers have learned many ways to move electrons off

of atoms. That means that when you add up the electrons and protons,

you would wind up with one more proton instead of being balanced.

Since all atoms want to be balanced, the atom that has been

"unbalanced" will look for a free electron to fill the place of the missing

one. We say that this unbalanced atom has a "positive charge" (+)

because it has too many protons.

Since it got kicked off, the free electron moves around waiting for an

unbalanced atom to give it a home. The free electron charge is negative,

and has no proton to balance it out, so we say that it has a "negative

charge" (-).

So what do positive and negative charges have to do with electricity?

Scientists and engineers have found several ways to create large

numbers of positive atoms and free negative electrons. Since positive

atoms want negative electrons so they can be balanced, they have a

strong attraction for the electrons. The electrons also want to be part of a

balanced atom, so they have a strong attraction to the positive atoms. So,

the positive attracts the negative to balance out.

The more positive atoms or negative electrons you have, the stronger the

attraction for the other. Since we have both positive and negative

charged groups attracted to each other, we call the total attraction

"charge."

Energy also can be measured in joules. Joules sounds exactly like the

word jewels, as in diamonds and emeralds. A thousand joules is equal to

a British thermal unit.

When electrons move among the atoms of matter, a current of electricity

is created. This is what happens in a piece of wire. The electrons are

passed from atom to atom, creating an electrical current from one end to

other, just like in the picture.

Electricity is conducted through some things better than others do. Its

resistance measures how well something conducts electricity. Some

things hold their electrons very tightly. Electrons do not move through

them very well. These things are called insulators. Rubber, plastic, cloth,

glass and dry air are good insulators and have very high resistance.

Other materials have some loosely held electrons, which move through

them very easily. These are called conductors. Most metals – like

copper, aluminum or steel – are good conductors.

Chapter 3: Resistance and Static Electricity

As we have learned, some kinds of atoms contain

loosely attached electrons. Electrons can be made

to move easily from one atom to another. When

those electrons move among the atoms of matter,

a current of electricity is created.

Take a piece of wire. The electrons are passed

from atom to atom, creating an electrical current from one end to the

other. Electrons are very, very small. A single copper penny contains

more than 10,000,000,000,000,000,000,000 (1x1022) electrons.

Electricity "flows" or moves through some things better than others do.

The measurement of how well something conducts electricity is called

its resistance.

Resistance in wire depends on how thick and how long it is, and what

it's made of. The thickness of wire is called its gauge. The smaller the

gauge, the bigger the wire. Some of the largest thicknesses of regular

wire is gauge 1.

Different types of metal are used in making wire. You can have copper

wire, aluminum wire, even steel wire. Each of these metals has a

different resistance; how well the metal conducts electricity. The lower

the resistance of a wire, the better it conducts electricity.

Copper is used in many wires because it has a lower resistance than

many other metals. The wires in your walls, inside your lamps and

elsewhere are usually copper.

A piece of metal can be made to act like a heater. When an electrical

current occurs, the resistance causes friction and the friction causes heat.

The higher the resistance, the hotter it can get. So, a coiled wire high in

resistance, like the wire in a hair dryer, can be very hot.

Some things conduct electricity very poorly. These are called insulators.

Rubber is a good insulator, and that's why rubber is used to cover wires

in an electric cord. Glass is another good insulator. If you look at the end

of a power line, you'll see that it is attached to some bumpy looking

things. These are glass insulators. They keep the metal of the wires from

touching the metal of the towers.

Chapter 4: Circuits

Electrons with a negative charge, can't "jump" through the air to a

positively charged atom. They have to wait until there is a link or bridge

between the negative area and the positive area. We usually call this

bridge a "circuit."

When a bridge is created, the electrons begin moving quickly.

Depending on the resistance of the material making up the bridge, they

try to get across as fast as they can. If you're not careful, too many

electrons can go across at one time and destroy the "bridge" or the

circuit, in the process.

In Chapter 3, we learned about electrons and the attraction between

positive and negative charges. We also learned that we can create a

bridge called a "circuit" between the charges.

We can limit the number of electrons crossing over the "circuit," by

letting only a certain number through at a time. And we can make

electricity do something for us while they are on their way. For example,

we can "make" the electrons "heat" a filament in a bulb, causing it to

glow and give off light.

When we limit the number of electrons that can cross over our circuit,

we say we are giving it "resistance". We "resist" letting all the electrons

through. This works something like a tollbooth on a freeway bridge.

Copper wire is just one type of bridge we use in circuits

.

Before electrons can move far, however, they can collide with one of the

atoms along the way. This slows them down or even reverses their

direction. As a result, they lose energy to the atoms. This energy appears

as heat, and the scattering is a resistance to the current.

Think of the bridge as a garden hose. The current of electricity is the

water flowing in the hose and the water pressure is the voltage of a

circuit. The diameter of the hose is the determining factor for the

resistance.

Current refers to the movement of charges. In an electrical circuit –

electrons move from the negative pole to the positive. If you connected

the positive pole of an electrical source to the negative pole, you create a

circuit. This charge changes into electrical energy when the poles are

connected in a circuit – similar to connecting the two poles on opposite

ends of a battery.

Along the circuit you can have a light bulb and an on-off switch. The

light bulb changes the electrical energy into light and heat energy.

Electricity figures everywhere in our lives. Electricity lights up our homes, cooks our

food, powers our computers, television sets, and other electronic devices. Electricity

from batteries keeps our cars running and makes our flashlights shine in the dark.

Here's something you can do to see the importance of electricity. Take a walk through

your school, house or apartment and write down all the different appliances, devices

and machines that use electricity. You'll be amazed at how many things we use each

and every day that depend on electricity.

But what is electricity? Where does it come from? How does it work? Before we

understand all that, we need to know a little bit about atoms and their structure.

All matter is made up of atoms, and atoms are made

up of smaller particles. The three main particles making

up an atom are the proton, the neutron and the

electron.





charge. Neutrons are neutral – they have neither a

positive nor a negative charge.

There are many different kinds of atoms, one for each

type of element. An atom is a single part that makes up

an element. There are 118 different known elements that make up every thing! Some

elements like oxygen we breathe are essential to life.




usually needs to be the same as the number of

protons. If the numbers are the same, the atom is

called balanced, and it is very stable.

So, if an atom had six protons, it should also have

six electrons. The element with six protons and six

electrons is called carbon. Carbon is found in

abundance in the sun, stars, comets, atmospheres

of most planets, and the food we eat. Coal is made

of carbon; so are diamonds.

Some kinds of atoms have loosely attached

electrons. An atom that loses electrons has more protons than electrons and is

positively charged. An atom that gains electrons has more negative particles and is

negatively charge. A "charged" atom is called an "ion."

Electrons can be made to move from one atom to another. When those electrons

move between the atoms, a current of electricity is created. The electrons move from

one atom to another in a "flow." One electron is attached and another electron is lost.

This chain is similar to the fire fighter's bucket brigades in olden times. But instead of

passing one bucket from the start of the line of people to the other end, each person

would have a bucket of water to pour from one bucket to another. The result was a

lot of spilled water and not enough water to douse the fire. It is a situation that's very

similar to electricity passing along a wire and a circuit. The charge is passed from


Scientists and engineers have learned many ways to move electrons off of atoms.

That means that when you add up the electrons and protons, you would wind up

with one more proton instead of being balanced.

Since all atoms want to be balanced, the atom that has been "unbalanced" will look

for a free electron to fill the place of the missing one. We say that this unbalanced

atom has a "positive charge" (+) because it has too many protons.

Since it got kicked off, the free electron moves around waiting for an unbalanced

atom to give it a home. The free electron charge is negative, and has no proton to

balance it out, so we say that it has a "negative charge" (-).


Scientists and engineers have found several ways to create large numbers of positive

atoms and free negative electrons. Since positive atoms want negative electrons so

they can be balanced, they have a strong attraction for the electrons. The electrons

also want to be part of a balanced atom, so they have a strong attraction to the

positive atoms. So, the positive attracts the negative to balance out.

The more positive atoms or negative electrons you have, the stronger the attraction

for the other. Since we have both positive and negative charged groups attracted to

each other, we call the total attraction "charge."

Energy also can be measured in joules. Joules sounds exactly like the word jewels, as

in diamonds and emeralds. A thousand joules is equal to a British thermal unit.

When electrons move among the atoms of matter, a current of electricity is created.

This is what happens in a piece of wire. The electrons are passed from atom to atom,

creating an electrical current from one end to other, just like in the picture.

Electricity is conducted through some things better than others do. Its resistance

measures how well something conducts electricity. Some things hold their electrons

very tightly. Electrons do not move through them very well. These things are called

insulators. Rubber, plastic, cloth, glass and dry air are good insulators and have very

high resistance.

Other materials have some loosely held electrons, which move through them very

easily. These are called conductors. Most metals – like copper, aluminum or steel –

are good conductors.


The Energy Story - Chapter 2: What Is Electricity? http://www.energyquest.ca.gov/story/chapter02.html

1 of 1 9/21/2012 9:05 AM

What Is Energy?

Forms of Energy

Forms of Energy Basics

What Is Energy?

Energy makes change possible. We use it to do things for us. It moves cars along the

road and boats over the water. It bakes a cake in the oven and keeps ice frozen in the

freezer. It plays our favorite songs on the radio and lights our homes. Energy is needed

for our bodies to grow and it allows our minds to think.

Scientists define energy as the ability to do work. Modern civilization is possible

because we have learned how to change energy from one form to another and use it to

do work for us and to live more comfortably.

Forms of Energy

Energy is found in different forms including light, heat, chemical, and motion. There are

many forms of energy, but they can all be put into two categories: potential and kinetic.

Potential Energy

Potential energy is stored energy and the energy of position

— gravitational energy. There are several forms of potential

energy.

Kinetic Energy

Kinetic energy is motion — of waves, electrons, atoms,

molecules, substances, and objects.

Chemical Energy is energy stored in the bonds of atoms

and molecules. Batteries, biomass, petroleum, natural gas,

and coal are examples of stored chemical energy. Chemical

energy is converted to thermal energy when we burn wood in

a fireplace or burn gasoline in a car's engine.

Mechanical Energy is energy stored in objects by tension.

Compressed springs and stretched rubber bands are

examples of stored mechanical energy.

Nuclear Energy is energy stored in the nucleus of an atom

— the energy that holds the nucleus together. Very large

Radiant Energy is electromagnetic energy that travels in

transverse waves. Radiant energy includes visible light, x-rays,

gamma rays and radio waves. Light is one type of radiant

energy. Sunshine is radiant energy, which provides the fuel

and warmth that make life on Earth possible.

Thermal Energy, or heat, is the vibration and movement of

the atoms and molecules within substances. As an object is

heated up, its atoms and molecules move and collide faster.

Geothermal energy is the thermal energy in the Earth.

Motion Energy is energy stored in the movement of objects.

EIA Energy Kids - Forms of Energy http://www.eia.gov/kids/energy.cfm?page=about_forms_of_energy-basics

1 of 2 9/18/2012 7:17 PM

amounts of energy can be released when the nuclei are

combined or split apart. Nuclear power plants split the nuclei

of uranium atoms in a process called fission. The sun

combines the nuclei of hydrogen atoms in a process called

fusion.

Gravitational Energy is energy stored in an object's height.

The higher and heavier the object, the more gravitational

energy is stored. When you ride a bicycle down a steep hill

and pick up speed, the gravitational energy is being converted

to motion energy. Hydropower is another example of

gravitational energy, where the dam "piles" up water from a

river into a reservoir.

The faster they move, the more energy is stored. It takes

energy to get an object moving, and energy is released when

an object slows down. Wind is an example of motion energy.

A dramatic example of motion is a car crash, when the car

comes to a total stop and releases all its motion energy at

once in an uncontrolled instant.

Sound is the movement of energy through substances in

longitudinal (compression/rarefaction) waves. Sound is

produced when a force causes an object or substance to

vibrate — the energy is transferred through the substance in a

wave. Typically, the energy in sound is far less than other

forms of energy.

Electrical Energy is delivered by tiny charged particles

called electrons, typically moving through a wire. Lightning is

an example of electrical energy in nature, so powerful that it is

not confined to a wire.

EIA Energy Kids - Forms of Energy http://www.eia.gov/kids/energy.cfm?page=about_forms_of_energy-basics

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Newton's Laws

Vectors - Motion and

Forces in Two Dimensions

Momentum and Its

Conservation

Work, Energy, and Power

Circular Motion and

Satellite Motion

Thermal Physics

Static Electricity

Current Electricity

Waves

Sound Waves and Music

Light Waves and Color

Reflection and Ray Model

of Light

Refraction and Ray Model

of Light

Minds on Physics

The Calculator Pad

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The Review Session

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» The Physics Classroom » Physics Tutorial » Newton's Laws

Newton's Laws - Lesson 1

Newton's First Law of Motion

Newton's First Law | Inertia and Mass | State of Motion | Balanced and Unbalanced Forces

Newton's First Law

In a previous chapter of study, the variety of ways by which motion can be described (words,

graphs, diagrams, numbers, etc.) was discussed. In this unit (Newton's Laws of Motion), the

ways in which motion can be explained will be discussed. Isaac Newton (a 17th century scientist) put forth a variety of laws that

explain why objects move (or don't move) as they do. These three laws have become known as Newton's three laws of motion.

The focus of Lesson 1 is Newton's first law of motion - sometimes referred to as the law of inertia.

Newton's first law of motion is often stated as

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same

direction unless acted upon by an unbalanced force.

There are two parts to this statement - one that predicts the behavior of stationary objects and the other that predicts the

behavior of moving objects. The two parts are summarized in the following diagram.

The behavior of all objects can be described by saying that objects tend to "keep on

doing what they're doing" (unless acted upon by an unbalanced force). If at rest, they

will continue in this same state of rest. If in motion with an eastward velocity of 5 m/s,

they will continue in this same state of motion (5 m/s, East). If in motion with a

leftward velocity of 2 m/s, they will continue in this same state of motion (2 m/s, left).

The state of motion of an object is maintained as long as the object is not acted upon by

an unbalanced force. All objects resist changes in their state of motion - they tend to

"keep on doing what they're doing."

Suppose that you filled a baking dish to the rim with water and walked around an oval track making an attempt to complete a

lap in the least amount of time. The water would have a tendency to spill from the container during specific locations on the

track. In general the water spilled when:

the container was at rest and you attempted to move it

the container was in motion and you attempted to stop it

the container was moving in one direction and you attempted to change its direction.

The water spills whenever the state of motion of the container is changed. The water

resisted this change in its own state of motion. The water tended to "keep on doing what

it was doing." The container was moved from rest to a high speed at the starting line;

the water remained at rest and spilled onto the table. The container was stopped near

the finish line; the water kept moving and spilled over container's leading edge. The

container was forced to move in a different direction to make it around a curve; the water

kept moving in the same direction and spilled over its edge. The behavior of the water

during the lap around the track can be explained by Newton's first law of motion.

Everyday Applications of Newton's First Law

There are many applications of Newton's first law of motion. Consider some of your experiences in an automobile. Have you ever

observed the behavior of coffee in a coffee cup filled to the rim while starting a car from rest or while bringing a car to rest from a

state of motion? Coffee "keeps on doing what it is doing." When you accelerate a car from rest, the road provides an unbalanced

force on the spinning wheels to push the car forward; yet the coffee (that was at rest) wants to stay at rest. While the car

accelerates forward, the coffee remains in the same position; subsequently, the car accelerates out from under the coffee and the

coffee spills in your lap. On the other hand, when braking from a state of motion the coffee continues forward with the same

speed and in the same direction, ultimately hitting the windshield or the dash. Coffee in motion stays in motion.

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Have you ever experienced inertia (resisting changes in your state of motion) in an

automobile while it is braking to a stop? The force of the road on the locked wheels

provides the unbalanced force to change the car's state of motion, yet there is no

unbalanced force to change your own state of motion. Thus, you continue in motion,

sliding along the seat in forward motion. A person in motion stays in motion with the

same speed and in the same direction ... unless acted upon by the unbalanced force

of a seat belt. Yes! Seat belts are used to provide safety for passengers whose

motion is governed by Newton's laws. The seat belt provides the unbalanced force

that brings you from a state of motion to a state of rest. Perhaps you could speculate

what would occur when no seat belt is used.

There are many more applications of Newton's first law of motion. Several applications are listed below.

Perhaps you could think about the law of inertia and provide explanations for each application.

Blood rushes from your head to your feet while quickly stopping when riding on a descending

elevator.

The head of a hammer can be tightened onto the wooden handle by banging the bottom of the

handle against a hard surface.

A brick is painlessly broken over the hand of a physics teacher by slamming it with a hammer.

(CAUTION: do not attempt this at home!)

To dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and thrusted

downward at high speeds and then abruptly halted.

Headrests are placed in cars to prevent whiplash injuries during rear-end collisions.

While riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or

rock or other object that abruptly halts the motion of the skateboard.

Try This At Home

Acquire a metal coat hanger for which you have permission to destroy. Pull

the coat hanger apart. Using duct tape, attach two tennis balls to opposite

ends of the coat hanger as shown in the diagram at the right. Bend the

hanger so that there is a flat part that balances on the head of a person.

The ends of the hanger with the tennis balls should hang low (below the

balancing point). Place the hanger on your head and balance it. Then

quickly spin in a circle. What do the tennis balls do?

Next Section: Inertia and Mass

Jump To Lesson 2: Force and Its Representation

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Newton's Laws of Motion


Inertia and Mass

Newton's first law of motion states that "An object at

rest stays at rest and an object in motion stays in

motion with the same speed and in the same direction

unless acted upon by an unbalanced force." Objects

tend to "keep on doing what they're doing." In fact, it

is the natural tendency of objects to resist changes in

their state of motion. This tendency to resist changes in

their state of motion is described as inertia.

Inertia: the resistance an object has to a change in its state of motion.

Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. The dominant thought prior

to Newton's day was that it was the natural tendency of objects to come to a rest position. Moving objects, so it was believed,

would eventually stop moving; a force was necessary to keep an object moving. But if left to itself, a moving object would

eventually come to rest and an object at rest would stay at rest; thus, the idea that dominated people's thinking for nearly 2000

years prior to Newton was that it was the natural tendency of all objects to assume a rest position.

Galileo and the Concept of Inertia

Galileo, a premier scientist in the seventeenth century, developed the concept of inertia. Galileo reasoned that moving objects

eventually stop because of a force called friction. In experiments using a pair of inclined planes facing each other, Galileo

observed that a ball would roll down one plane and up the opposite plane to approximately the same height. If smoother planes

were used, the ball would roll up the opposite plane even closer to the original height. Galileo reasoned that any difference

between initial and final heights was due to the presence of friction. Galileo postulated that if friction could be entirely

eliminated, then the ball would reach exactly the same height.

Galileo further observed that regardless of the angle at which the planes were oriented, the final height was almost always equal

to the initial height. If the slope of the opposite incline were reduced, then the ball would roll a further distance in order to reach

that original height.

Galileo's reasoning continued - if the opposite incline were elevated at nearly a 0-degree angle, then the ball would roll almost

forever in an effort to reach the original height. And if the opposing incline was not even inclined at all (that is, if it were oriented

along the horizontal), then ... an object in motion would continue in motion... .

Forces Don't Keep Objects Moving

Isaac Newton built on Galileo's thoughts about motion. Newton's first law of motion


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declares that a force is not needed to keep an object in motion. Slide a book across a

table and watch it slide to a rest position. The book in motion on the table top does not

come to a rest position because of the absence of a force; rather it is the presence of a

force - that force being the force of friction - that brings the book to a rest position. In

the absence of a force of friction, the book would continue in motion with the same

speed and direction - forever! (Or at least to the end of the table top.) A force is not

required to keep a moving book in motion. In actuality, it is a force that brings the book to rest.

Mass as a Measure of the Amount of Inertia

All objects resist changes in their state of motion. All objects have this tendency - they

have inertia. But do some objects have more of a tendency to resist changes than others?

Absolutely yes! The tendency of an object to resist changes in its state of motion varies

with mass. Mass is that quantity that is solely dependent upon the inertia of an object. The

more inertia that an object has, the more mass that it has. A more massive object has a

greater tendency to resist changes in its state of motion.

Suppose that there are two seemingly identical bricks at rest on the physics lecture table.

Yet one brick consists of mortar and the other brick consists of Styrofoam. Without lifting

the bricks, how could you tell which brick was the Styrofoam brick? You could give the

bricks an identical push in an effort to change their state of motion. The brick that offers

the least resistance is the brick with the least inertia - and therefore the brick with the least mass (i.e., the Styrofoam brick).

A common physics demonstration relies on this principle that the more massive the object, the more

that object resist changes in its state of motion. The demonstration goes as follows: several massive

books are placed upon a teacher's head. A wooden board is placed on top of the books and a hammer is

used to drive a nail into the board. Due to the large mass of the books, the force of the hammer is

sufficiently resisted (inertia). This is demonstrated by the fact that the teacher does not feel the

hammer blow. (Of course, this story may explain many of the observations that you previously have

made concerning your "weird physics teacher.") A common variation of this demonstration involves

breaking a brick over the teacher's hand using the swift blow of a hammer. The massive bricks resist

the force and the hand is not hurt. (CAUTION: do not try these demonstrations at home.)

Watch It!

A physics instructor explains the property of inertia using a phun physics demonstration.


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Check Your Understanding

1. Imagine a place in the cosmos far from all gravitational and frictional influences. Suppose that

you visit that place (just suppose) and throw a rock. The rock will

a. gradually stop.

b. continue in motion in the same direction at constant speed.

See Answer

2. A 2-kg object is moving horizontally with a speed of 4 m/s. How much net force is required to keep the object moving at this

speed and in this direction?

See Answer

3. Mac and Tosh are arguing in the cafeteria. Mac says that if he flings the Jell-O with a greater speed it

will have a greater inertia. Tosh argues that inertia does not depend upon speed, but rather upon mass.

Who do you agree with? Explain why.

See Answer

4. Supposing you were in space in a weightless environment, would it require a force to set an object in motion?

See Answer

5. Fred spends most Sunday afternoons at rest on the sofa, watching pro football games and consuming large quantities of food.

What effect (if any) does this practice have upon his inertia? Explain.

See Answer

6. Ben Tooclose is being chased through the woods by a bull moose that he was attempting to photograph. The enormous mass

of the bull moose is extremely intimidating. Yet, if Ben makes a zigzag pattern through the woods, he will be able to use the

large mass of the moose to his own advantage. Explain this in terms of inertia and Newton's first law of motion.

See Answer

7. Two bricks are resting on edge of the lab table. Shirley Sheshort stands on her toes and spots the two bricks. She acquires an

intense desire to know which of the two bricks are most massive. Since Shirley is vertically challenged, she is unable to reach

high enough and lift the bricks; she can however reach high enough to give the bricks a push. Discuss how the process of

pushing the bricks will allow Shirley to determine which of the two bricks is most massive. What difference will Shirley observe

and how can this observation lead to the necessary conclusion?

See Answer

Next Section: State of Motion


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Newton's Laws of Motion


State of Motion

Inertia is the tendency of an object to resist changes in its state of motion. But what is meant

by the phrase state of motion? The state of motion of an object is defined by its velocity - the

speed with a direction. Thus, inertia could be redefined as follows:

Inertia: tendency of an object to resist changes in its velocity.

An object at rest has zero velocity - and (in the absence of an unbalanced force) will remain with a zero velocity. Such an object

will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. An object in motion with a velocity

of 2 m/s, East will (in the absence of an unbalanced force) remain in motion with a velocity of 2 m/s, East. Such an object will

not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. Objects resist changes in their velocity.

As learned in an earlier unit, an object that is not changing its velocity is said to have an acceleration of 0 m/s/s. Thus, we could

provide an alternative means of defining inertia:

Inertia: tendency of an object to resist accelerations.

Watch It!

An air track glider is shown moving across an air track. Air is blown through many small holes in the track in order to lift the

glider off the track. This reduces, maybe even eliminates, the action of surface friction upon the glider. The glider moves with

what seems to be a constant speed motion. As they say: objects in motion stay in motion ... .


1. A group of physics teachers is taking some time off for a little putt-putt golf. The 15th hole at the

Hole-In-One Putt-Putt Golf Course has a large metal rim that putters must use to guide their ball

towards the hole. Mr. S guides a golf ball around the metal rim When the ball leaves the rim, which

path (1, 2, or 3) will the golf ball follow?

See Answer


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2. A 4.0-kg object is moving across a friction-free surface with a constant velocity of 2 m/s. Which one of the following horizontal

forces is necessary to maintain this state of motion?

a. 0 N b. 0.5 N c. 2.0 N d. 8.0 N

e. depends on the speed.

See Answer

Next Section: Balanced and Unbalanced Forces


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Newton's First Law of Motion


Balanced and Unbalanced Forces

Newton's first law of motion has been frequently stated throughout this lesson.

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction

unless acted upon by an unbalanced force.

But what exactly is meant by the phrase unbalanced force? What is an unbalanced force? In pursuit of an answer, we will first

consider a physics book at rest on a tabletop. There are two forces acting upon the book. One force - the Earth's gravitational pull

- exerts a downward force. The other force - the push of the table on the book (sometimes referred to as a normal force) - pushes

upward on the book.

Since these two forces are of equal magnitude and in opposite directions, they balance each other. The book is said to be at

equilibrium. There is no unbalanced force acting upon the book and thus the book maintains its state of motion. When all the

forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate. (Note: diagrams such as

the one above are known as free-body diagrams and will be discussed in detail in Lesson 2.)

Consider another example involving balanced forces - a person standing upon the ground. There are two forces acting upon the

person. The force of gravity exerts a downward force. The floor of the floor exerts an upward force.

Since these two forces are of equal magnitude and in opposite directions, they balance each other. The person is at equilibrium.

There is no unbalanced force acting upon the person and thus the person maintains its state of motion. (Note: diagrams such as

the one above are known as free-body diagrams and will be discussed in detail in Lesson 2.)

Now consider a book sliding from left to right across a tabletop. Sometime in the prior history of the book, it may have been

given a shove and set in motion from a rest position. Or perhaps it acquired its motion by sliding down an incline from an

elevated position. Whatever the case, our focus is not upon the history of the book but rather upon the current situation of a book

sliding to the right across a tabletop. The book is in motion and at the moment there is no one pushing it to the right.

(Remember: a force is not needed to keep a moving object moving to the right.) The forces acting upon the book are shown

below.


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The force of gravity pulling downward and the force of the table pushing upwards on the book are of equal magnitude and

opposite directions. These two forces balance each other. Yet there is no force present to balance the force of friction. As the book

moves to the right, friction acts to the left to slow the book down. There is an unbalanced force; and as such, the book changes

its state of motion. The book is not at equilibrium and subsequently accelerates. Unbalanced forces cause accelerations. In this

case, the unbalanced force is directed opposite the book's motion and will cause it to slow down. (Note: diagrams such as the

one above are known as free-body diagrams and will be discussed in detail in Lesson 2.)

To determine if the forces acting upon an object are balanced or unbalanced, an analysis must first be conducted to determine

what forces are acting upon the object and in what direction. If two individual forces are of equal magnitude and opposite

direction, then the forces are said to be balanced. An object is said to be acted upon by an unbalanced force only when there is

an individual force that is not being balanced by a force of equal magnitude and in the opposite direction. Such analyses are

discussed in Lesson 2 of this unit and applied in Lesson 3.


Luke Autbeloe drops an approximately 5.0 kg fat cat (weight = 50.0 N) off the roof of his house into the swimming pool below.

Upon encountering the pool, the cat encounters a 50.0 N upward resistance force (assumed to be constant). Use this description

to answer the following questions. Click the button to view the correct answers.

1. Which one of the velocity-time graphs best describes the motion of the cat? Support your answer with sound reasoning.

See Answer

2. Which one of the following dot diagrams best describes the motion of the falling cat from the time that they are dropped to

the time that they hit the bottom of the pool? The arrows on the diagram represent the point at which the cat hits the water.

Support your answer with sound reasoning.

See Answer

3. Several of Luke's friends were watching the motion of the falling cat. Being "physics types", they began discussing the motion

and made the following comments. Indicate whether each of the comments is correct or incorrect? Support your answers.

a. Once the cat hits the water, the forces are balanced and the cat will stop.

See Answer

b. Upon hitting the water, the cat will accelerate upwards because the water applies an upward force.

See Answer

c. Upon hitting the water, the cat will bounce upwards due to the upward force.

See Answer

4. If the forces acting upon an object are balanced, then the object


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a. must not be moving.

b. must be moving with a constant velocity.

c. must not be accelerating.

d. none of these

See Answer


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The Meaning of Force

A force is a push or pull upon an object resulting from the object's interaction with another

object. Whenever there is an interaction between two objects, there is a force upon each of the

objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an

interaction.

For simplicity sake, all forces (interactions) between objects can be placed into two broad categories:

contact forces, and

forces resulting from action-at-a-distance

Contact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting

each other. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied

forces. These specific forces will be discussed in more detail later in Lesson 2 as well as in other lessons.

Action-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical

contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance

forces include gravitational forces. For example, the sun and planets exert a gravitational pull on each other despite their large

spatial separation. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a

gravitational pull between you and the Earth. Electric forces are action-at-a-distance forces. For example, the protons in the

nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small

spatial separation. And magnetic forces are action-at-a-distance forces. For example, two magnets can exert a magnetic pull on

each other even when separated by a distance of a few centimeters. These specific forces will be discussed in more detail later in

Lesson 2 as well as in other lessons.

Examples of contact and action-at-distance forces are listed in the table below.





Applied Force

Spring Force

Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an "N."

To say "10.0 N" means 10.0 Newton of force. One Newton is the amount of force required to give a 1-kg mass an acceleration of

1 m/s/s. Thus, the following unit equivalency can be stated:

A force is a vector quantity. As learned in an earlier unit, a vector quantity is a quantity that has both magnitude and direction.

To fully describe the force acting upon an object, you must describe both the magnitude (size or numerical value) and the

direction. Thus, 10 Newton is not a full description of the force acting upon an object. In contrast, 10 Newton, downward is a

complete description of the force acting upon an object; both the magnitude (10 Newton) and the direction (downward) are

given.

Because a force is a vector that has a direction, it is common to represent forces using diagrams in

which a force is represented by an arrow. Such vector diagrams were introduced in an earlier unit

and are used throughout the study of physics. The size of the arrow is reflective of the magnitude of

the force and the direction of the arrow reveals the direction that the force is acting. (Such diagrams

are known as free-body diagrams and are discussed later in this lesson.) Furthermore, because

forces are vectors, the effect of an individual force upon an object is often canceled by the effect of

another force. For example, the effect of a 20-Newton upward force acting upon a book is canceled

by the effect of a 20-Newton downward force acting upon the book. In such instances, it is said that

the two individual forces balance each other; there would be no unbalanced force acting upon the

book.

Other situations could be imagined in which two of the individual vector forces cancel each other

("balance"), yet a third individual force exists that is not balanced by another force. For

example, imagine a book sliding across the rough surface of a table from left to right. The

downward force of gravity and the upward force of the table supporting the book act in opposite

directions and thus balance each other. However, the force of friction acts leftwards, and there is

no rightward force to balance it. In this case, an unbalanced force acts upon the book to change

its state of motion.

The exact details of drawing free-body diagrams are discussed later. For now, the emphasis is upon the fact that a force is a


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vector quantity that has a direction. The importance of this fact will become clear as we analyze the individual forces acting upon

an object later in this lesson.

Next Section: Types of Forces

Jump To Lesson 3: Newton's Second Law of Motion

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Types of Forces

A force is a push or pull acting upon an object as a result of its interaction with another object.

There are a variety of types of forces. Previously in this lesson, a variety of force types were

placed into two broad category headings on the basis of whether the force resulted from the contact or non-contact of the two

interacting objects.





Applied Force

Spring Force

These types of individual forces will now be discussed in more detail. To read about each force listed above, continue scrolling

through this page. Or to read about an individual force, click on its name from the list below.

Applied Force

Gravitational Force

Normal Force

Frictional Force


Tension Force

Spring Force

Type of Force

(and Symbol)

Description of Force

Applied Force

Fapp

An applied force is a force that is applied to an object by a person or another object. If a

person is pushing a desk across the room, then there is an applied force acting upon the

object. The applied force is the force exerted on the desk by the person.

Return to Top

Gravity Force

(also known as Weight)

Fgrav

The force of gravity is the force with which the earth, moon, or other massively large

object attracts another object towards itself. By definition, this is the weight of the

object. All objects upon earth experience a force of gravity that is directed "downward"

towards the center of the earth. The force of gravity on earth is always equal to the

weight of the object as found by the equation:

Fgrav = m * gwhere g = 9.8 N/kg (on Earth)

and m = mass (in kg)

(Caution: do not confuse weight with mass.)

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Normal Force

Fnorm

The normal force is the support force exerted upon an object that is in contact with

another stable object. For example, if a book is resting upon a surface, then the surface

is exerting an upward force upon the book in order to support the weight of the book.

On occasions, a normal force is exerted horizontally between two objects that are in

contact with each other. For instance, if a person leans against a wall, the wall pushes

horizontally on the person.

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Friction Force

Ffrict

The friction force is the force exerted by a surface as an object moves across it or makes

an effort to move across it. There are at least two types of friction force - sliding and

static friction. Thought it is not always the case, the friction force often opposes the

motion of an object. For example, if a book slides across the surface of a desk, then the

desk exerts a friction force in the opposite direction of its motion. Friction results from

the two surfaces being pressed together closely, causing intermolecular attractive forces


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between molecules of different surfaces. As such, friction depends upon the nature of

the two surfaces and upon the degree to which they are pressed together. The

maximum amount of friction force that a surface can exert upon an object can be

calculated using the formula below:

Ffrict = µ • Fnorm

The friction force is discussed in more detail later on this page.

Return to Top


Fair

The air resistance is a special type of frictional force that acts upon objects as they

travel through the air. The force of air resistance is often observed to oppose the motion

of an object. This force will frequently be neglected due to its negligible magnitude (and

due to the fact that it is mathematically difficult to predict its value). It is most

noticeable for objects that travel at high speeds (e.g., a skydiver or a downhill skier) or

for objects with large surface areas. Air resistance will be discussed in more detail in

Lesson 3.

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Tension Force

Ftens

The tension force is the force that is transmitted through a string, rope, cable or wire

when it is pulled tight by forces acting from opposite ends. The tension force is directed

along the length of the wire and pulls equally on the objects on the opposite ends of the

wire.

Return to Top

Spring Force

Fspring

The spring force is the force exerted by a compressed or stretched spring upon any

object that is attached to it. An object that compresses or stretches a spring is always

acted upon by a force that restores the object to its rest or equilibrium position. For

most springs (specifically, for those that are said to obey "Hooke's Law"), the magnitude

of the force is directly proportional to the amount of stretch or compression of the

spring.

Return to Top

Confusion of Mass and Weight

A few further comments should be added about the single force that is a source of much confusion to many students of physics -

the force of gravity. As mentioned above, the force of gravity acting upon an object is sometimes referred to as the weight of

the object. Many students of physics confuse weight with mass. The mass of an object refers to the amount of matter that is

contained by the object; the weight of an object is the force of gravity acting upon that object. Mass is related to how much stuff

is there and weight is related to the pull of the Earth (or any other planet) upon that stuff. The mass of an object (measured in

kg) will be the same no matter where in the universe that object is located. Mass is never altered by location, the pull of gravity,

speed or even the existence of other forces. For example, a 2-kg object will have a mass of 2 kg whether it is located on Earth,

the moon, or Jupiter; its mass will be 2 kg whether it is moving or not (at least for purposes of our study); and its mass will be 2

kg whether it is being pushed upon or not.

On the other hand, the weight of an object (measured in Newton) will vary according to where in the universe the object is.

Weight depends upon which planet is exerting the force and the distance the object is from the planet. Weight, being equivalent

to the force of gravity, is dependent upon the value of g - the gravitational field strength. On earth's surface g is 9.8 N/kg (often

approximated as 10 N/kg). On the moon's surface, g is 1.7 N/kg. Go to another planet, and there will be another g value.

Furthermore, the g value is inversely proportional to the distance from the center of the planet. So if we were to measure g at a

distance of 400 km above the earth's surface, then we would find the g value to be less than 9.8 N/kg. (The nature of the force

of gravity will be discussed in more detail in a later unit of The Physics Classroom.) Always be cautious of the distinction between

mass and weight. It is the source of much confusion for many students of physics.

Flickr Physics Photo

A 1.0-kg mass is suspended from a spring scale in an effort to determine its weight. The scale reads just short of 10.0 N - close

enough to call it 9.8 N. Mass refers to how much stuff is present in the object. Weight refers to the force with which gravity

pulls upon the object.


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Investigate!

Even on the surface of the Earth, there are local variations in the value of g that have very small effects upon an object's weight.

These variations are due to latitude, altitude and the local geological structure of the region. Use the Gravitational Fields

widget below to investigate how location affects the value of g.

Gravitational Fields

Enter a location and click on the Get g button.

Location: Chicago, IL

Get g

Sliding versus Static Friction

As mentioned above, the friction force is the force exerted by a surface as an object moves across it or makes an effort to move

across it. For the purpose of our study of physics at The Physics Classroom, there are two types of friction force - static friction

and sliding friction. Sliding friction results when an object slides across a surface. As an example, consider pushing a box

across a floor. The floor surface offers resistance to the movement of the box. We often say that the floor exerts a friction force

upon the box. This is an example of a sliding friction force since it results from the sliding motion of the box. If a car slams on its

brakes and skids to a stop (without antilock brakes), there is a sliding friction force exerted upon the car tires by the roadway

surface. This friction force is also a sliding friction force because the car is sliding across the road surface. Sliding friction forces

can be calculated from knowledge of the coefficient of friction and the normal force exerted upon the object by the surface it is

sliding across. The formula is:

Sliding Ffrict = µ • Fnorm

The symbol represents the coefficient of sliding friction between the two surfaces. The coefficient value is dependent

primarily upon the nature of the surfaces that are in contact with each other. For most surface combinations, the friction

coefficients show little dependence upon other variables such as area of contact, temperature, etc. Values of have been

experimentally determined for a variety of surface combinations and are often tabulated in technical manuals and handbooks.

The values of µ provide a measure of the relative amount of adhesion or attraction of the two surfaces for each other. The more

that surface molecules tend to adhere to each other, the greater the coefficient values and the greater the friction force.

Friction forces can also exist when the two surfaces are not sliding across each other. Such friction forces are referred to as static

friction. Static friction results when the surfaces of two objects are at rest relative to one another and a force exists on one of

the objects to set it into motion relative to the other object. Suppose you were to push with 5-Newton of force on a large box to


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move it across the floor. The box might remain in place. A static friction force exists between the surfaces of the floor and the box

to prevent the box from being set into motion. The static friction force balances the force that you exert on the box such that the

stationary box remains at rest. When exerting 5 Newton of applied force on the box, the static friction force has a magnitude of 5

Newton. Suppose that you were to push with 25 Newton of force on the large box and the box were to still remain in place. Static

friction now has a magnitude of 25 Newton. Then suppose that you were to increase the force to 26 Newton and the box finally

budged from its resting position and was set into motion across the floor. The box-floor surfaces were able to provide up to 25

Newton of static friction force to match your applied force. Yet the two surfaces were not able to provide 26 Newton of static

friction force. The amount of static friction resulting from the adhesion of any two surfaces has an upper limit. In this case, the

static friction force spans the range from 0 Newton (if there is no force upon the box) to 25 Newton (if you push on the box with

25 Newton of force). This relationship is often expressed as follows:

Ffrict-static ≤ µfrict-static• Fnorm

The symbol µfrict-static represents the coefficient of static friction between the two surfaces. Like the coefficient of sliding

friction, this coefficient is dependent upon the types of surfaces that are attempting to move across each other. In general,

values of static friction coefficients are greater than the values of sliding friction coefficients for the same two surfaces. Thus, it

typically takes more force to budge an object into motion than it does to maintain the motion once it has been started.

The meaning of each of these forces listed in the table above will have to be thoroughly understood to be successful during this

unit. Ultimately, you must be able to read a verbal description of a physical situation and know enough about these forces to

recognize their presence (or absence) and to construct a free-body diagram that illustrates their relative magnitude and

direction.


1. Complete the following table showing the relationship between mass and weight.

Object Mass (kg)Weight (N)Melon 1 kg See Answer

Apple See Answer 0.98 N

Pat

Eatladee25 kg See Answer

Fred See Answer 980 N

2. Different masses are hung on a spring scale calibrated in Newtons.

The force exerted by gravity on 1 kg = 9.8 N.a.

The force exerted by gravity on 5 kg = ______ N.b.

The force exerted by gravity on _______ kg = 98 N.c.

The force exerted by gravity on 70 kg = ________ N.d.

See Answer

3. When a person diets, is their goal to lose mass or to lose weight? Explain.

See Answer

Next Section: Drawing Free-Body Diagrams


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Drawing Free-Body Diagrams

Free-body diagrams are diagrams used to show the relative

magnitude and direction of all forces acting upon an object in

a given situation. A free-body diagram is a special example of

the vector diagrams that were discussed in an earlier unit.

These diagrams will be used throughout our study of physics.

The size of the arrow in a free-body diagram reflects the

magnitude of the force. The direction of the arrow shows the

direction that the force is acting. Each force arrow in the

diagram is labeled to indicate the exact type of force. It is

generally customary in a free-body diagram to represent the

object by a box and to draw the force arrow from the center of

the box outward in the direction that the force is acting. An

example of a free-body diagram is shown at the right.

The free-body diagram above depicts four forces acting upon the object. Objects do not necessarily always have four forces

acting upon them. There will be cases in which the number of forces depicted by a free-body diagram will be one, two, or three.

There is no hard and fast rule about the number of forces that must be drawn in a free-body diagram. The only rule for drawing

free-body diagrams is to depict all the forces that exist for that object in the given situation. Thus, to construct free-body

diagrams, it is extremely important to know the various types of forces. If given a description of a physical situation, begin by

using your understanding of the force types to identify which forces are present. Then determine the direction in which each force

is acting. Finally, draw a box and add arrows for each existing force in the appropriate direction; label each force arrow according

to its type. If necessary, refer to the list of forces and their description in order to understand the various force types and their

appropriate symbols.

Practice

Apply the method described in the paragraph above to construct free-body diagrams for the various situations described below.

Answers are shown and explained at the bottom of this page.

A book is at rest on a tabletop. Diagram the forces acting on the book. See answer.a.

A girl is suspended motionless from the ceiling by two ropes. Diagram the forces acting on the combination of girl and

bar. See answer.

b.

An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it is falling.

See answer.

c.

A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. Diagram

the forces acting on the squirrel. See answer.

d.

A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional

forces. Neglect air resistance. Diagram the forces acting on the book. See answer.

e.

A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces.

Neglect air resistance. Diagram the forces acting on the book. See answer.

f.

A college student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder.

Diagram the vertical forces acting on the backpack. See answer.

g.

A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver.

See answer.

h.

A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration. Diagram the forces

acting upon the sled. See answer.

i.

A football is moving upwards towards its peak after having been booted by the punter. Diagram the forces acting upon

the football as it rises upward towards its peak. See answer.

j.

A car is coasting to the right and slowing down. Diagram the forces acting upon the car. See answer.k.

Answers

Answers to the above exercise are shown here. If you have difficulty drawing free-body diagrams, then you ought to be

concerned. Continue to review the the list of forces and their description and this page in order to gain a comfort with

constructing free-body diagrams.


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1. A book is at rest on a tabletop. A free-body diagram for this situation looks like this:

Return to Questions

Return to Info on Free-body diagrams

Return to on-line Force Description List

2. A girl is suspended motionless from the ceiling by two ropes. A free-body diagram for this situation looks like this:

Return to Questions



3. An egg is free-falling from a nest in a tree. Neglect air resistance. A free-body diagram for this situation looks like this:

Return to Questions



4. A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. A free-body

diagram for this situation looks like this:

Return to Questions



5. A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces.

Neglect air resistance. A free-body diagram for this situation looks like this:

Return to Questions



2 of 4 9/18/2012 7:23 PM


6. A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect

air resistance. A free-body diagram for this situation looks like this:

Return to Questions



7. A college student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder. A

free-body diagram for this situation looks like this:

Return to Questions



8. A skydiver is descending with a constant velocity. Consider air resistance. A free-body diagram for this situation looks like

this:

Return to Questions



9. A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration. A free-body diagram for

this situation looks like this:

Return to Questions




3 of 4 9/18/2012 7:23 PM

10. A football is moving upwards towards its peak after having been booted by the punter. A free-body diagram for this situation

looks like this:

Return to Questions



11. A car is coasting to the right and slowing down. A free-body diagram for this situation looks like this:

Return to Questions



Next Section: Determining the Net Force


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If you have been reading through Lessons 1 and 2, then Newton's first law of motion ought to

be thoroughly understood.

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and

in the same direction unless acted upon by an unbalanced force.

In the statement of Newton's first law, the unbalanced force refers to that force that does not become completely balanced (or

canceled) by the other individual forces. If either all the vertical forces (up and down) do not cancel each other and/or all

horizontal forces do not cancel each other, then an unbalanced force exists. The existence of an unbalanced force for a given

situation can be quickly realized by looking at the free-body diagram for that situation. Free-body diagrams for three situations

are shown below. Note that the actual magnitudes of the individual forces are indicated on the diagram.

In each of the above situations, there is an unbalanced force. It is commonly said that in each situation there is a net force

acting upon the object. The net force is the vector sum of all the forces that act upon an object. That is to say, the net force is

the sum of all the forces, taking into account the fact that a force is a vector and two forces of equal magnitude and opposite

direction will cancel each other out. At this point, the rules for summing vectors (such as force vectors) will be kept relatively

simple. Observe the following examples of summing two forces:

Observe in the diagram above that a downward vector will provide a partial or full cancellation of an upward vector. And a

leftward vector will provide a partial or full cancellation of a rightward vector. The addition of force vectors can be done in the

same manner in order to determine the net force (i.e., the vector sum of all the individual forces). Consider the three situations

below in which the net force is determined by summing the individual force vectors that are acting upon the objects.

As mentioned earlier, a net force (i.e., an unbalanced force) causes an acceleration. In a previous unit, several means of

representing accelerated motion (position-time and velocity-time graphs, ticker tape diagrams, velocity-time data, etc.)

were discussed. Combine your understanding of acceleration and the newly acquired knowledge that a net force causes an

acceleration to determine whether or not a net force exists in the following situations. Click on the button to view the answers.


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Description of Motion Net Force: Yes or No?

See Answer

See Answer

See Answer

See Answer

See Answer

See Answer


1. Free-body diagrams for four situations are shown below. For each situation, determine the net force acting upon the object.

Click the buttons to view the answers.

See Answer to Situation A

See Answer to Situation B

See Answer to Situation C

See Answer to Situation D

2. Free-body diagrams for four situations are shown below. The net force is known for each situation. However, the magnitudes of

a few of the individual forces are not known. Analyze each situation individually and determine the magnitude of the unknown

forces. Then click the button to view the answers.


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See Answer


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Newton's Second Law of Motion

Newton's Second Law | The Big Misconception | Finding Acceleration

Finding Individual Forces | Free Fall and Air Resistance | Double Trouble

Newton's Second Law

Newton's first law of motion predicts the behavior of objects for which all existing forces are

balanced. The first law - sometimes referred to as the law of inertia - states that if the forces

acting upon an object are balanced, then the acceleration of that object will be 0 m/s/s. Objects at equilibrium (the condition in

which all forces balance) will not accelerate. According to Newton, an object will only accelerate if there is a net or unbalanced

force acting upon it. The presence of an unbalanced force will accelerate an object - changing its speed, its direction, or both its

speed and direction.

Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law

states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of

the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass

of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object

is increased, the acceleration of the object is decreased.

Newton's second law of motion can be formally stated as follows:

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force,

in the same direction as the net force, and inversely proportional to the mass of the object.

This verbal statement can be expressed in equation form as follows:

a = Fnet / m

The above equation is often rearranged to a more familiar form as shown below. The net force is equated to the product of the

mass times the acceleration.

Fnet = m * a

In this entire discussion, the emphasis has been on the net force. The acceleration is directly proportional to

the net force; the net force equals mass times acceleration; the acceleration in the same direction as the net

force; an acceleration is produced by a net force. The NET FORCE. It is important to remember this distinction.

Do not use the value of merely "any 'ole force" in the above equation. It is the net force that is related to

acceleration. As discussed in an earlier lesson, the net force is the vector sum of all the forces. If all the

individual forces acting upon an object are known, then the net force can be determined. If necessary, review

this principle by returning to the practice questions in Lesson 2.

Consistent with the above equation, a unit of force is equal to a unit of mass times a unit of acceleration. By substituting

standard metric units for force, mass, and acceleration into the above equation, the following unit equivalency can be written.

The definition of the standard metric unit of force is stated by the above equation. One Newton is defined as the amount of force


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required to give a 1-kg mass an acceleration of 1 m/s/s.

The Fnet = m • a equation is often used in algebraic problem solving. The table below can be filled by substituting into the

equation and solving for the unknown quantity. Try it yourself and then use the click on the buttons to view the answers.

Net Force

(N)

Mass

(kg)

Acceleration

(m/s/s)1. 10 2 See Answer

2. 20 2 See Answer

3. 20 4 See Answer

4. See Answer 2 5

5. 10 See Answer 10

The numerical information in the table above demonstrates some important qualitative relationships between force, mass, and

acceleration. Comparing the values in rows 1 and 2, it can be seen that a doubling of the net force results in a doubling of the

acceleration (if mass is held constant). Similarly, comparing the values in rows 2 and 4 demonstrates that a halving of the net

force results in a halving of the acceleration (if mass is held constant). Acceleration is directly proportional to net force.

Furthermore, the qualitative relationship between mass and acceleration can be seen by a comparison of the numerical values in

the above table. Observe from rows 2 and 3 that a doubling of the mass results in a halving of the acceleration (if force is held

constant). And similarly, rows 4 and 5 show that a halving of the mass results in a doubling of the acceleration (if force is held

constant). Acceleration is inversely proportional to mass.

The analysis of the table data illustrates that an equation such as Fnet = m*a can be a guide to thinking about how a variation in

one quantity might effect another quantity. Whatever alteration is made of the net force, the same change will occur with the

acceleration. Double, triple or quadruple the net force, and the acceleration will do the same. On the other hand, whatever

alteration is made of the mass, the opposite or inverse change will occur with the acceleration. Double, triple or quadruple the

mass, and the acceleration will be one-half, one-third or one-fourth its original value.

As stated above, the direction of the net force is in the same direction as the acceleration. Thus, if the direction of the

acceleration is known, then the direction of the net force is also known. Consider the two oil drop diagrams below for an

acceleration of a car. From the diagram, determine the direction of the net force that is acting upon the car. Then click the

buttons to view the answers. (If necessary, review acceleration from the previous unit.)

See Answer

See Answer

In conclusion, Newton's second law provides the explanation for the behavior of objects upon which the forces do not balance.

The law states that unbalanced forces cause objects to accelerate with an acceleration that is directly proportional to the net force

and inversely proportional to the mass.

Rocket Science!

NASA rockets (and others) accelerate upward off the launch pad as they burn a tremendous amount of fuel. As the fuel is burned

and exhausted to propel the rocket, the mass of the rocket changes. As such, the same propulsion force can result in increasing

acceleration values over time. Use the Rocket Science widget below to explore this effect.

Rocket Science

Determines the speed of a rocket as a function of time

if given the initial mass and the exhaust velocity.

Show Me the Science

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1. Determine the accelerations that result when a 12-N net force is applied to a 3-kg object and then to a 6-kg object.

See Answer

2. A net force of 15 N is exerted on an encyclopedia to cause it to accelerate at a rate of 5 m/s2. Determine the mass of the

encyclopedia.

See Answer

3. Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is doubled, then what is the

new acceleration of the sled?

See Answer

4. Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is halved, then what is the new

acceleration of the sled?

See Answer

Next Section: The Big Misconception

Jump To Lesson 4: Newton's Third Law of Motion

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The Big Misconception

So what's the big deal? Many people have known Newton's first law

since eighth grade (or earlier). And if prompted with the first few words,

most people could probably recite the law word for word. And what is so

terribly difficult about remembering that F = ma? It seems to be a

simple algebraic statement for solving story problems. The big deal

however is not the ability to recite the first law nor to use the second

law to solve problems; but rather the ability to understand their

meaning and to believe their implications. While most people know

what Newton's laws say, many people do not know what they mean (or

simply do not believe what they mean).

Cognitive scientists (scientists who study how people learn) have shown that physics students come into

physics class with a set of beliefs that they are unwilling (or not easily willing) to discard despite evidence

to the contrary. These beliefs about motion (known as misconceptions) hinder further learning. The task of

overcoming misconceptions involves becoming aware of the misconceptions, considering alternative

conceptions or explanations, making a personal evaluation of the two competing ideas and adopting a new

conception that is more reasonable than the previously held-misconception. This process involves

self-reflection (to ponder your own belief systems), critical thinking (to analyze the reasonableness of two

competing ideas), and evaluation (to select the most reasonable and harmonious model that explains the

world of motion). Self-reflection, critical thinking, and evaluation. While this process may seem terribly complicated, it is simply

a matter of using your noodle (that's your brain).

The most common misconception is one that dates back for ages; it is the idea that sustaining

motion requires a continued force. The misconception has already been discussed in a previous

lesson, but will now be discussed in more detail. This misconception sticks out its ugly head in a

number of different ways and at a number of different times. As your read through the following

discussion, give careful attention to your own belief systems. View physics as a system of

thinking about the world rather than information that can be dumped into your brain without

evaluating its consistency with your own belief systems.

Newton's laws declare loudly that a net force (an unbalanced force) causes an acceleration; the

acceleration is in the same direction as the net force. To test your own belief system, consider the

following question and its answer as seen by clicking the button.

Are You Infected with the Misconception?

Two students are discussing their physics homework prior to class. They are discussing an object that is being

acted upon by two individual forces (both in a vertical direction); the free-body diagram for the particular

object is shown at the right. During the discussion, Anna Litical suggests to Noah Formula that the object

under discussion could be moving. In fact, Anna suggests that if friction and air resistance could be ignored

(because of their negligible size), the object could be moving in a horizontal direction. According to Anna, an

object experiencing forces as described at the right could be experiencing a horizontal motion as described

below.

Noah Formula objects, arguing that the object could not have any horizontal motion if there are only vertical forces acting upon

it. Noah claims that the object must be at rest, perhaps on a table or floor. After all, says Noah, an object experiencing a balance

of forces will be at rest. Who do you agree with?

See Answer

Remember last winter when you went sledding down the hill and across the level surface at the local park? (Apologies are

extended to those who live in warmer winter climates.)

Imagine a the moment that there was no friction along the level surface from point B to point C and


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that there was no air resistance to impede your motion. How far would your sled travel? And what

would its motion be like? Most students I've talked to quickly answer: the sled would travel forever at

constant speed. Without friction or air resistance to slow it down, the sled would continue in motion

with the same speed and in the same direction. The forces acting upon the sled from point B to point C

would be the normal force (the snow pushes up on the sled) and the gravity force (see diagram at

right). These forces are balanced and since the sled is already in motion at point B it will continue in

motion with the same speed and direction. So, as in the case of the sled and as in the case of the

object that Noah and Anna are discussing, an object can be moving to the right even if the only forces

acting upon the object are vertical forces. Forces do not cause motion; forces cause accelerations.

Newton's first law of motion declares that a force is not needed to keep an object in motion. Slide a book across a table and

watch it slide to a rest position. The book in motion on the table top does not come to a rest position because of the absence of a

force; rather it is the presence of a force - that force being the force of friction - that brings the book to a rest position. In the

absence of a force of friction, the book would continue in motion with the same speed and direction - forever (or at least to the

end of the table top)! A force is not required to keep a moving book in motion; and a force is not required to keep a moving sled

in motion; and a force is not required to keep any object horizontally moving object in motion. To read more about this

misconception, return to an earlier lesson.

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Finding Acceleration

As learned earlier in Lesson 3 (as well as in Lesson 2), the net force is the vector sum of all the

individual forces. In Lesson 2, we learned how to determine the net force if the magnitudes of all

the individual forces are known. In this lesson, we will learn how to determine the acceleration of an object if the magnitudes of

all the individual forces are known. The three major equations that will be useful are the equation for net force (Fnet = m•a), the

equation for gravitational force (Fgrav = m•g), and the equation for frictional force (Ffrict = µ•Fnorm).

The process of determining the acceleration of an object demands that the mass and the net force are known. If mass (m) and

net force (Fnet) are known, then the acceleration is determined by use of the equation.

Thus, the task involves using the above equations, the given information, and your understanding of Newton's laws to determine

the acceleration. To gain a feel for how this method is applied, try the following practice problems. Once you have solved the

problems, click the button to check your answers.

Practice #1

An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of

friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air

resistance.)

See Answer

Practice #2

An applied force of 20 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of

friction. Use the diagram to determine the normal force, the net force, the coefficient of friction (µ) between the object and the

surface, the mass, and the acceleration of the object. (Neglect air resistance.)

See Answer

Practice #3

A 5-kg object is sliding to the right and encountering a friction force that slows it down. The coefficient of friction (µ) between

the object and the surface is 0.1. Determine the force of gravity, the normal force, the force of friction, the net force, and the


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acceleration. (Neglect air resistance.)

See Answer

A couple more practice problems are provided below. You should make an effort to solve as many problems as you

can without the assistance of notes, solutions, teachers, and other students. Commit yourself to individually solving

the problems. In the meantime, an important caution is worth mentioning:

Avoid forcing a problem into the form of a previously solved problem. Problems in physics will seldom look the

same. Instead of solving problems by rote or by mimicry of a previously solved problem, utilize your conceptual

understanding of Newton's laws to work towards solutions to problems. Use your understanding of weight and mass to

find the m or the Fgrav in a problem. Use your conceptual understanding of net force (vector sum of all the forces) to

find the value of Fnet or the value of an individual force. Do not divorce the solving of physics problems from your

understanding of physics concepts. If you are unable to solve physics problems like those above, it is does not

necessarily mean that you are having math difficulties. It is likely that you are having a physics concepts difficulty.


1. Edwardo applies a 4.25-N rightward force to a 0.765-kg book to accelerate it across a tabletop. The coefficient of friction

between the book and the tabletop is 0.410. Determine the acceleration of the book.

See Answer

2. In a physics lab, Kate and Rob use a hanging mass and pulley system to exert a 2.45 N rightward force on a 0.500-kg cart to

accelerate it across a low-friction track. If the total resistance force to the motion of the cart is 0.72 N, then what is the cart's

acceleration?

See Answer

Next Section: Finding Individual Forces


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Finding Individual Forces

As learned earlier in Lesson 3 (as well as in Lesson 2), the net force is the vector sum of all the

individual forces. In Lesson 2, we learned how to determine the net force if the magnitudes of all

the individual forces are known. In this lesson, we will learn how to determine the magnitudes of all the individual forces if the

mass and acceleration of the object are known. The three major equations that will be useful are the equation for net force (Fnet

= m•a), the equation for gravitational force (Fgrav = m•g), and the equation for frictional force (Ffrict = µ•Fnorm).

The process of determining the value of the individual forces acting upon an object involve an application of Newton's second law

(Fnet=m•a) and an application of the meaning of the net force. If mass (m) and acceleration (a) are known, then the net force

(Fnet) can be determined by use of the equation.

Fnet = m • a

If the numerical value for the net force and the direction of the net force is known, then the value of all individual forces can be

determined. Thus, the task involves using the above equations, the given information, and your understanding of net force to

determine the value of individual forces. To gain a feel for how this method is applied, try the following practice problems. The

problems progress from easy to more difficult. Once you have solved a problem, click the button to check your answers.

Practice #1

Free-body diagrams for four situations are shown below. The net force is known for each situation. However, the magnitudes of a

few of the individual forces are not known. Analyze each situation individually and determine the magnitude of the unknown

forces.

See Answer

Practice #2

A rightward force is applied to a 6-kg object to move it across a rough surface at constant velocity. The object encounters 15 N of

frictional force. Use the diagram to determine the gravitational force, normal force, net force, and applied force. (Neglect air

resistance.)

See Answer

Practice #3

A rightward force is applied to a 10-kg object to move it across a rough surface at constant velocity. The coefficient of friction

between the object and the surface is 0.2. Use the diagram to determine the gravitational force, normal force, applied force,

frictional force, and net force. (Neglect air resistance.)


Finding Individual Forces http://www.physicsclassroom.com/Class/newtlaws/u2l3d.cfm

1 of 3 9/18/2012 7:26 PM

See Answer

Practice #4

A rightward force is applied to a 5-kg object to move it across a rough surface with a rightward acceleration of 2 m/s/s. The

coefficient of friction between the object and the surface is 0.1. Use the diagram to determine the gravitational force, normal

force, applied force, frictional force, and net force. (Neglect air resistance.)

See Answer

Practice #5

A rightward force of 25 N is applied to a 4-kg object to move it across a rough surface with a rightward acceleration of 2.5 m/s/s.

Use the diagram to determine the gravitational force, normal force, frictional force, net force, and the coefficient of friction

between the object and the surface. (Neglect air resistance.)

See Answer

A couple more practice problems are provided below. You should make an effort to solve as many problems as you

can without the assistance of notes, solutions, teachers, and other students. Commit yourself to individually solving

the problems. In the meantime, an important caution is worth mentioning:

Avoid forcing a problem into the form of a previously solved problem. Problems in physics will seldom look the

same. Instead of solving problems by rote or by mimicry of a previously solved problem, utilize your conceptual


2 of 3 9/18/2012 7:26 PM

understanding of Newton's laws to work towards solutions to problems. Use your understanding of weight and mass to

find the m or the Fgrav in a problem. Use your conceptual understanding of net force (vector sum of all the forces) to

find the value of Fnet or the value of an individual force. Do not divorce the solving of physics problems from your

understanding of physics concepts. If you are unable to solve physics problems like those above, it is does not

necessarily mean that you are having math difficulties. It is likely that you are having a physics concepts difficulty.


1. Lee Mealone is sledding with his friends when he becomes disgruntled by one of his friend's comments. He exerts a rightward

force of 9.13 N on his 4.68-kg sled to accelerate it across the snow. If the acceleration of the sled is 0.815 m/s/s, then what is

the coefficient of friction between the sled and the snow?

See Answer

2. In a Physics lab, Ernesto and Amanda apply a 34.5 N rightward force to a 4.52-kg cart to accelerate it across a horizontal

surface at a rate of 1.28 m/s/s. Determine the friction force acting upon the cart.

See Answer

Next Section: Free Fall and Air Resistance


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Free Fall and Air Resistance

In a previous unit, it was stated that all objects (regardless of their mass) free fall with the

same acceleration - 9.8 m/s/s. This particular acceleration value is so important in physics that

it has its own peculiar name - the acceleration of gravity - and its own peculiar symbol - g. But why do all objects free fall at the

same rate of acceleration regardless of their mass? Is it because they all weigh the same? ... because they all have the same

gravity? ... because the air resistance is the same for each? Why? These questions will be explored in this section of Lesson 3.

In addition to an exploration of free fall, the motion of objects that encounter air resistance will also be analyzed. In particular,

two questions will be explored:

Why do objects that encounter air resistance ultimately reach a terminal velocity?

In situations in which there is air resistance, why do more massive objects fall faster than less massive objects?

To answer the above questions, Newton's second law of motion (Fnet = m•a) will be applied to analyze the motion of objects that

are falling under the sole influence of gravity (free fall) and under the dual influence of gravity and air resistance.

Free Fall Motion

As learned in an earlier unit, free fall is a special type of motion in which the only force acting upon an object is gravity. Objects

that are said to be undergoing free fall, are not encountering a significant force of air resistance; they are falling under the sole

influence of gravity. Under such conditions, all objects will fall with the same rate of acceleration, regardless of their mass. But

why? Consider the free-falling motion of a 1000-kg baby elephant and a 1-kg overgrown mouse.

If Newton's second law were applied to their falling motion, and if a free-body diagram were

constructed, then it would be seen that the 1000-kg baby elephant would experiences a greater

force of gravity. This greater force of gravity would have a direct affect upon the elephant's

acceleration; thus, based on force alone, it might be thought that the 1000-kg baby elephant would

accelerate faster. But acceleration depends upon two factors: force and mass. The 1000-kg baby

elephant obviously has more mass (or inertia). This increased mass has an inverse affect upon the

elephant's acceleration. And thus, the direct affect of greater force on the 1000-kg elephant is

offset by the inverse affect of the greater mass of the 1000-kg elephant; and so each object

accelerates at the same rate - approximately 10 m/s/s. The ratio of force to mass (Fnet/m) is the

same for the elephant and the mouse under situations involving free fall.

This ratio (Fnet/m) is sometimes called the gravitational field strength and is expressed as 9.8

N/kg (for a location upon Earth's surface). The gravitational field strength is a property of the

location within Earth's gravitational field and not a property of the baby elephant nor the mouse. All

objects placed upon Earth's surface will experience this amount of force (9.8 N) upon every 1

kilogram of mass within the object. Being a property of the location within Earth's gravitational field and not a property of the

free falling object itself, all objects on Earth's surface will experience this amount of force per mass. As such, all objects free fall

at the same rate regardless of their mass. Because the 9.8 N/kg gravitational field at Earth's surface causes a 9.8 m/s/s

acceleration of any object placed there, we often call this ratio the acceleration of gravity. (Gravitational forces will be discussed

in greater detail in a later unit of The Physics Classroom tutorial.)


Free Fall and Air Resistance http://www.physicsclassroom.com/Class/newtlaws/u2l3e.cfm

1 of 4 9/18/2012 7:27 PM

Look It Up!

The value of the gravitational field strength (g) is different in different gravitational environments. Use the Value of g widget

below to look up the the gravitational field strength on other planets. Select a location from the pull-down menu; then click the

Submit button.

Value of g

What is the acceleration of gravity on (in m/s/s)?

Submit

See http://www.physicsclassroom.com/Class/circles/u6l3e.cfm.

Investigate!

Even on the surface of the Earth, there are local variations in the value of g. These variations are due to latitude (the Earth isn't a

perfect sphere; it buldges in the middle), altitude and the local geological structure of the region. Use the Gravitational Fields

widget below to investigate how location affects the value of g.

Gravitational Fields

Enter a location and click on the Get g button.

Location: Chicago, IL

Get g

Falling with Air Resistance

As an object falls through air, it usually encounters some degree of air resistance. Air resistance is the

result of collisions of the object's leading surface with air molecules. The actual amount of air resistance

encountered by the object is dependent upon a variety of factors. To keep the topic simple, it can be said

that the two most common factors that have a direct affect upon the amount of air resistance are the

speed of the object and the cross-sectional area of the object. Increased speeds result in an increased

amount of air resistance. Increased cross-sectional areas result in an increased amount of air resistance.

Why does an object that encounters air resistance eventually reach a terminal velocity? To answer this questions, Newton's

second law will be applied to the motion of a falling skydiver.

In the diagrams below, free-body diagrams showing the forces acting upon an 85-kg skydiver (equipment included) are

shown. For each case, use the diagrams to determine the net force and acceleration of the skydiver at each instant in

time. Then use the button to view the answers.

moon


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See Answer to A

See Answer to B

See Answer to C

See Answer to D

The diagrams above illustrate a key principle. As an object falls, it picks up speed. The increase in speed leads to an increase in

the amount of air resistance. Eventually, the force of air resistance becomes large enough to balances the force of gravity. At this

instant in time, the net force is 0 Newton; the object will stop accelerating. The object is said to have reached a terminal

velocity. The change in velocity terminates as a result of the balance of forces. The velocity at which this happens is called the

terminal velocity.

In situations in which there is air resistance, more massive objects fall faster than less massive objects. But why? To answer the

why question, it is necessary to consider the free-body diagrams for objects of different mass. Consider the falling motion of two

skydivers: one with a mass of 100 kg (skydiver plus parachute) and the other with a mass of 150 kg (skydiver plus parachute).

The free-body diagrams are shown below for the instant in time in which they have reached terminal velocity.

As learned above, the amount of air resistance depends upon the speed of the object. A falling object will continue to accelerate

to higher speeds until they encounter an amount of air resistance that is equal to their weight. Since the 150-kg skydiver weighs

more (experiences a greater force of gravity), it will accelerate to higher speeds before reaching a terminal velocity. Thus, more

massive objects fall faster than less massive objects because they are acted upon by a larger force of gravity; for this reason,

they accelerate to higher speeds until the air resistance force equals the gravity force.

Investigate!

The amount of air resistance an object experiences depends on its speed, its cross-sectional area, its shape and the density of

the air. Air densities vary with altitude, temperature and humidity. Nonetheless, 1.29 kg/m3 is a very reasonable value. The

shape of an object effects the drag coefficient (Cd). Values for various shapes can be found here. Use the What a Drag! widget

below to explore the dependence of the air resistance force upon these four variables.

What a Drag!


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Enter values of mass density, object speed, drag coefficient and

cross-sectional area. Then click on Determine Drag Force button.

Mass Density (kg/m^3) 1.29

Object Speed (m/s) 50.0

Drag Coefficient 0.50

X-sectional Area (m^2) 0.800

Determine Drag Foce

Next Section: Double Trouble (a.k.a., Two Body Problems)


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Circular Motion and

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Current Electricity

Waves




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Double Trouble (a.k.a., Two Body Problems)

Our study thus far has been restricted to the analysis of single objects moving under the

influence of Newton's laws. But what happens if there are two objects connected together in one

way or another? For instance, there could be a tow truck hauling a car down a highway. How is such an analysis conducted? How

is the acceleration of the tow truck and the car determined? What about the force acting between the tow truck and the car? In

this part of Lesson 3, we will make an attempt to analyze such situations. We will find that the analysis is conducted in the same

general manner as when there is one object - through the use of free-body diagrams and Newton's laws.

Situations involving two objects are often referred to as two-body situations. When appearing as physics problems, two-body

problems are characterized by a set of two unknown quantities. Most commonly (though not always the case), the two

unknowns are the acceleration of the two objects and the force transmitted between the two objects. Two body-problems can

typically be approached using one of two basic approaches. One approach involves a combination of a system analysis and an

individual body analysis. In the system analysis, the two objects are considered to be a single object moving (or accelerating)

together as a whole. The mass of the system is the sum of the mass of the two individual objects. If acceleration is involved, the

acceleration of the system is the same as that of the individual objects. A system analysis is usually performed to determine

the acceleration of the system. The system analysis is combined with an individual object analysis. In the individual object

analysis, either one of the two objects is isolated and considered as a separate, independent object. A free-body diagram is

constructed and the individual forces acting upon the object are identified and calculated. An individual object analysis is usually

performed in order to determine the value of any force which acts between the two objects - for example, contact forces or

tension forces.

The dual combination of a system analysis and an individual object analysis is one of two approaches that are typically used to

analyze two-body problems. A second approach involves the use of two separate individual object analyses. In such an approach,

free-body diagrams are constructed independently for each object and Newton's second law is used to relate the individual force

values to the mass and acceleration. Each individual object analysis generates an equation with an unknown. The result is a

system of two equations with two unknowns. The system of equations is solved in order to determine the unknown values.

As a first example of the two approaches to solving two-body problems, consider the following example problem.

Example Problem 1:

A 5.0-kg and a 10.0-kg box are touching each other. A 45.0-N horizontal force is applied to the 5.0-kg

box in order to accelerate both boxes across the floor. Ignore friction forces and determine the

acceleration of the boxes and the force acting between the boxes.

The first approach to this problem involves the dual combination of a system analysis and an individual object analysis. As

mentioned, the system analysis is used to determine the acceleration and the individual object analysis is used to determine the

forces acting between the objects. In the system analysis, the two objects are considered to be a single

object. The dividing line that separates the objects is ignored. The mass of the system of two objects is

15.0 kg. The free-body diagram for the system is shown at the right. There are three forces acting upon

the system - the gravity force (the Earth pulls down on the 15.0 kg of mass), the normal force (the floor

pushes up on the system to support its weight), and the applied force (the hand is pushing on the back

part of the system). The force acting between the 5.0-kg box and the 10.0-kg box is not considered in

the system analysis since it is an internal force. Just as the forces holding atoms together within an

object are not included in a free-body diagram, so the forces holding together the parts of a system are

ignored. These are considered internal forces; only external forces are considered when drawing free-body diagrams. The

magnitude of the force of gravity is m•g or 147 N. The magnitude of the normal force is also 147 N since it must support the

weight (147 N) of the system. The applied force is stated to be 45.0 N. Newton's second law (a = Fnet/m) can be used to

determine the acceleration. Using 45.0 N for Fnet and 15.0 kg for m, the acceleration is 3.0 m/s2.

Now that the acceleration has been determined, an individual object analysis can be performed on either object in order to

determine the force acting between them. It does not matter which object is chosen; the result will be the

same in either case. Here the individual object analysis is conducted on the 10.0 kg object (only because

there is one less force acting on it). The free-body diagram for the 10.0-kg object is shown at the right.

There are only three forces acting upon it - the force of gravity on the 10.0-kg, the support force (from the

floor pushing upward) and the rightward contact force (Fcontact). As the 5.0-kg object accelerates to the

right, it will be pushing rightward upon the 10.0-kg object; this is known as a contact force (or a normal

force or an applied force or …). The vertical forces balance each other since there is no vertical

acceleration. The only unbalanced force on the 10.0-kg object is the Fcontact. This force is the net force and is equal to m•a

where m is equal to 10.0 kg (since this analysis is for the 10.0-kg object) and a was already determined to be 3.0 m/s2. The net

force is equal to 30.0 N. This net force is the force of the 5.0-kg object pushing the 10.0-kg object to the right; it has a

magnitude of 30.0 N. So the answers to the two unknowns for this problem are 3.0 m/s2 and 30.0 N.

Now we will consider the solution to this same problem using the second approach - the use of two individual object analyses. In

the process of this second approach, we will ignore the fact that we know what the answers are and presume that we are solving

the problem for the first time. In this approach, two separate free-body diagram analyses are performed. The diagrams below

show the free-body diagrams for the two objects.


Double Trouble (a.k.a., Two Body Problems) http://www.physicsclassroom.com/Class/newtlaws/u2l3f.cfm

1 of 5 9/18/2012 7:28 PM

Note that there are four forces on the 5.0-kg object at the rear. The two vertical forces - Fgrav and Fnorm - are obvious forces. The

45.0-N applied force (Fapp) is the result of the hand pushing on the rear object as described in the problem statement and

depicted in the diagram. The leftward contact force on the 5.0-kg object is the force of the 10.0-kg object pushing leftward on

the 5.0-kg object. As an attempt is made to push the rear object (5.0-kg object) forward, the front object (10.0-kg object)

pushes back upon it. This force is equal to and opposite of the rear object pushing forward on the front object. This force is

simply labeled as Fcontact for both of the free-body diagrams. In the free-body diagram for the 10.0-kg object, there are only

three forces. Once more, the two vertical forces - Fgrav and Fnorm - are obvious forces. The horizontal force is simply the 5.0-kg

object pushing the 10.0-kg object forward. The 45.0 N applied force is not exerted upon this 10.0-kg object; it is exerted on the

5.0-kg object and has already been considered in the previous free-body diagram.

Now the goal of this approach is to generate system of two equations capable of solving for the two unknown values. Using Fnet =

m•a with the free-body diagram for the 5.0-kg object will yield the Equation 1 below:

45.0 - Fcontact = 5.0•a

Using Fnet = m•a with the free-body diagram for the 10.0-kg object will yield the Equation 2 below:

Fcontact = 10.0•a

(Note that the units have been dropped from Equations 1 and 2 in order to clean the equations up.) If the

expression 10.0•a is substituted into Equation 1 for Fcontact, then Equation 1 becomes reduced to a single equation with a single

unknown. The equation becomes

45.0 - 10.0•a = 5.0•a

A couple of steps of algebra lead to an acceleration value of 3.0 m/s2. This value of a can be substituted back into Equation 2 in

order to determine the contact force:

Fcontact = 10.0•a = 10.0 •3.0

Fcontact = 30.0 N

As can be seen, using the second approach to solve two body problems yields the same two answers for the two unknowns. Now

we will try the same two approaches on a very similar problem that includes a friction force.

Example Problem 2:

A 5.0-kg and a 10.0-kg box are touching each other. A 45.0-N horizontal force is applied to the 5.0-kg

box in order to accelerate both boxes across the floor. The coefficient of kinetic friction is 0.200.

Determine the acceleration and the contact force.

Our first solution to this problem will involve the dual combination of a system analysis and an individual

object analysis. As you likely noticed, Example Problem 2 is similar to Example Problem 1 with the

exception that the surface is not frictionless in Example Problem 2. So when conducting the system

analysis in this second example, the friction on the 15-kg system must be considered. So the free-body

diagram for the system now includes four forces - the same three as in Example Problem 1 plus a

leftward force of friction. The force of friction on the system can be calculated as µ•Fnorm where Fnormis

the normal force experienced by the system. The Fnorm of the system is equal to the force of gravity

acting upon the 15.0-kg system; this value is 147 N. So

Ffrict = µ•Fnorm = (0.200)•(147 N) = 29.4 N

The vertical forces balance each other - consistent with the fact that there is no vertical acceleration. The horizontal forces do not

balance each other. The net force can be determined as the vector sum of Fapp and Ffrict. That is, Fnet = 45.0 N, right + 29.4 N,

left; these add to 15.6 N, right. The acceleration can now be calculated using Newton's second law.

a = Fnet / m = (15.6 N/15.0 kg) = 1.04 m/s2

Now that the system analysis has been used to determine the acceleration, an individual object analysis

can be performed on either object in order to determine the force acting between them. Once more, it

does not matter which object is chosen; the result would be the same in either case. The 10.0-kg object is

chosen for the individual object analysis because there is one less force acting upon it; this makes the

solution easier. There are four forces acting upon the 10.0-kg object. The two vertical forces are obvious -

the force of gravity (98.0 N) and the normal force (equal to the force of gravity). The horizontal forces are

the friction force to the left and the force of the 5.0-kg object pushing the 10.0-kg object forward; this is

labeled as Fcontact on the free-body diagram. The net force - vector sum of all the forces - can always be found by adding the

forces in the direction of the acceleration and subtracting those that are in the opposite direction. This Fnet is equal to Fcontact -

Ffrict. Applying Newton's second law to this object yields the equation:

Fcontact - Ffrict = (10.0 kg)•(1.04 m/s2)

The friction force on this 10.0-kg object is not the same as the friction force on the system (since the system was weightier). The


2 of 5 9/18/2012 7:28 PM

Ffrict value can be computed as µ•Fnorm where Fnorm is the normal force experienced by the 10.0-kg object. The Fnormof the

10.0-kg is equal to the force of gravity acting upon the 10.0-kg object; this value is 98.0 N. So

Ffrict = µ•Fnorm = (0.200)•(98.0 N) = 19.6 N

So now the value of 19.6 N can be substituted into the above equation and Fcontact can be calculated:

Fcontact - 19.6 N = (10.0 kg)•(1.04 m/s2)

Fcontact = (10.0 kg)•(1.04 m/s2) + 19.6 N

Fcontact = 30.0 N

So using the dual combination of the system analysis and individual body analysis allows us to determine the two unknown

values - 1.04 m/s2 for the acceleration and 30.0 N for the Fcontact. Now we will see how two individual object analyses can be

combined to generate a system of two equations capable of solving for the two unknowns. Once more we will start the analysis

by presuming that we are solving the problem for the first time and do not know the acceleration nor the contact force. The

free-body diagrams for the individual objects are shown below.

There are now five forces on the 5.0-kg object at the rear. The two vertical forces - Fgrav and Fnorm - are obvious forces. The

45.0-N applied force (Fapp) is the result of the hand pushing on the rear object. The leftward contact force on the 5.0-kg object is

the force of the 10.0-kg object pushing leftward on the 5.0-kg object. Its value is the same as the contact force that is exerted

on the front 10.0-kg object by the rear 5.0-kg object. This force is simply labeled as Fcontact for both of the free-body diagrams.

Finally, the leftward friction force is the result of friction with the floor over which the 5.0-kg object moves. In the free-body

diagram for the 10.0-kg object, there are now four forces. The two vertical forces - Fgrav and Fnorm - are obvious. The rightward

contact force (Fcontact) is simply the 5.0-kg object pushing the 10.0-kg object forward. And the leftward friction force is the

result of friction with the floor. Once more, the 45.0 N applied force is not exerted upon this 10.0-kg object; it is exerted on the

5.0-kg object and has already been considered in the previous free-body diagram. The friction force for each object can be

determined as µ•Fnorm where Fnorm is the normal force experienced by the individual objects. Each object experiences a

normal force equal to its weight (since vertical forces must balance). So the friction forces for the 5.0-kg object (49.0 N weight)

and 10.0-kg object (98.0 N weight) are 0.200•49.0 N and 0.200•98.0 N, respectively.

Using these Ffrict values and Newton's second law, a system of two equations capable of solving for the two unknown values can

be written. Using Fnet = m•a with the free-body diagram for the 5.0-kg object will yield Equation 3 below:

45.0 - Fcontact - 9.8 = 5.0•a

Using Fnet = m•a with the free-body diagram for the 10.0-kg object will yield the Equation 4 below:

Fcontact - 19.6 = 10.0•a

(Note that the units have been dropped from Equations 3 and 4 in order to clean the equations up.) From

Equation 4, Fcontact = 10.0•a + 19.6. Substituting this expression for Fcontact into Equation 3 and performing proper algebraic

manipulations yields the acceleration value:

45.0 - (10.0•a + 19.6) - 9.8 = 5.0•a

45.0 - 19.6 - 9.8 = 15.0•a

15.6 = 15.0•a

a = (15.6/15.0)= 1.04 m/s2

This acceleration value can be substituted back into the expression for Fcontact in order to determine the contact force:

Fcontact = 10.0•a + 19.6 = 10.0•(1.04) + 19.6

Fcontact = 30.0 N

Again we find that the second approach of using two individual object analyses yields the same set of answers for the two

unknowns. The final example problem will involve a vertical motion. The approaches will remain the same.

Example Problem 3:

A man enters an elevator holding two boxes - one on top of the other. The top box has a mass

of 6.0 kg and the bottom box has a mass of 8.0 kg. The man sets the two boxes on a metric

scale sitting on the floor. When accelerating upward from rest, the man observes that the

scale reads a value of 166 N; this is the upward force upon the bottom box. Determine the

acceleration of the elevator (and boxes) and determine the forces acting between the boxes.

Both approaches will be used to solve this problem. The first approach involves the dual combination

of a system analysis and an individual object analysis. For the system analysis, the two boxes are

considered to be a single system with a mass of 14.0 kg. There are two forces acting upon this

system - the force of gravity and the normal force. The free-body diagram is shown at the right. The

force of gravity is calculated in the usual manner using 14.0 kg as the mass.

Fgrav = m•g = 14.0 kg • 9.8 N/kg = 137.2 N

Since there is a vertical acceleration, the vertical forces will not be balanced; the Fgrav is not equal to


3 of 5 9/18/2012 7:28 PM

the Fnorm value. The normal force is provided in the problem statement. This 166-N normal force is the upward force exerted

upon the bottom box; it serves as the force on the system since the bottom box is part of the system. The net force is the vector

sum of these two forces. So

Fnet = 166 N, up + 137.2 N, down = 28.8 N, up

The acceleration can be calculated using Newton's second law:

a = Fnet /m = 28.8 N/14.0 kg = 2.0571 m/s2 = ~2.1 m/s2

Now that the system analysis has been used to determine the acceleration, an individual object

analysis can be performed on either box in order to determine the force acting between them. As in the

previous problems, it does not matter which box is chosen; the result will be the same in either case.

The top box is used in this analysis since it encounters one less force. The free-body diagram is shown

at the right. The force of gravity on the top box is m•g where m = 6.0 kg. The force of gravity is 58.8

N. The upward force is not known but can be calculated if the Fnet = m•a equation is applied to the

free-body diagram. Since the acceleration is upward, the Fnet side of the equation would be equal to the force in the direction of

the acceleration (Fcontact) minus the force that opposes it (Fgrav). So

Fcontact - 58.8 N = (6.0 kg)•(2.0571 m/s2)

(Notice that the unrounded value of acceleration is used here; rounding will occur when the final answer is determined.) Solving

for Fcontact yields 71.14 N. This figure can be rounded to two significant digits - 71 N. So the dual combination of the system

analysis and the individual body analysis leads to an acceleration of 2.1 m/s2 and a contact force of 71 N.

Now the second problem-solving approach will be used to solve the same problem. In this solution, two individual object

analyses will be combined to generate a system of two equations capable of solving for the two unknowns. We will start this

analysis by presuming that we are solving the problem for the first time and do not know the acceleration nor the contact force.

The free-body diagrams for the individual objects are shown below.

Note that the Fgrav values for the two boxes have been included on the diagram. These were calculated using Fgrav = m•g where

m=6.0 kg for the top box and m=8.0 kg for the bottom box. The contact force (Fcontact) on the top box is upward since the

bottom box is pushing it upward as the system of two objects accelerates upward. The contact force (Fcontact) on the bottom box

is downward since the top box pushes downward on the bottom box as the acceleration occurs. These two contact forces are

equal to one another since they result from a mutual interaction between the two boxes. The third force on the bottom box is the

force of the scale pushing upward on it with 166 N of force; this value was given in the problem statement.

Applying Newton's second law to these two free-body diagrams leads to Equation 5 (for the 6.0-kg box) and Equation 6 (for the

8.0-kg box).

Fcontact - 58.8 = 6.0 • a

166 - Fcontact - 78.4 = 8.0 • a

Now that a system of two equations has been developed, algebra can be used to solve for the two unknowns.

Equation 5 can be used to write an expression for the contact force (Fcontact) in terms of the acceleration (a).

Fcontact = 6.0 • a + 58.8

This expression for Fcontact can then be substituted into equation 6. Equation 6 then becomes

166 - (6.0 • a + 58.8) - 78.4 = 8.0 • a

The following algebraic steps are performed on the above equation to solve for acceleration.

166 - 6.0 • a - 58.8 - 78.4 = 8.0 • a

166 - 58.8 - 78.4 = 8.0 • a + 6.0 • a

28.8 = 14.0 a

a = 2.0571 m/s2 = ~2.1 m/s2

Now the value for acceleration (a) can be substituted back into the expression for Fcontact (Fcontact = 6.0 • a + 58.8) to solve for

Fcontact. The contact force is 71.14 N (~71 N).

It should be noted that the second approach to this problem yields the same numerical answers as the first approach. Students

are encouraged to use the approach that they are most comfortable with.

For additional practice, consider the following two-body problems. A shortened version of the solution has been provided for each

problem. The topic of two-body problems will be returned to in the next chapter when we consider situations involving pulleys


4 of 5 9/18/2012 7:28 PM

and objects moving in different directions.


1. A truck hauls a car cross-country. The truck's mass is 4.00x103 kg and the car's mass is 1.60x103

kg. If the force of propulsion resulting from the truck's turning wheels is 2.50x104 N, then determine

the acceleration of the car (or the truck) and the force at which the truck pulls upon the car. Assume

negligible air resistance forces.

See Answer

2. A 7.00-kg box is attached to a 3.00-kg box by rope 1. The 7.00-kg box is pulled by rope 2

with a force of 25.0 N. Determine the acceleration of the boxes and the tension in rope 1. The

coefficient of friction between the ground and the boxes is 0.120.

See Answer

3. A tractor is being used to pull two large logs across a field. A chain connects the logs to each other; the front log is connected

to the tractor by a separate chain. The mass of the front log is 180 kg. The mass of the back log is 220 kg. The coefficient of

friction between the logs and the field is approximately 0.45. The tension in the chain connecting the tractor to the front log is

1850 N. Determine the tension in the chain that connects the two logs.

See Answer

4. Two boxes are held together by a strong wire and attached to the ceiling of an elevator by a second wire

(see diagram). The mass of the top box is 14.2 kg; the mass of the bottom box is 10.4 kg. The elevator

accelerates upwards at 2.84 m/s2. (Assume the wire is relatively massless.)

(a) Find the tension in the top wire (connecting points A and B).

(b) Find the tension in the bottom wire (connecting points C and D).

See Answer


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5 of 5 9/18/2012 7:28 PM

Physics Tutorial

1-D Kinematics

Newton's Laws



Momentum and Its

Conservation


Circular Motion and

Satellite Motion

Thermal Physics

Static Electricity

Current Electricity

Waves




of Light


of Light

Minds on Physics

The Calculator Pad

Multimedia Studios

Shockwave Studios

The Review Session

Physics Help

Curriculum Corner

The Laboratory

The Photo Gallery

ACT Test Center

Student Extras

Teacher's Guide



Newton's Third Law of Motion

Newton's Third Law | Identifying Action and Reaction Force Pairs

Newton's Third Law

A force is a push or a pull upon an object that results from its interaction with another object.

Forces result from interactions! As discussed in Lesson 2, some forces result from contact

interactions (normal, frictional, tensional, and applied forces are examples of contact forces) and other forces are the result of

action-at-a-distance interactions (gravitational, electrical, and magnetic forces). According to Newton, whenever objects A and B

interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the

chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair

and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of

motion. Formally stated, Newton's third law is:

For every action, there is an equal and opposite reaction.

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects.

The size of the forces on the first object equals the size of the force on the second object. The direction of the

force on the first object is opposite to the direction of the force on the second object. Forces always come in

pairs - equal and opposite action-reaction force pairs.

A variety of action-reaction force pairs are evident in nature. Consider the propulsion of a fish through the

water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the

water. Since forces result from mutual interactions, the water must also be pushing the fish forwards,

propelling the fish through the water. The size of the force on the water equals the size of the force on the fish;

the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). For every action,

there is an equal (in size) and opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim.

Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air

downwards. Since forces result from mutual interactions, the air must also be pushing the bird

upwards. The size of the force on the air equals the size of the force on the bird; the direction of the

force on the air (downwards) is opposite the direction of the force on the bird (upwards). For every

action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make

it possible for birds to fly.

Consider the motion of a car on the way to school. A car is equipped with wheels that spin. As the

wheels spin, they grip the road and push the road backwards. Since forces result from mutual

interactions, the road must also be pushing the wheels forward. The size of the force on the road

equals the size of the force on the wheels (or car); the direction of the force on the road (backwards) is opposite the direction of

the force on the wheels (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-

reaction force pairs make it possible for cars to move along a roadway surface.


1. While driving down the road, a firefly strikes the windshield of a bus and makes a quite

obvious mess in front of the face of the driver. This is a clear case of Newton's third law of

motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater:

the force on the firefly or the force on the bus?

See Answer

2. For years, space travel was believed to be impossible because there was nothing that rockets could push off of in space in

order to provide the propulsion necessary to accelerate. This inability of a rocket to provide propulsion is because ...

a. ... space is void of air so the rockets have nothing to push off of.

b. ... gravity is absent in space.

c. ... space is void of air and so there is no air resistance in space.

d. ... nonsense! Rockets do accelerate in space and have been able to do so for a long time.

See Answer

3. Many people are familiar with the fact that a rifle recoils when fired. This recoil is the result of action-


Newton's Third Law http://www.physicsclassroom.com/Class/newtlaws/u2l4a.cfm

1 of 2 9/18/2012 7:28 PM

reaction force pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to

push forward on the bullet. Consistent with Newton's third law of motion, the bullet pushes backwards

upon the rifle. The acceleration of the recoiling rifle is ...

a. greater than the acceleration of the bullet.

b. smaller than the acceleration of the bullet.

c. the same size as the acceleration of the bullet.

See Answer

4. In the top picture (below), Kent Budgett is pulling upon a rope that is attached to a wall. In the bottom picture, the Kent is

pulling upon a rope that is attached to an elephant. In each case, the force scale reads 500 Newton. Kent is pulling ...

a. with more force when the rope is attached to the wall.

b. with more force when the rope is attached to the elephant.

c. the same force in each case.

See Answer

Next Section: Identifying Action and Reaction Force Pairs

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Physics Tutorial

1-D Kinematics

Newton's Laws



Momentum and Its

Conservation


Circular Motion and

Satellite Motion

Thermal Physics

Static Electricity

Current Electricity

Waves




of Light


of Light

Minds on Physics

The Calculator Pad

Multimedia Studios

Shockwave Studios

The Review Session

Physics Help

Curriculum Corner

The Laboratory

The Photo Gallery

ACT Test Center

Student Extras

Teacher's Guide



Newton's Third Law of Motion

Newton's Third Law | Identifying Action and Reaction Force Pairs

Identifying Action and Reaction Force Pairs

According to Newton's third law, for every action force there is an equal (in size) and opposite

(in direction) reaction force. Forces always come in pairs - known as "action-reaction force

pairs." Identifying and describing action-reaction force pairs is a simple matter of identifying the two interacting objects and

making two statements describing who is pushing on whom and in what direction. For example, consider the interaction between

a baseball bat and a baseball.

The baseball forces the bat to the left; the bat forces the ball to the right. Together, these two forces exerted upon two different

objects form the action-reaction force pair. Note that in the description of the two forces, the nouns in the sentence describing

the forces simply switch places.

Consider the following three examples. One of the forces in the mutual interaction is described; describe the other force in the

action-reaction force pair. Click the button to view the answer.

Baseball pushes glove leftwards.

See Answer

Bowling ball pushes pin leftwards.

See Answer

Enclosed air particles push balloon wall outwards.

See Answer


1. Consider the interaction depicted below between foot A, ball B, and foot C. The three objects interact simultaneously (at the

same time). Identify the two pairs of action-reaction forces. Use the notation "foot A", "foot C", and "ball B" in your statements.

Click the button to view the answer.


Identifying Action and Reaction Force Pairs http://www.physicsclassroom.com/Class/newtlaws/u2l4b.cfm

1 of 2 9/18/2012 7:29 PM

See Answer

2. Identify at least six pairs of action-reaction force pairs in the following diagram.

See Answer

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Introduction

Chapter 1: Energy - What Is It?

Chapter 2: Electricity

Chapter 3: Static Electricity & Resistance

Chapter 4: Electrical Circuits

Chapter 5: Stored Energy & Batteries

Chapter 6: Generators, Turbines and Power

Plants

Chapter 7: Electricity Transmission System

Chapter 8: Fossil Fuels - Coal, Oil and

Natural Gas

Chapter 9: Natural Gas Distribution System

Chapter 10: Biomass Energy

Chapter 11: Geothermal Energy

Chapter 12: Hydro Power

Chapter 13: Nuclear Energy - Fission and

Fusion

Chapter 14: Ocean Energy

Chapter 15: Solar Energy

Chapter 16: Wind Energy

Chapter 17: Renewable vs. Nonrenewable -

Environment & Air Quality

Chapter 18: Energy for Transportation

Chapter 19: Saving Energy and Energy

Efficiency

Chapter 20: Hydrogen and Energy In Our

Future

Conclusion

Table of Content

Electricity figures everywhere in our lives. Electricity lights up our homes, cooks our

food, powers our computers, television sets, and other electronic devices. Electricity

from batteries keeps our cars running and makes our flashlights shine in the dark.

Here's something you can do to see the importance of electricity. Take a walk through

your school, house or apartment and write down all the different appliances, devices

and machines that use electricity. You'll be amazed at how many things we use each

and every day that depend on electricity.

But what is electricity? Where does it come from? How does it work? Before we

understand all that, we need to know a little bit about atoms and their structure.

All matter is made up of atoms, and atoms are made

up of smaller particles. The three main particles making

up an atom are the proton, the neutron and the

electron.





charge. Neutrons are neutral – they have neither a

positive nor a negative charge.

There are many different kinds of atoms, one for each

type of element. An atom is a single part that makes up

an element. There are 118 different known elements that make up every thing! Some

elements like oxygen we breathe are essential to life.




usually needs to be the same as the number of

protons. If the numbers are the same, the atom is

called balanced, and it is very stable.

So, if an atom had six protons, it should also have

six electrons. The element with six protons and six

electrons is called carbon. Carbon is found in

abundance in the sun, stars, comets, atmospheres

of most planets, and the food we eat. Coal is made

of carbon; so are diamonds.

Some kinds of atoms have loosely attached

electrons. An atom that loses electrons has more protons than electrons and is

positively charged. An atom that gains electrons has more negative particles and is

negatively charge. A "charged" atom is called an "ion."

Electrons can be made to move from one atom to another. When those electrons

move between the atoms, a current of electricity is created. The electrons move from

one atom to another in a "flow." One electron is attached and another electron is lost.

This chain is similar to the fire fighter's bucket brigades in olden times. But instead of

passing one bucket from the start of the line of people to the other end, each person

would have a bucket of water to pour from one bucket to another. The result was a

lot of spilled water and not enough water to douse the fire. It is a situation that's very

similar to electricity passing along a wire and a circuit. The charge is passed from



1 of 2 9/18/2012 7:16 PM

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Scientists and engineers have learned many ways to move electrons off of atoms.

That means that when you add up the electrons and protons, you would wind up

with one more proton instead of being balanced.

Since all atoms want to be balanced, the atom that has been "unbalanced" will look

for a free electron to fill the place of the missing one. We say that this unbalanced

atom has a "positive charge" (+) because it has too many protons.

Since it got kicked off, the free electron moves around waiting for an unbalanced

atom to give it a home. The free electron charge is negative, and has no proton to

balance it out, so we say that it has a "negative charge" (-).


Scientists and engineers have found several ways to create large numbers of positive

atoms and free negative electrons. Since positive atoms want negative electrons so

they can be balanced, they have a strong attraction for the electrons. The electrons

also want to be part of a balanced atom, so they have a strong attraction to the

positive atoms. So, the positive attracts the negative to balance out.

The more positive atoms or negative electrons you have, the stronger the attraction

for the other. Since we have both positive and negative charged groups attracted to

each other, we call the total attraction "charge."

Energy also can be measured in joules. Joules sounds exactly like the word jewels, as

in diamonds and emeralds. A thousand joules is equal to a British thermal unit.

When electrons move among the atoms of matter, a current of electricity is created.

This is what happens in a piece of wire. The electrons are passed from atom to atom,

creating an electrical current from one end to other, just like in the picture.

Electricity is conducted through some things better than others do. Its resistance

measures how well something conducts electricity. Some things hold their electrons

very tightly. Electrons do not move through them very well. These things are called

insulators. Rubber, plastic, cloth, glass and dry air are good insulators and have very

high resistance.

Other materials have some loosely held electrons, which move through them very

easily. These are called conductors. Most metals – like copper, aluminum or steel –

are good conductors.

Where Does the Word 'Electricity' Come From?

In the next chapter read about Static Electricity & Resistance.


2 of 2 9/18/2012 7:16 PM

Chapter 4a: Earth Science

Weathering and Erosion are two distinct processes that cause change on the surface of our planet. What are the differences between the two?

Read: Weathering and Erosion

Plate tectonics is the study of how large sections of the Earth's crust are constantly in motion causing different landforms to appear. Convergent Boundaries, Divergent Boundaries, and Transform Boundaries are three of the most common types.

Read: Plate Tectonics

Three of the most common soil types are clay, loam, and sand. Note the difference between the types.

Read: Soil Types

The Water Cycle is the continuous action of precipitation, condensation, and evaporation. Note in the reading the percentages of water in oceans.

Read: Water Cycle

What is the difference between weather and climate?

Read: Weather and Climate

Reading a weather map is a necessary skill if you live in the state of Florida. What do the symbols for cold front, warm front, high pressure system, and low pressure system look like?

Read: Weather Systems

http://www.nature.nps.gov/geology/usgsnps/misc/gweaero.html

http://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html

http://www.historyforkids.org/learn/environment/soiltypes.htm

http://ga.water.usgs.gov/edu/watercycle.html

http://www.rkdn.org/outdoors/weather.htm

http://www.weatherwizkids.com/weather-forecasting.htm

What’s the difference between weathering

and erosion?

Weathering involves two processes that often work in concert to

decompose rocks. Both processes occur in place. No movement is

involved in weathering. Chemical weathering involves a chemical

change in at least some of the minerals within a rock. Mechanical

weathering involves physically breaking rocks into fragments without

changing the chemical make-up of the minerals within it. It’s important

to keep in mind that weathering is a surface or near-surface process. As

you know, metamorphism also produces chemical changes in rocks,

but metamorphic chemical changes occur at depth where either the

temperature and/or pressure are significantly higher than conditions

found on the Earth’s surface.

As soon as a rock particle (loosened by one of the two weathering

processes) moves, we call it erosion or mass wasting. Mass wasting is

simply movement down slope due to gravity. Rock falls, slumps, and

debris flows are all examples of mass wasting. We call it erosion if the

rock particle is moved by some flowing agent such as air, water or ice.

So, here it is: if a particle is loosened, chemically or mechanically,

but stays put, call it weathering. Once the particle starts moving, call it

erosion.

| USGS Geology in the Parks home | NPS Park Geology Tour

home |

This site is a cooperative endeavor of the

US Geological Survey Western Earth Surface Processes Team

and the National Park Service.

Please share your comments and suggestions with us!

[email protected]

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This page was last updated on 11/22/99

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1 of 1 9/18/2012 7:31 PM

Skip Navigation

The theory of plate tectonics has done for geology whatCharles Darwin's theory of evolution did for biology. Itprovides geology with a comprehensive theory thatexplains "how the Earth works." The theory wasformulated in the 1960s and 1970s as new informationwas obtained about the nature of the ocean floor,Earth's ancient magnetism, the distribution of volcanoesand earthquakes, the flow of heat from Earth's interior,and the worldwide distribution of plant and animalfossils.

The theory states that Earth's outermost layer, thelithosphere, is broken into 7 large, rigid pieces calledplates: the African, North American, South American,Eurasian, Australian, Antarctic, and Pacific plates.Several minor plates also exist, including the Arabian,Nazca, and Philippines plates.

The plates are all moving in different directions and atdifferent speeds (from 2 cm to 10 cm per year--aboutthe speed at which your fingernails grow) in relationshipto each other. The plates are moving around like cars ina demolition derby, which means they sometimes crashtogether, pull apart, or sideswipe each other. The placewhere the two plates meet is called a plate boundary.

Plate Tectonics

Convergent

Boundaries

Divergent

Boundaries

Transform

Boundaries

Earth Floor: Plate Tectonics http://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html

1 of 2 9/18/2012 7:33 PM

Boundaries have different names depending on how thetwo plates are moving in relationship to each other

crashing: Convergent Boundaries,pulling apart: Divergent Boundaries,or sideswiping: Transform Boundaries

With respect to plate boundaries is your home locatedin the middle of, or near the boundary of a plate? Whatdoes this mean for you tectonically?

Next

Plate Tectonics | Convergent Boundaries |

Divergent Boundaries | Transform Boundaries

Diversity | Adaptation | Plate Tectonics |

Cycles | Spheres | Biomes | Geologic Time

Site maintained by the ETE Team

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2 of 2 9/18/2012 7:33 PM

Soil Types Triangle

Kidipede home > Geology > Soil Types

All dirt is basically made of three different kinds of

particles. These are clay, sand, and loam. Clay is very

fine, small inorganic particles, worn down from rock.

Sand is bigger, coarser particles, also from rock, often

quartz or silica. Loam is organic particles (bits of dead

plants). Geologists and archaeologists can describe

any particular soil by saying where it lies in this triangle:

The best soils for farming have a lot of loam in them; they fall near the top of

the triangle, like the blue spot. Down where the purple spot is, that would be

good clay for making pottery. Over by the green dot, that's sand that you can

melt down into glass. The orange dot marks a good soil with a lot of loam in

it, , but it does have a lot of clay in it, and that makes it heavy and hard to

plow.

You need animals to pull the plow. A lot of northern European soils are like

that, and also the soil in river valleys like the Nile. The yellow dot marks soils

that are more typically Mediterranean: a mixture of loam and sand, with only

a little clay, light enough to plow by hand.

To find out more about soil types in archaeology, check out this book from Amazon.com or from

your library:

Archaeology for Kids: Uncovering the Mysteries of Our Past, by Richard

Panchyk (2001). With twenty-five projects, like counting tree rings, and

Soil Types - Geology for Kids! http://www.historyforkids.org/learn/environment/soiltypes.htm

1 of 2 9/18/2012 7:33 PM

serializing cars from photographs. Includes a project on soil types.

Back to environment

History for Kids home page

Cite this page: Carr, Karen (PhD).

Kidipede - History for Kids. 2012.

http://www.historyforkids.org/learn/environment/soiltypes.htm

Soil Types - Geology for Kids! http://www.historyforkids.org/learn/environment/soiltypes.htm

2 of 2 9/18/2012 7:33 PM

The Water Cycle - Water Science for Schools

The Water Cycle

Earth's water is always in movement, and the natural water cycle, also known as the hydrologic cycle,

describes the continuous movement of water on, above, and below the surface of the Earth. Water is

always changing states between liquid, vapor, and ice, with these processes happening in the blink of an

eye and over millions of years.

Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater storage

Groundwater discharge · Groundwater storage · Ice and snow · Infiltration · Oceans

Precipitation · Runoff · Snowmelt · Springs · Streamflow · Sublimation

Global water distribution

For an estimated explanation of where Earth's water exists, look at the chart below. By now, you know that

the water cycle describes the movement of Earth's water, so realize that the chart and table below

represent the presence of Earth's water at a single point in time. If you check back in a thousand or million

years, no doubt these numbers will be different!

Notice how of the world's total water supply of about 332.5 million cubic miles of water, over 96 percent is

saline. And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of

freshwater is in the ground. Fresh surface-water sources, such as rivers and lakes, only constitute about

22,300 cubic miles (93,100 cubic kilometers), which is about 1/150th of one percent of total water. Yet,

rivers and lakes are the sources of most of the water people use everyday.

The water cycle, U.S. Geological Survey (USGS) Water Science School http://ga.water.usgs.gov/edu/watercycle.html

1 of 3 9/18/2012 7:35 PM

Source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), 1993, Water in Crisis: A

Guide to the World's Fresh Water Resources (Oxford University Press, New York).

Where is Earth's water?

For a detailed explanation of where Earth's water is, look at the data table below. Notice how of the world's

total water supply of about 333 million cubic miles (1,386 million cubic kilometers) of water, over 96

percent is saline. And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30

percent of freshwater is in the ground. Thus, rivers and lakes that supply surface water for human uses

only constitute about 22,300 cubic miles (93,100 cubic kilometers), which is about 0.007 percent of total

water, yet rivers are the source of most of the water people use.

One Estimate of Global Water Distribution

(Numbers are rounded)

Water source Water volume, incubic miles

Water volume, incubic kilometers

Percent offreshwater

Percentoftotalwater

Oceans, Seas, &

Bays

321,000,000 1,338,000,000 -- 96.5

Ice caps, Glaciers,

& Permanent

Snow

5,773,000 24,064,000 68.6 1.74

Groundwater 5,614,000 23,400,000 -- 1.7

Fresh 2,526,000 10,530,000 30.1 0.76

Saline 3,088,000 12,870,000 -- 0.93

Soil Moisture 3,959 16,500 0.05 0.001


2 of 3 9/18/2012 7:35 PM

Water source Water volume, incubic miles

Water volume, incubic kilometers

Percent offreshwater

Percent oftotalwater

Ground Ice &

Permafrost

71,970 300,000 0.86 0.022

Lakes 42,320 176,400 -- 0.013

Fresh 21,830 91,000 0.26 0.007

Saline 20,490 85,400 -- 0.007

Atmosphere 3,095 12,900 0.04 0.001

Swamp Water 2,752 11,470 0.03 0.0008

Rivers 509 2,120 0.006 0.0002

Biological Water 269 1,120 0.003 0.0001

Source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor),

1993, Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press,

New York).

U.S. Department of the Interior | U.S. Geological SurveyURL: http://ga.water.usgs.gov/edu/watercycle.htmlPage Contact Information: Howard PerlmanPage Last Modified: Thursday, 13-Sep-2012 07:10:59 EDT


3 of 3 9/18/2012 7:35 PM

Layers of the atmosphere

From "Ultimate Visual Dictionary of

Science," Stoddart 1998.

Earth's wind patterns

From "Ultimate Visual Dictionary of

Science," Stoddart 1998.

Measuring and Monitoring Weather

Climate | Weather Watching | Avalanches | The Sun

Clouds and Precipitation | Wind

A. Weather and Climate

Where is weather created?

Weather is created and changed by the atmosphere, specifically the

troposphere, which is in continuous motion.

The troposphere is the layer of the atmosphere that is closest to Earth. It is

approximately 10 kilometers in depth, where it meets the stratosphere.

Each layer is identified according to its variations in temperature compared to

height. For example, in the troposphere, the temperature decreases with height,

and in the stratosphere the temperature increases with height.

The whole atmosphere, from the troposphere to the exosphere, is only 700

kilometers deep.

This mixture of colorless, tasteless, odorless gases is the only thing that makes

the earth an excellent environment for life. Without it, we could not live here any

more than we could on Mars or the Moon. The atmosphere is the source of the

air we breathe, the warmth we feel, the protection we have from the sun's harmful

radiation, the water we drink and our protection from meteorites.

How is weather created?

The heat of the sun is not equal between the

North and South poles and the Equator.

It is more intense at the equator and

gradually less so towards each of the poles,

where it is coldest.

The difference in the temperatures in the

various regions between the equator and

each of the poles means that the air is

warmer and colder to varying degrees

around the Earth. Since warm air rises and

cold air sinks, there are differences in air

pressure in the troposphere, which causes

continuous motion of the air. The movement

of the air causes the constantly changing

weather patterns on the Earth.

The constantly moving air is actually the source of winds around the world. Hot air rises at the equator and falls at the

poles where it is the coldest (receiving less of the sun's warmth). There are three different zones of circulating air

between the equator and each pole. Within each of these zones, the air cycles as it is cooled and warmed.

The places where these zones meet have some of the most turbulent weather. Except at the equator, powerful jet

streams are created where these cycling masses of air come together and separate as they continue their cycle from

lower to higher parts of the troposphere.

Where the air is sinking (colder air), there is high pressure. Where the air is rising (warmer air), there is low-pressure.

High-pressure weather tends to be clear and low-pressure weather tends to be cloudy, wet, and changeable.

Meteorologists' knowledge of these systems, along with daily monitoring of local effects, allows them to predict

weather. Air currents drive the weather globally, but there are other influences on the weather including the moisture

content of the air.

Measuring and monitoring weather Climate http://www.rkdn.org/outdoors/weather.htm

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Web Links

Environment Canada

Weather @ cbc.ca

Weather Gone Wild

The Weather Channel

The Weather Underground, Inc

UK Weather

How much moisture air contains is a function of how close the air is to a body of water. This drives the formation of

clouds and the resulting precipitation.

Other geographical features that influence local weather variations include nearby mountains. Mountains can influence

weather such as fog, Chinook winds and rain. Although these can be related to and do influence global weather

patterns, a mountain's immediate weather influence doesn't necessarily apply to a large area.

What is the difference between weather and climate?

Weather - is generally noted on a day to day basis, with attention to particular daily changes in the patterns that bring

rain, high winds, cold temperatures, etc. locally. Predictions are generally made for a day, two days or up to a week in

advance. This is the information that helps us make our daily decisions about traveling and how to dress for the

weather.

Climate - is the overall weather over time. It gives information about typical seasonal patterns, or patterns generally

found in a large geographical area. We use this information to generalize and describe weather in a province, a state

or a country over time. For example, people in the southern United States might generally assume that Canadians,

especially those that live in Northern Canada, have very cold weather in general (which is true, in some areas

especially), without taking into consideration that some summer daily temperatures can be quite warm, even

comparable to some states. The climate is the average temperature, average rainfall, and so on.

Why do we measure weather and monitor climate?

Weather conditions are usually measured and described in terms of temperature, wind speed and direction, cloud

cover, and precipitation (precipitation includes rain, snow, hail and any other form that falls from clouds).

We measure weather because we are interested in knowing what the daily temperature is, and whether that

temperature is normal according to the history of the climate for that area. We measure weather so that people can

make daily clothing decisions, as well as plans about local and international travel. Weather and climate information is

very important to those people who are planning vacations.

Generally people don't want to visit tropical areas during the rainy season, nor do some people want to visit Canada in

the height of winter. There is no way to know what specific temperature and precipitation you will receive for the

specific days of your vacation, but you can choose dates that, according to climate information, are more likely to have

warm weather and less likely to have an abundance of rain.

We measure weather and monitor climate (weather over time) for even more

important reasons, including the safety of people. Based on weather monitoring and

recording conditions that lead up to a hurricane or tornado and other potentially

disastrous weather, we are able to predict when an area might be hit with such

phenomena. The further ahead we know about these conditions, the more time

people have to prepare their homes and property or even evacuate.

By monitoring weather over time, we have also been able to learn about the effect

that we, as humans have been having on our environment and we are learning about

ways that we can make changes that are better for the environment. For example,

the Greenhouse Effect is being monitored by measuring temperature and using

climate data to compare temperature changes from historical to present time,

especially since the industrial revolution.

Atmospheric scientists and meteorologists measure, record and communicate

weather patterns via weather maps, which are now usually electronically generated

with computer technology in many formats. The ones used by meteorologists on your local news are simplified and

interpreted by the news staff so that everyone can get the information they need from the report without knowing a

whole lot about weather.

To see more sophisticated examples, go to the weather website of your local news or government weather station and

watch the weather news, especially the Weather Channel (in Canada).

On detailed weather maps lines, called isobars, show the areas where air pressure (barometric pressure) is equal.


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Weather map

From "Ultimate Visual Dictionary of Science,"

Stoddart 1998.

Lines with bumps and/or spike-type symbols indicate where the air

masses meet, which indicates where storms are occurring.

The bumps represent warm fronts and the spikes (or triangles)

represent cold fronts.

One of the other major symbols shows wind direction as reported from

various weather stations. These weather stations are indicated by a

dot.

A 'key' shape joined to the dot indicates the wind direction. The

direction of the key is the direction from which the wind is blowing.

Climate | Weather Watching | Avalanches | The Sun

Clouds and Percipitation | Wind


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Weather Forecasting

How do meteorologists forecast the weather?Weather forecasting is a prediction of what the weather will be like in an

hour, tomorrow, or next week. Weather forecasting involves a combination ofcomputer models, observations, and a knowledge of trends and patterns. Byusing these methods, reasonable accurate forecasts can be made up to seven

days in advance.

What are weather station symbols?Weather symbols are used on my weather maps as shorthand for the

conditions at weather observing stations.

Click Here to see a complete list of all the weather station symbols.

Click Here for an easy print out of the different weather station symbols.

What is a High Pressure System?A high pressure system is a whirling mass of cool, dry air that generally

brings fair weather and light winds. When viewed from above, winds spiral outof a high-pressure center in a clockwise rotation in the Northern Hemisphere.These bring sunny skies. A high pressure system is represented as a big, blue

H.

HWhat is a Low Pressure System?

A low pressure system is a whirling mass of warm, moist air that generallybrings stormy weather with strong winds. When viewed from above, windsspiral into a low-pressure center in a counterclockwise rotation in the

Northern Hemisphere. A low pressure system is represented as a big, red L.

Weather Wiz Kids weather information for kids http://www.weatherwizkids.com/weather-forecasting.htm

1 of 5 9/18/2012 7:36 PM

LWhat is an air mass?

An air mass is an extremely large body of air whose properties oftemperature and moisture content (humidity), at any given altitude, are fairlysimilar in any horizontal direction. Air masses can cover large (hundreds ofmiles) areas. Air masses can control the weather for a relatively long time

period: from a period of days, to months. Most weather occurs along theperiphery of these air masses at boundaries called fronts. There are 4

general air mass classifications categorized according to the source region:polar, tropical, continental and marine.

1.) Polar latitudes (P) - located poleward of 60 degrees north and south

2.) Tropical latitudes (T) - located within about 25 degrees of the equator

3.) Continental (c) - located over large land masses, dry

4.) Marine (m) - located over the oceans

We can then make combinations of the above to describe various types of airmasses.

cP continental polar cold, dry, stable

cT continental tropical hot, dry, stable air aloft, unstable surface air

mP maritime polar cool, moist, and unstable

mT maritime tropical warm, moist, usually unstable

What type of air masses affect the United States?There are many types of air masses that can affect the U.S., since it is such a

large country. Below are a few examples:

cP - wintertime bitter cold can extent to Southern U.S. and even Florida

causing crop damage. Require long, clear nights, which means strong

radiational cooling of air near the surface. A stable air mass. Little moistureadded so air is dry

mP - Winter cP air moves over a region such as the NE Pacific, picking up

some warmth and moisture from the warmer ocean. In the case of the PacificNW mountains force the air to rise (orographic lifting) causing rain.

mT - wintertime source for the SW U.S. is the subtropical East Pacific

Ocean. mT air that influences weather east of the Rocky Mountains comesfrom the Gulf of Mexico, but only influences winter weather in the SEstates. Occasionally, slow moving weather systems in SW flow aloft candraw up moisture at mid and low levels producing precipitation.

cT - Continental tropical air usually only influences the U.S. in summertime as

warm, dry air is pumped up off of the Mexican Plateau. It is usually fairly

stable and dry, and if it becomes stagnant over the midwest, results in adrought. Deaths associated with the 1995 heat wave in the midwest were theresult of cT and mT air which stagnated over the central and eastern part ofthe U.S.

What is a front?A front is a boundary between two different air masses, resulting in stormy

weather. A front usually is a line of separation between warm and cold airmasses.


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How do you identify a front on a surface weather map or by

your own weather observations?Look for: Sharp temperature changes over a relatively short distance, changein moisture content, rapid shifts in wind direction, pressure changes, clouds

and precipitation patterns.

What is a cold front?A cold front is a boundary between two air masses, one cold and the other

warm, moving so that the colder air replaces the warmer air. A cold front isrepresented as a blue line with the teeth pointing toward the direction on

movement.

What is a warm front?A warm front is a boundary between two air masses, one cool and the otherwarm, moving so that the warmer air replaces the cooler air. A warm front isrepresented as a red line with half circles pointing toward the direction on

movement.

What is a stationary front?A stationary front is a boundary between two air masses that more or lessdoesn’t move, but some stationary fronts can wobble back and forth forseveral hundred miles a day. A stationary front is represented as an

alternating warm and cold front symbol.

What is a occluded front?An occluded front is a combination of two fronts that form when a cold frontcatches up and overtakes a warm front. An occluded front is represented as a

purple line with teeth and half circles.

What is a trough?A trough on a weather map is an elongated area of relatively low pressure.

Troughs bring cloudy and rainy weather. A trough is represented by a hashmark line.


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What is a weather satellite?A weather satellite is a type of satellite that is primarily used to monitor theweather and climate of the Earth. Satellites can be either polar orbiting,seeing the same swath of the Earth every 12 hours, or geostationary,

hovering over the same spot on Earth by orbiting over the equator whilemoving at the speed of the Earth's rotation. These meteorological satellites

see more than clouds and cloud systems. City lights, fires, effects ofpollution, auroras, sand and dust storms, snow cover, ice mapping, boundariesof ocean currents, energy flows, etc., are other types of environmental

information collected using weather satellites.

What is radar?Radar is an electronic instrument, which determines the direction and

distance of objects that reflect radio energy back to the radar site. It standsfor Radio Detection and Ranging. This is what meteorologists use to see rain

or snow.

What is Doppler Radar?Doppler Radar detects precipitation intensity, wind direction and speed, andprovides estimates of hail size and rainfall amounts. Doppler Radar gives

forecasters the capability of providing early detection of severe

thunderstorms that may bring strong damaging winds, large hail, heavy rain,and possibly tornadoes. Combined with satellites, radar gives forecasters theultimate tools to provide accurate forecasts and advanced severe weather

warnings.

How does Doppler Radar work?Doppler Radar gets its name from the Doppler Effect. Have you ever listenedto a train whistle as it was coming toward you? You probably noticed that thepitch of the whistle changed as the train passed you and moved away. Thischange in the frequency of sound is called the Doppler Effect. Doppler Radar

measures the changes in the frequency of the signal it receives to determinethe wind.

What is NEXRAD Radar?


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The National Weather Service has installed a new type of Doppler Radarcalled NEXRAD Radar. NEXRAD stands for Next Generation Radar. This radarproduces many different views of storms and rain that allows meteorologists

to determine if a storm could be severe.

Weather Forecasting Activities

Lesson Plan: Here is a great lesson plan on learning how to forecast. In thisactivity, kids learn about different forecasting tricks.

Lesson Plan: Here is a great lesson plan on weather symbols. This lessonplan will teach kids about the different types of weather symbols and showthem how they are used on a weather map. This is a PDF file, so you need to

have Adobe Acrobat Reader.

Lesson Plan: Here is a great lesson plan on weather symbols for youngerkids. This lesson plan requires kids to match the weather symbols to words.

You will need to download this file to then be able to print off copies for yourstudents.

The Doppler Effect Experiment: Here is a an experiment that teacheskids what the Doppler Effect is. They can learn how the Doppler Effectworks and why Doppler Radar is such an important tool in weather

forecasting.

Science Fair Project Ideas: Here is a complete list of science fairproject ideas. Discover the science behind the weather that impacts us every

day.

Home | About Crystal | Contact Crystal | Privacy Policy | ©Copyright 2010 Weather Wiz Kids®Weather Wiz Kids Store | Hurricanes | Tornadoes | Winter Storms | Clouds | Rain & Floods | Thunderstorms

Lightning | Wind | Temperature | Wildfires | Earthquakes | Volcanoes | Climate | Optical Illusions

Weather Experiments | Weather Safety | Weather Games | Weather Flashcards | Weather Jokes | Weather FolkloreWeather Words | Weather Instruments | Weather Photos | Career Corner | Weather Links


5 of 5 9/18/2012 7:36 PM

Chapter 4b: Space Science

Our solar systems is made up of many different types of of objects. These include sun, planets, asteroids, and comets. What is the difference between meteors and meteorites?

Read: Solar System

The moon goes through several phases while it revolves around the Earth. Note that the same side always faces the Earth, but at the same time except during a lunar eclipse, 50% of the moon is always lit by the sun (we just can't always see it). What is the difference between gibbous and crescent? What is the difference between waxing and waning? At what position is the moon in relation to to the Earth and Sun in its new, full, and quarter phases?

Read: Phases of the Moon

The moon has a profound affect on the Earth's tides. What affect does the position of moon have on regular tides? When do the Neap Tides and Spring Tides happen with relation to the Earth and the Sun. What is the difference between the apogee and the perigee?

Read: Moon - Tides

The word eclipse means to block. What is the difference between a solar ellipse and a lunar eclipse in relation to the positions of the Earth, Moon, and Sun? why aren't there solar and lunar eclipses every month.

Read: Eclipses

Read: Additional Space Science Facts

http://www.windows2universe.org/our_solar_system/solar_system.html

http://www.moonconnection.com/moon_phases.phtml

http://www.moonconnection.com/tides.phtml

http://eclipsegeeks.com/SolarandLunarEclipseDiagrams.aspx

https://angel.spcollege.edu/Permalink/Permalink.aspx?permalinkId=894a6af8-50ac-4436-ae0b-e856af93d1fa&permalinkType=0

Brought to you by the National Earth Science Teachers Association

Our Solar System

Our solar system is filled with a wide assortment of celestial bodies - the Sun itself, our eight

planets, dwarf planets, and asteroids - and on Earth, life itself! The inner solar system is

occasionally visited by comets that loop in from the outer reaches of the solar system on highly

elliptical orbits. In the outer reaches of the solar system, we find the Kuiper Belt and the Oort cloud.

Still farther out, we eventually reach the limits of the heliosphere, where the outer reaches of the

solar system interact with interstellar space. Solar system formation began billions of years ago,

when gases and dust began to come together to form the Sun, planets, and other bodies of the solar

system.

Comets are lumps of ice and dust that periodically come into the center of the solar system from its outer reaches.

Some comets make repeated trips to the inner solar system. When comets get close enough to the Sun, heat makes

them start to evaporate. Jets of gas and dust form long tails that we can see from Earth. This photograph shows Comet

Kohoutek, which visited the inner solar system in 1973. It has an orbit of about 75,000 years!

Image courtesy of NASA

The Solar System: The Sun, Planets, Dwarf Planets, Moons, Asteroids, C... http://www.windows2universe.org/our_solar_system/solar_system.html

1 of 5 9/18/2012 7:43 PM

Windows to the Universe Community

News Opportunities

Upcoming W2U Events Join Today - Benefits,

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Explore Our Solar System

Solar System Formation

Solar system formation began billions of years ago, when gases and dust began to come together

...Read more


2 of 5 9/18/2012 7:43 PM

Sun

The Sun is the closest star to Earth and is the center of our solar system. A giant, spinning ...Read

more

Planets

By the current count of astronomers, our solar system includes 8 planets and 5 dwarf planets.

...Read more

Dwarf Planets

In 2006 the International Astronomical Union (IAU) approved a new classification scheme for

...Read more

Asteroids

Asteroids are small bodies that are believed to be left over from the beginning of the solar ...Read

more

Meteors, Meteoroids, and Meteorites

Meteors are streaks of light, usually lasting just a few seconds, which people occasionally ...Read

more

Comets

Not long ago, many people thought that comets were a sign that something bad was about to ...Read

more


3 of 5 9/18/2012 7:43 PM

Poles in Space

The areas around the North and South Poles of planets, moons, and even the Sun are often

interesting ...Read more

Culture, Myth, and Arts

Make important cultural connections about the Sun, planets, and the Moon. ...Read more

Solar System Discoveries

Who discovered the planets? For many of the planets in the solar system, we'll never know! ...Read

more

More about Our Solar System

Kuiper Belt

Solar System Facts

Solar System News

Multimedia

Tours

Did you know?

Do you want to build your own custom comet?

Did you know that comets have two tails, not one?

Earth and Space Science Concept of the Day

Do you know what this word or phrase means?

Salinity

Click on the word to find out!

Research Highlights

Geologists Uncover Major Ancient Human Ancestor in South Africa

Scientists have discovered two fossil skeletons of an ancient human ancestor – a species related to


4 of 5 9/18/2012 7:43 PM

humans that had never been found before. The fossils, a young male and an adult female, formed

almost...Read more


5 of 5 9/18/2012 7:43 PM

Neptune's atmosphere shows a striped pattern of clouds. This cloud pattern is very similar to that

of Jupiter and Saturn. Neptune even has a Great Dark Spot similar to Jupiter's Great Red Spot.

The Great Dark Spot of Neptune is thought to be a hole, similar to the hole in the ozone layer on

Earth, in the methane cloud deck of Neptune.


This dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1

on Feb. 25, 1979, when the spacecraft was 5.7 million miles (9.2 million kilometers) from

Jupiter. Cloud details as small as 100 miles (160 kilometers) across can be seen here. The

colorful, wavy cloud pattern to the left of the Red Spot is a region of extraordinarily complex end

variable wave motion.


Lutetia is a medium-sized asteroid. It orbits the Sun in the main asteroid belt between the planets

Mars and Jupiter. This lumpy object is about 96 km (60 miles) in diameter. It isn't a perfect

sphere, though. Lutetia is 132 km (82 miles) across one way, but only about 76 km (47 miles)

long in another direction. The European space probe Rosetta flew past Lutetia in July 2010, and

gave us our first good look at the asteroid.

Image courtesy of ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA.

Have you ever seen the Southern or Northern Lights? Earth isn't the only planet that puts on

these beautiful light shows, which are also called the "aurora". Aurora have been seen at both

poles of Saturn, too, as well as at the poles of Jupiter. These "curtains of light" sometimes rise

1,200 miles (2,000 km) above the cloud tops near Saturn's poles. The Hubble Space Telescope

took this picture in 2004.

Image courtesy of NASA, ESA, J. Clarke (Boston University), and Z. Levay (STScI)

This historic image is the first ever taken from a spacecraft in orbit about Mercury, the innermost

planet of the solar system. Taken on 3/29/2011 by MESSENGER, it shows numerous craters

across the surface of the planet. Temperatures there can reach over 800°F because Mercury is so

close to the Sun and rotates so slowly. MESSENGER entered orbit around Mercury earlier in

March 2011.

NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of

This is an image of the solar system.

Click on image for full size

Related links:

News from NSF: A Newly Discovered Solar System Contains Scaled-Down Versions of Saturn

and Jupiter (2/14/08)

Podcasts from NSF: Systemic Search

Science books available along these topics...

The Solar System

The solar system is made up of the Sun, the 8 planets and 5 dwarf planets and their 174 known

moons, asteroids, comets, dust and gas. The planets, asteroids, and comets travel around the Sun,

the center of our solar system.

Most of the bodies in the solar system travel around the Sun along nearly circular paths or orbits,

and all the planets travel about the Sun in the anticlockwise direction (when viewed from above).

Solar system formation began billions of years ago, when gases and dust began to come together

to form the Sun, planets, and other bodies of the solar system.

Last modified July 15, 2010 by Randy Russell.

The Sun

The Sun is the closest star to Earth and is the center of our solar system. A giant, spinning ball of

very hot gas, the Sun is fueled by nuclear fusion reactions. The light from the Sun heats our

planet and makes life possible. The Sun is also an active star that displays sunspots, solar flares,

erupting prominences, and coronal mass ejections. These phenomena, which are all related to the

Sun's magnetic field, impact our near-Earth space environment and determine our "space

weather". In about five billion years, the Sun will evolve into a Red Giant, and eventually, a

White Dwarf star. Many cultures have had interesting myths about the Sun, in recognition of its

importance to life on Earth.

Planets

By the current count of astronomers, our solar system includes 8 planets and 5 dwarf planets.

The planets were formed during the process of solar system formation, when clumps began to

form in the disk of gas and dusk rotating about our young Sun. Eventually, only the planets and

other small bodies in the solar system remained. The four rocky planets at the center of the solar

system Mercury, Venus, Earth, Mars, are known as the inner planets. Jupiter, Saturn, Uranus,

and Neptune are all composed primarily of gas and are known as the outer planets. Find out more

about the planets through the links below.

This picture shows the sizes of the original three dwarf planets (Pluto, Ceres, and Eris) as

compared to Earth. It also shows Pluto's large moon Charon (and its two small moons Nix and

Hydra) and Eris's moon Dysnomia to scale. None of the distances between objects in this image

are to scale.


Images courtesy of NASA, ESA, JPL, and A. Feild (STScI).

Related links:

Ceres

Pluto

Haumea

Makemake

Eris

What is a planet?

Sizes of Earth, Luna, and the First Five Dwarf Planets

The Poles of the Dwarf Planets

Dwarf Planets

In 2006 the International Astronomical Union (IAU) approved a new classification scheme for

planets and smaller objects in our Solar System. Their scheme includes three classes of objects:

"small solar system bodies" (including most asteroids and comets), the much larger planets

(including Earth, Jupiter, and so on), and the new category of in-between sized "dwarf planets".

There are currently five official dwarf planets. Pluto, formerly the smallest of the nine

"traditional" planets, was demoted to dwarf planet status. Ceres, the largest asteroid in the main

asteroid belt between Mars and Jupiter, was also declared a dwarf planet. The three other (for

now!) dwarf planets are Eris, Makemake, and Haumea. Pluto, Makemake, and Haumea orbit the

Sun on the frozen fringes of our Solar System in the Kuiper Belt. Eris, also a Trans-Neptunian

Object, is even further from the Sun.

What's the difference between regular planets and dwarf planets? As you might guess, it's partly

an issue of size, with dwarf planets being smaller. But just how big does a planet need to be to

become a full-fledged planet instead of a dwarf? You might think the minimum size requirement

is arbitrary, but the size cutoff is actually based on other properties of the object and its history in

the Solar System.

Both planets and dwarf planets orbit the Sun, not other planets (in which case we call them

moons). Both must be large enough that their own gravity pulls them into the shapes of spheres;

this rules out numerous smaller bodies like most asteroids, many of which have irregular shapes.

Planets clear smaller objects out of their orbits by sucking the small bodies into themselves or

flinging them out of orbit. Dwarf planets, with their weaker gravities, are unable to clear out

their orbits.

Though there are just five dwarf planets now, their number is expected to grow. Scientists

estimate there may be 70 dwarf planets amongst outer solar system objects that have been

discovered already. Since we don't know the actual sizes or shapes of many of the objects we've

found (because they are so far away), we can't yet determine whether they are actually dwarf

planets or not. More observations and better telescopes will help us determine which other

objects are dwarf planets. Astronomers speculate that there may be 200 or so dwarf planets out

through the distance of the Kuiper Belt, an icy band of frozen planetoids on the edge of our Solar

System.

Asteroids

Asteroids are small bodies that are believed to be left over from the beginning of the solar system

4.6 billion years ago. They are rocky objects with round or irregular shapes up to several hundred

km across, but most are much smaller.

More than 100,000 asteroids lie in a belt between Mars and Jupiter. These asteroids lie in a

location in the solar system where there seems to be a jump in the spacing between the planets.

Scientists think that this debris may be the remains of an early planet, which broke up early in

the solar system. Several thousand of the largest asteroids in this belt have been given names.

The chances of an asteroid colliding with Earth are very small! But some do come close to Earth,

like Hermes (closest approach of 777,000 km).

This bright meteor, seen lighting up some clouds, was part of the Leonid Meteor Shower in

November 1998.


Courtesy of Lorenzo Lovato of Imola, Italy

Related links:

Meteor Showers

Geologists Discover New Way of Estimating Size and Frequency of Meteorite Impacts

Meteors

Meteors are streaks of light, usually lasting just a few seconds, which people occasionally see in

the night sky. They are sometimes called "shooting stars" or "falling stars", though they are not

stars at all. Meteors are caused by the entry of small pieces of rock, dust, or metal from space

into the atmosphere at extremely high speeds. These particles, called "meteoroids" when they are

floating around in space (think of very small asteroids), are traveling at incredible speeds of tens

of kilometers per second (tens of thousands of miles per hour) when they streak into the

atmosphere. The incredible pressure meteoroids experience when they collide with Earth's

atmosphere shatters them, transferring energy to atoms and molecules in the atmosphere, which

then release the energy by glowing. This glow produces the bright trails of light in the sky we see

as meteors.

Most meteoroid particles are quite small, ranging in size from a grain of sand to a pea-sized

pebble. Almost all of them disintegrate in the atmosphere long before reaching the ground. Very

rarely, a larger meteoroid actually survives to strike the ground, creating a meteor crater in a

huge explosion. This explosion often vaporizes whatever solid material is left of the meteoroid

after its fiery flight through the atmosphere. Sometimes, however, pieces of the meteoroid

survive and are found in the crater or nearby. These chunks of rock or metal are called

meteorites.

Meteors are not the same thing as comets. Meteors appear briefly as they streak through the sky.

Comets are much larger objects that are actually still out in space. Comets can form tails, and

though they do change position from night to night, they don't move fast enough for the eye to

notice; they seem to hang in place in the sky. There is a connection, though, between some

comets and some meteors. Several times each year Earth passes across the orbit of a comet,

where dust and small bits of rock from the comet have been left behind. When this happens we

can see many meteors in a single night; sometimes as many as 100 or more per hour! These

events are called meteor showers.

Especially bright meteors are called fireballs. Some fireballs are so bright that they can be seen

in the daytime. It would be possible to see meteors above any planet that has an atmosphere. A

camera on the Mars Exploration Rover Spirit captured a picture of meteor in the sky above Mars

in 2004!

How can you remember whether something is a meteor, a meteoroid, or a meteorite? Here's

how I do it! When they are out in space, like asteroids, they are called meteoroids. When they

are streaking through the atmosphere as bright flashes of light, we call them meteors - which

reminds me of meteorology, which is the science concerned with weather and the atmosphere.

[Meteorology is not the science of meteors!] When they reach the ground, we call them

meteorites - which reminds me of the stalactites and stalagmites that are found under the ground

in caves. I hope that helps you remember too!

Comets

Not long ago, many people thought that comets were a sign that something bad was about to

happen to them. People didn't understand how objects in the sky moved, so the sight of a comet

must have been very disturbing. There are many historical records and works of art which record

the appearance of comets and link them with terrible events such as wars or plagues.

Now we know that comets are lumps of ice and dust that periodically come into the center of the

solar system from somewhere in its outer reaches, and that some comets make repeated trips.

When comets get close enough to the Sun, heat makes them start to evaporate. Jets of gas and

dust form long tails that we can see from Earth. These tails can sometimes be millions of miles

long.

In 1985-1986, a spacecraft called Giotto visited the most famous comet, Halley, on Halley's most

recent visit to the inner solar system. In 1994, comet Shoemaker-Levy became trapped by the

gravity of Jupiter and plunged into Jupiter's atmosphere!

In 1996 and 1997 we saw comet Hyakutake, and comet Hale-Bopp. Hale-Bopp was one of the

brightest comets ever seen from Earth. Comet Linear was discovered in 1999 and made its

closest approach of the Sun in July 2000. The Stardust spacecraft flew by Comet Wild 2 in

January 2004, collecting samples of the comet to return to Earth. The newest comet mission is

Rosetta -- it will land on a comet named Churyumov-Gerasimenko!

Now scientists have identified a class of comets known as small comets (though they originally

were just called snowballs from space!)

Would you like build your own custom comet? If you would, check out our interactive comet

animation!

Poles in Space

The areas around the North and South Poles of planets, moons, and even the Sun are often

interesting and unusual places. We have discovered all sorts of unique behavior at these

locations, while on some planets, the characteristics of the poles are similar to those of Earth. On

some planets and moons, we still don't have observations from their poles so can only make

educated guesses of what we expect to find there based on our scientific understanding of the

celestial body. The links below provide an overview of what we know about the polar regions of

many of the major bodies in the solar system. An important concept related to the poles of the

planets is the amount of tilt of a planet's rotational axis relative to the plane of the ecliptic - the

orbital plane in which the planets orbit the Sun. Planets with a large tilt have stronger seasonal

behavior than planets without a tilt.

Solar System Discoveries

Who discovered the planets? For many of the planets in the solar system, we'll never know!

Some planets are so bright in the sky that the first observers of these planets are lost in the distant

past of early civilizations. Venus was carefully observed in early Mesoamerican cultures. The

most distant planets were discovered in the last century, and we're now still discovering Dwarf

planets, in our solar system and beyond. Visit the links here to find out more about what we

know about the discovery of planets."

Explore Solar System Discoveries

Discovery of Mercury

Mercury's orbit is so close to the Sun that it is difficult to see from the ground. This explains

...Read more

Discovery of Venus

Venus is one of the brightest objects in the sky, so it is clearly visible to the naked eye. ...Read

more

Discovery of Mars

Mars is much like Venus-- it's very bright and therefore easily spotted in the night sky. ...Read

more

Discovery of Jupiter

Jupiter is the largest planet in our solar system. It is also one of the brighter objects ...Read more

Discovery of Saturn

Like the inner planets and Jupiter, Saturn is clearly visible in the night sky. The ancient ...Read

more

Discovery of Uranus

Astronomer William Herschel is credited with the discovery of Uranus in 1781. He was using

...Read more

Discovery of Neptune

If you had a quiz question in school that asked what year Neptune was discovered, you'd

probably ...Read more

Discovery of Pluto

After the discovery of Neptune in 1846, mathematics suggested that there still might be a ...Read

more

Discovery of Ceres

Ceres is the largest asteroid in the main asteroid belt. It was classified as a "dwarf ...Read more

Discovery of Haumea

Haumea is a dwarf planet in our Solar System. Haumea is officially the fifth dwarf planet.

...Read more

Tools

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Current Moon Phase

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Apollo Missions

Apollo 13

Apollo 11

Moon Landing Hoax

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Understanding The Moon Phases

Have you ever wondered what causes the moon phases? We all know that its appearance changes

over time. But why? The good way to understand the phases of the moon is to examine an earth-

moon-sun diagram:

©MoonConnection.com All Rights Reserved. This moon phases diagram is NOT public domain and may not beused on websites, copied, printed or republished except by permission.

Diagram Explanation

The illustration may look a little complex at first, but it's easy to explain.

Sunlight is shown coming in from the right. The earth, of course, is at the center of the diagram. The

moon is shown at 8 key stages during its revolution around the earth. The moon phase name is shown

alongside the image. The dotted line from the earth to the moon represents your line of sight

when looking at the moon. To help you visualize how the moon would appear at that point in the

cycle, you can look at the larger moon image. This means for the waning gibbous, third

quarter, and waning crescent phases you have to mentally turn yourself upside down.

When you do this, you'll "see" that the illuminated portion is on your left, just as you see in the large

image.

One important thing to notice is that exactly one half of the moon is always illuminated by the sun. Of

course that is perfectly logical, but you need to visualize it in order to understand the phases. At

certain times we see both the sunlit portion and the shadowed portion -- and that creates the various

moon phase shapes we are all familiar with. Also note that the shadowed part of the moon is invisible

to the naked eye; in the diagram above, it is only shown for clarification purposes.

So the basic explanation is that the lunar phases are created by changing angles (relative positions) of

the earth, the moon and the sun, as the moon orbits the earth.

Moon Phases / Lunar Phases Explained http://www.moonconnection.com/moon_phases.phtml

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If you'd like to examine the phases of the moon more closely, via computer software, you may be

interested in this moon phases calendar software.

Moon Phases Simplified

It's probably easiest to understand the moon cycle in this order: new moon and full moon, first

quarter and third quarter, and the phases in between.

As shown in the above diagram, the new moon occurs when the moon is positioned between the

earth and sun. The three objects are in approximate alignment (why "approximate" is explained

below). The entire illuminated portion of the moon is on the back side of the moon, the half that we

cannot see.

At a full moon, the earth, moon, and sun are in approximate alignment, just as the new moon, but

the moon is on the opposite side of the earth, so the entire sunlit part of the moon is facing us. The

shadowed portion is entirely hidden from view.

The first quarter and third quarter moons (both often called a "half moon"), happen when the

moon is at a 90 degree angle with respect to the earth and sun. So we are seeing exactly half of the

moon illuminated and half in shadow.

Once you understand those four key moon phases, the phases between should be fairly easy to

visualize, as the illuminated portion gradually transitions between them.

An easy way to remember and understand those "between" lunar phase names is by breaking out and

defining 4 words: crescent, gibbous, waxing, and waning. The word crescent refers to the phases

where the moon is less that half illuminated. The word gibbous refers to phases where the moon is

more than half illuminated. Waxing essentially means "growing" or expanding in illumination, and

waning means "shrinking" or decreasing in illumination.

Thus you can simply combine the two words to create the phase name, as follows:

After the new moon, the sunlit portion is increasing, but less than half, so it is waxing crescent.

After the first quarter, the sunlit portion is still increasing, but now it is more than half, so it is waxing

gibbous. After the full moon (maximum illumination), the light continually decreases. So the waning

gibbous phase occurs next. Following the third quarter is the waning crescent, which wanes until

the light is completely gone -- a new moon.

The Moon's Orbit

You may have personally observed that the moon goes through a complete moon phases cycle in

about one month. That's true, but it's not exactly one month. The synodic period or lunation is

exactly 29.5305882 days. It's the time required for the moon to move to the same position (same

phase) as seen by an observer on earth. If you were to view the moon cycling the earth from outside

our solar system (the viewpoint of the stars), the time required is 27.3217 days, roughly two days

less. This figure is called the sidereal period or orbital period. Why is the synodic period different

from the sidereal period? The short answer is because on earth, we are viewing the moon from a

moving platform: during the moon cycle, the earth has moved approximately one month along its

year-long orbit around the sun, altering our angle of view with respect to the moon, and thus altering

the phase. The earth's orbital direction is such that it lengthens the period for earthbound observers.

Although the synodic and sidereal periods are exact numbers, the moon phase can't be precisely

calculated by simple division of days because the moon's motion (orbital speed and position) is

affected and perturbed by various forces of different strengths. Hence, complex equations are used to

determine the exact position and phase of the moon at any given point in time.

Also, looking at the diagram (and imagining it to scale), you may have wondered why, at a new

moon, the moon doesn't block the sun, and at a full moon, why the earth doesn't block sunlight from

reaching the moon. The reason is because the moon's orbit about the earth is about 5 degrees off

from the earth-sun orbital plane.

However, at special times during the year, the earth, moon, and sun do in fact "line up". When the

moon blocks the sun or a part of it, it's called a solar eclipse, and it can only happen during the new

moon phase. When the earth casts a shadow on the moon, it's called a lunar eclipse, and can only

happen during the full moon phase. Roughly 4 to 7 eclipses happen in any given year, but most of

them minor or "partial" eclipses. Major lunar or solar eclipses are relatively uncommon.

Moon Software

If you want to follow the phases of the moon, you should definitely take a look at QuickPhase Pro, our

flagship moon software product for your personal computer. This attractive and fun software covers

thousands of years of past and future moon phases and is easy to use.


2 of 3 9/18/2012 7:53 PM

Tools

Moon Software

Moon Phases Calendar

Current Moon Phase

Moon Phase Module

iGoogle Moon Gadget

Gravity On The Moon

Featured

Moon PhasesExplained

Moon Trading

Fishing By Moon Phase

Moon Phase Hunting

Night Photography

Moon Phase LessonPlan

Moon Glossary

Topics

Tides Explained

One Side of Moon

Moon Facts

Apollo Missions

Apollo 13

Apollo 11

Moon Landing Hoax

School Moon Activity

Astrological Moon Sign

The Moon Cycle

Lunar Eclipse

Solar Eclipse

Lunar vs Solar Eclipse

Apogee and Perigee

Earthshine

Full Moon Names

Harvest Moon

Blue Moon

The Moon Diet

Products

We Recommend

Moon Shop

Moon Posters

The Ocean's Tides Explained

Almost everyone is aware of the role that gravity plays in our lives. Not only does it keep our feet

planted firmly on the ground, but it also keeps order in the solar system. The gravitational forces

associated with the Sun and the planets interact to describe the orbits that we are familiar with, as

well as keep the Moon trapped in orbit around the Earth. These forces aren't only limited to managing

the dynamics of the celestial bodies, however. Gravity also has a more directly observable influence

on our planet. Specifically, gravitational forces are responsible for the rise and fall of the ocean's tides

all over the world.

The two primary agents when it comes to the motion of the ocean are the Sun and the Moon. Since

the gravitational influence of an object is directly related to its mass, the Sun has a definite advantage

over the moon when it comes to the strength of its forces. However, since the Sun is over 380 times

farther away from the Earth than the Moon, the smaller mass in orbit around us is able to exert its

effects on us much more strongly than the star.

The key when it comes to understanding how the tides work is to understand the relationship between

the motion of our planet and its moon. Both the Moon and the Earth are constantly moving through

space. Since the Earth spins on its own axis, water is kept balanced on all sides of the planet through

centrifugal force. The Moon's gravitational forces are strong enough to disrupt this balance by

accelerating the water towards the Moon. This causes the water to 'bulge.' The Earth's rotation causes

a sympathetic bulge on the opposite side of the planet as well. The areas of the Earth where the

bulging occurs experience high tide, and the others are subject to a low tide. However, the Moon's

movement around the Earth means that the effects of its forces are in motion as well, and as it

encircles our planet, this bulge moves with it.

The height of the tides can vary during the course of a month, due to the fact that the Moon is not

always the same distance from the Earth. As the Moon's orbit brings it in closer proximity to our

planet (closest distance within a moon cycle is called perigee), its gravitational forces can increase by

almost 50%, and this stronger force leads to high tides. Likewise, when the Moon is farther away from

the Earth (furthest distance is called apogee), the tides are not as spectacular.

The Moon's influence can also be balanced out by the position of the Sun – if the Sun and the Moon

find themselves 90 degrees apart in relation to an observer on the Earth, then high tides are not as

high as they normally would be. This is because despite its greater distance from the planet, the Sun's

mass allows it to exert enough gravitational force on the oceans that it can negate some of the effects

of the Moon's pull. This phenomenon of lower high tides is called a neap tide. In the same way, when

the Sun lines up with the Moon and the Earth, as during a Full Moon, then the Sun can act to amplify

the tidal forces, drawing even higher tides. These are known as spring tides, named not for the

season, but for the fact that the water "springs" higher than normal. The variance in the height of the

world's tides also depends on the local geography of the coastline and the topography of the ocean

floor.

Tides occur regularly in the sense that they can be expected twice a day, but their periods do not

coincide with the 24 hour day that we use for our calendar. This is because the Moon takes slightly

longer than 24 hours to line up again exactly with the same point on the Earth - about 50 minutes

more. Therefore, the timing of high tides is staggered throughout the course of a month, with each

tide commencing approximately 24 hours and 50 minutes later than the one before it.

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1 of 1 9/18/2012 7:54 PM

Types of Eclipse and Definition of an Eclipse

There are two primary types of eclipse which can be viewed from Earth, a Lunar Eclipse and a Solar

Eclipse

Definition of an Eclipse

An eclipse is the total or partial obscuring of one celestial body by another. It may occur when one

celestial body passes in front of another therefore cutting off some or all of its light. It may also occur

when a celestial body passes through all or part off the shadow of another celestial body.

Types of Eclipse -Earth - Moon - Sun system - Lunar Eclipses and Solar Eclipses

Eclipses of the Sun / Solar Eclipse - There are four types of solar eclipse - A Solar eclipse can be Total,

Annular, Partial or Hybrid

Eclipse of the Moon / Lunar Eclipses - Astronomers recognise three basic types of lunar eclipse - Total,

Partial and Penumbral

However there is a rare forth variation known as a Total Penumbral Lunar Eclipse

Total Lunar Eclipse

Eclipse of the Moon (or Lunar Eclipse). A lunar Eclipse is when the Earth is between the Sun and Moon and only occurs if the Moon passes through all or some portion of Earth's umbra shadow therefore blocking sunlight directly striking the Moon’s surface. This can occur only when the Sun, Earth, and Moon are aligned exactly, or almost exactly.

Eclipse of the Moon, or Lunar Eclipse

An eclipse of the Moon, or lunar eclipse, is when the Earth is between the Sun and Moon and only

occurs if the Moon passes through all or some portion of Earth's umbra shadow therefore blocking

sunlight directly striking the Moon’s surface. This can occur only when the Sun, Earth, and Moon are

aligned exactly, or almost exactly.

A lunar eclipse occurs at night and only when there is a Full Moon. A lunar eclipse can last for many

hours, and can be seen from the entire night side of the Earth and looks the same to everyone.

Total Solar Eclipse

Eclipse of the Sun, or Solar Eclipse; a solar eclipse is when the Moon is between the Sun and Earth and only occurs when the Moon is at just the right distance and angle in the sky to cover the Sun, this can only occur when the Sun, Moon and Earth are exactly aligned producing a Total Solar Eclipse.

An amazing coincidence that Total Solar Eclipses actually occur

Eclipse of the Sun, or Solar Eclipse

An eclipse of the Sun, or a solar eclipse, is when the Moon is between the Sun and Earth and only occurs

when the Moon is at just the right distance and angle in the sky to cover the Sun, this can only occur

when the Sun, Moon and Earth are exactly aligned producing a Total Solar Eclipse. The Moon also has to

be at or near one of its nodes; a node is simply the point at which the Moon crosses the eliptic from

south to north or vice versa as it orbits the Earth.

A Total Solar Eclipse occurs during daytime and only when there is a New Moon. A solar eclipse duration

is short with totality lasting from a few secounds to a few minutes. A Total Solar Eclipse is only seen by a

minority of people along a narrow corridor and appears different according to ones location and

distance from the central track of totality.

The Sun is 400 times the Moon's diameter, and 400 times as far away

It is an amazing coincidence that total solar eclipses actually occur. It is all due to size and distance

between all three celestial bodies of the Sun, Moon and Earth; all being (as the Goldilocks Principle says)

it's just right.

The Sun is 400 times the Moon's diameter and 400 times as far away. This means that the Sun and

Moon appear to have the same apparent size in the sky when viewed from Earth; both having

approximately the same degree of 0.5 arc in angular measurement.

A Total Solar Eclipse only occurs when the Moon is at or very near perigee (closest distance to Earth) and

all three bodies of the Sun, Moon, and Earth are in alignment. When the Moon is at apogee (furthest

distance from Earth) it is 11% more distant from Earth than it is a perigee, this makes the apparent size

of the Moon slightly smaller in diameter. The difference is small but is enough to change the

characteristics of a solar eclipse, resulting in that even if all three bodies of the Sun, Moon and Earth are

in perfect alignment, the Moon’s diameter still remains too small to cover the disc of the Sun and an

annular eclipse will occur.

The Moon also has to be at one of its nodes; a node is simply the point at which the Moon crosses the

eliptic as it orbits the Earth. The orbit of the Moon around Earth is inclined at approximately about 5.1°

to Earth's orbit around the Sun. As a consequence, the Moon's orbit crosses the ecliptic at two points /

nodes two times every month, The ascending node is when the Moon crosses from the south to the

north side of the ecliptic. The descending node is when the Moon crosses from the north to the south

side of the ecliptic..

Penumbral Lunar Eclipse

In essence most penumbral lunar eclipses are actually partial penumbral eclipses with only part of the

Moon passing through Earth’s penumbra shadow with the remaining section of the Moon staying

outside.

Although astronomers recognise three main types of lunar eclipse - those being; total, partial, and

penumbral, there is another rare variation of a penumbral eclipse known as a Total Penumbral Eclipse.

Rare Total Penumbral Eclipse

A Total Penumbral Eclipse occurs when the whole of the Moon is completely immersed in the penumbra

shadow of the Earth - with the Moon passing entirely within the penumbra cone of Earth without

touching the any part of Earth’s deeper umbra shadow. A Total Penumbral Eclipse is rare because the

penumbra shadow cast by Earth is about as wide as the Moon itself. About 1.2% of all lunar eclipses are

Total Penumbral Eclipses.

Although Total Penumbra Eclipses are rare there is only a slight tone change in the Moon’s appearance.

The side-by-side comparison of a Total Penumbra Eclipse makes it fairly easy to spot the slight tone

change to the Moon’s northern hemisphere, but the mid and southern hemisphere of the Moon is

almost indistinguishable. Observing live, even with a telescope, can be difficult to spot any variation as

there is nothing with which to compare.

Selenehelion or Selenelion Phenomena – sometimes called a Horizontal Eclipse

Lunar eclipses occurring just before sunrise or just after sunset produce an amazing phenomenon

A Selenehelion or selenelion event occurs during a Lunar Eclipse and can only be viewed just before

sunset or just after sunrise when it is possible to simultaneously view the sun rising in the east and the

eclipsed full moon setting in the west, both at the same time, appearing just above the horizon at

opposite points in the sky. This has led to the event sometimes being referred to as a Horizontal Eclipse.

It occurs during every lunar eclipse at all those places on the Earth where it is sunrise or sunset at the

time of the eclipse. The reddened light that reaches the Moon comes from all the simultaneous sunrises

and sunsets on the Earth and from the atmosphere of Earth bending light inwards towards the Moon.

The phenomena is not a type of eclipse, nor a sub classification of any type of eclipse, it is simple a

phenomena which occurs during a lunar eclipse just before sunset or just after sunrise.

This phenomenon may seem like an impossibility - to be able to see both the Sun and Moon in the sky at

the same time during a lunar eclipse. How is it possible? Depending on the observer’s location there is

short window of one to a few minutes when it is possible to simultaneously view the sun rising in the

east and the eclipsed full moon setting in the west. One or both bodies may actually be below the

horizon but atmospheric refraction causes astronomical objects to appear higher in the sky than they

are in reality.

A selenehelion phenomenon is best observed from high ground with clear unobstructed vision towards

both ends of the horizon. Hills, mountains, or high ridges are all good vantage points to view this

spectacular sight.

Diameter of Sun; 1,392,684km / 865,374 miles. Diameter of Moon; 3,476km / 2,159 miles. Although the Sun is much

bigger than the Moon they both have the same apparant size in the sky as viewed from the surface of Earth both

having approximately the same degree of 0.5 arc in angular measurement

Diameter of the Sun; 1,392,684km / 865,374 miles

Diameter of the Moon; 3,476km / 2,159 miles

Although the Sun is much bigger than the Moon they

both have the same apparant size in the sky both

having approximately the same degree of 0.5 arc in

angular measurement.

Other Planets and Moons can also have Eclipses - The moons of Mars - Phobos and Demois

Mars two moons - Phobos and Deimos

Phobos is approximately 21km / 13 miles in diameter and orbits Mars in 7 hours, 39.2 minutes. A

Martian day is 24 hours 37 minutes long and due to the rapid motion of Phobos, when conditions are

correct, Phobos can create two eclipses per Martian day / Sols. The event is nevertheless still classified

as an annular eclipse. An observer on the surface of Mars would never experience a solar eclipse for

longer than about thirty seconds.

Deimos's diameter is approximately 12km / 7.5 miles and is too small and too far from Mars to cause an

eclipse of any significance. The best an observer on Mars would see is a small object in transit across the

surface of the Sun. Deimos would appear about as bright as the planet Venus looks from Earth and

approximately the same size.

Mars does not have spectacular eclipses as occur on Earth and the motion of Deimos is regarded more

of a transit rather than a true eclipse as observed from the surface of Mars. from the surface.

Et Cetera

Some key concepts/vocabulary not specifically addressed in other places.

Difference between rotation (above left) and revolution (above right).

Astronomical Unit (AU):

• approximately 93 million miles

• distance from the Sun to the Earth

• common measurement unit for distances within the solar system

Tilt of Earth's Axis = 23.5 degrees

Chapter 5: Life Science

What are the five characteristics of living things?

Read: Classification of Living an Non-Living Things

What are photosynthesis, transpiration, respiration?

Read: Plants

How do plants reproduce? What is the difference between reproduction: sexual (germination, fertilization) and asexual (bulbs, roots, cuttings)?

Read: Plant Reproduction

How do plant cells differ from animal cells? Some of the key elements include nucleus, cytoplasm, chromosomes, cell membrane, vacuole, chloroplasts.

Read: Plant and Animal Cells

http://www.ehow.com/facts_5790374_difference-between-living-non_living-organi

http://www.ext.colostate.edu/mg/gardennotes/141.html

http://teachers.greenville.k12.sc.us/sites/brooks/Plants/Plant%20Reproduction%20Notes.pdf

http://www.wisegeek.com/what-are-some-differences-between-plant-and-animal-c

The line between living and non-living things isn't always so clear. Not all living

things exhibit every commonly accepted "life" characteristic, and some non-living

things have characteristics of living organisms.

All living things grow. Animals stop growing when they reach maturity, while

plants grow indefinitely for the duration of their lives.

Living organisms all have some form of respiration that is carried out within and

regulated by their own bodies.

Living things can reproduce themselves. They pass on their genetic information to

their offspring, ensuring the propagation of their species.

Non-living things cannot move under their own power, whereas all living things

can move deliberately. Even plants, which seem stationary, can turn themselves to

Print Article

Discover the expert in you.

Difference Between Living & Non-Living

OrganismsBy Jessica Martinez, eHow Contributor

The simplest classification of objects is that of living and non-living. By

definition, only living things are considered to be organisms. Scientists have

developed a number of criteria for determining whether or not something can in

fact be considered a living being.

Considerations

Growth

Respiration

Reproduction

Movement

Difference Between Living & Non-Living Organisms | eHow.com http://www.ehow.com/print/facts_5790374_difference-between-living-no...

1 of 2 9/18/2012 8:00 PM

better reach the sun.

Non-living things can neither respond nor adapt to their environment. They can be

altered by external forces in their environment, but only living things can change

their habits or metabolisms to adapt to ambient changes.

Environmental Adaptation and Response

ResourcesRead this Article in Spanish

Read this Article in UK English

Difference Between Living & Non-Living Organisms | eHow.com http://www.ehow.com/print/facts_5790374_difference-between-living-no...

2 of 2 9/18/2012 8:00 PM

141-1

Colorado Master Gardenersm Program Colorado Gardener Certificate Training Colorado State University Extension CMG GardenNotes #141 Plant Physiology: Photosynthesis, Respiration, and Transpiration

Outline: Photosynthesis, page 1 Respiration, page 2 Transpiration, page 3

The three major functions that are basic to plant growth and development are:

• Photosynthesis – The process of capturing light energy and converting it to sugar energy, in the presence of chlorophyll using carbon dioxide (CO2) and water (H2O).

• Respiration – The process of metabolizing (burning) sugars to yield energy for growth, reproduction, and other life processes

• Transpiration – The loss of water vapor through the stomata of leaves Photosynthesis

A primary difference between plants and animals is the plant’s ability to manufacture its own food. In photosynthesis, carbon dioxide from the air and water from the soil react with the sun’s energy to form photosynthates (sugars, starches, carbohydrates, and proteins) and release oxygen as a byproduct. [Figure 1]

Figure 1. In photosynthesis, the plant uses water and nutrients from the soil, and carbon dioxide from the air, with the sun’s energy to create photosynthates. Oxygen is releases as a byproduct.

Thought question Explain the science behind the following question

1. What’s the impact on air temperatures when restrictions in

landscape irrigation create droughty urban landscapes?

141-2

Photosynthesis literally means to put together with light. It occurs only in the chloroplasts, tiny sub-cellular structures contained in the cells of leaves and green stems. A simple chemical equation for photosynthesis is given as follows:

carbon dioxide + water + light energy = glucose + oxygen 6CO2 + 6H2O + light energy = C6H12O6 + 6O2 .

This process is directly dependent on the supply of water, light, and carbon dioxide. Limiting any one of the factors on the left side of the equation (carbon dioxide, water, or light) can limit photosynthesis regardless of the availability of the other factors. An implication of drought or severe restrictions on landscape irrigation is a reduction in photosynthesis and thus a decrease in plant vigor and growth. In a tightly closed greenhouse there can be very little fresh air infiltration and carbon dioxide levels can become limiting, thus limiting plant growth. In the winter, many large commercial greenhouses provide supplemental carbon dioxide to stimulate plant growth. The rate of photosynthesis is somewhat temperature dependent. For example, with tomatoes, when temperatures rise above 96°F the rate of food used by respiration rises above the rate of which food is manufactured by photosynthesis. Plant growth comes to a stop and produce loses its sweetness. Most other plants are similar. [Figure 2]

Figure 2. For the tomato plant, rates of photosynthesis and respiration both increase with increasing temperatures. As the temperature approaches 96°F, the rate of photosynthesis levels off, while the rate of respiration continues to rise.

Respiration

In respiration, plants (and animals) convert the sugars (photosynthates) back into energy for growth and other life processes (metabolic processes). The chemical equation for respiration shows that the photosynthates are combined with oxygen releasing energy, carbon dioxide, and water. A simple chemical equation for respiration is given below. Notice that the equation for respiration is the opposite of that for photosynthesis.

glucose + oxygen = energy + carbon dioxide + water C6H12O6 + 6O2 = energy + 6CO2 + 6H2O

Chemically speaking, the process is similar to the oxidation that occurs as wood is burned, producing heat. When compounds combine with oxygen, the process is

141-3

often referred to as “burning”, for example, athlete’s “burn” energy (sugars) as they exercise. The harder they exercise, the more sugars they burn so the more oxygen they need. That is why at full speed, they are breathing very fast. Athletes take up oxygen through their lungs. Plants take up oxygen through the stomata in their leaves and through their roots. Again, respiration is the burning of photosynthates for energy to grow and to do the internal “work” of living. It is very important to understand that both plants and animals (including microorganisms) need oxygen for respiration. This is why overly wet or saturated soils are detrimental to root growth and function, as well as the decomposition processes carried out by microorganisms in the soil.

The same principles regarding limiting factors are valid for both photosynthesis and respiration.

Comparison of photosynthesis and respiration Photosynthesis Respiration

Produces sugars from energy Burns sugars for energy Energy is stored Energy is released Occurs only in cells with chloroplasts Occurs in most cells Oxygen is produced Oxygen is used Water is used Water is produced Carbon dioxide is used Carbon dioxide is produced Requires light Occurs in dark and light

Transpiration

Water in the roots is pulled through the plant by transpiration (loss of water vapor through the stomata of the leaves). Transpiration uses about 90% of the water that enters the plant. The other 10% is an ingredient in photosynthesis and cell growth. Transpiration serves three essential roles:

• Movement of minerals up from the root (in the xylem) and sugars (products of photosynthesis) throughout the plant (in the phloem). Water serves as both the solvent and the avenue of transport.

• Cooling – 80% of the cooling effect of a shade tree is from the evaporative cooling effects of transpiration. This benefits both plants and humans.

• Turgor pressure – Water maintains the turgor pressure in cells much like air inflates a balloon, giving the non-woody plant parts form. Turgidity is important so the plant can remain stiff and upright and gain a competitive advantage when it comes to light. Turgidity is also important for the functioning of the guard cells, which surround the stomata and regulate water loss and carbon dioxide uptake. Turgidity also is the force that pushes roots through the soil.

Water movement in plants is also a factor of osmotic pressure and capillary action. Osmotic pressure is defined as water flowing through a permeable membrane in the direction of higher salt concentrations. Water will continue to flow in the direction of the highest salt concentration until the salts have been diluted to the point that the concentrations on both sides of the membrane are equal.

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A classic example is pouring salt on a slug. Because the salt concentration outside the slug is highest, the water from inside the slug’s body crosses the membrane that is his "skin”. The poor slug becomes dehydrated and dies. Envision this same scenario the next time you gargle with salt water to kill the bacteria that are causing your sore throat. Fertilizer burn and dog urine spots in a lawn are examples of salt problems. The salt level in the soil’s water becomes higher than in the roots, and water flows from the roots into the soil’s water in an effort to dilute the concentration. So what should you do if you accidentally apply too much fertilizer to your lawn? Capillary action refers to the chemical forces that move water as a continuous film rather than as individual molecules. Water molecules in the soil and in the plant cling to one another and are reluctant to let go. You have observed this as water forms a meniscus on a coin or the lip of a glass. Thus when one molecule is drawn up the plant stem, it pulls another one along with it. These forces that link water molecules together can be overcome by gravity.

Additional Information – CMG GardenNotes on How Plants Grow (Botany):

#121 Horticulture Classification Terms #136 Plant Structures: Fruit #122 Taxonomic Classification #137 Plant Structures: Seeds #131 Plant Structures: Cells, Tissues, #141 Plant Growth Factors: Photosynthesis,

and Structures Respiration and Transpiration #132 Plant Structures: Roots #142 Plant Growth Factors: Light #133 Plant Structures: Stems #143 Plant Growth Factors: Temperature #134 Plant Structures: Leaves #144 Plant Growth Factors: Water #135 Plant Structures: Flowers #145 Plant Growth Factors: Hormones

o Authors: David Whiting, Consumer Horticulture Specialist, Colorado State University Extension; with Michael Roll and Larry

Vickerman (former CSU Extension employees). Line drawings by Scott Johnson and David Whiting.

o Colorado Master Gardener GardenNotes are available online at www.cmg.colostate.edu. o Colorado Master Gardener training is made possible, in part, by a grant from the Colorado Garden Show, Inc. o Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. o Extension programs are available to all without discrimination. o No endorsement of products mentioned is intended nor is criticism implied of products not mentioned. o Copyright 2003-2010. Colorado State University Extension. All Rights Reserved. CMG GardenNotes may be reproduced,

without change or additions, for nonprofit educational use.

Minor Revisions December 2011

Plant Reproduction

Sexual and Asexual Reproduction in Flowering Plants Two Types of Reproduction in Plants

� Sexual reproduction is a process that involves two parent plants to form a new organism which differs from both parents.

� Asexual reproduction is a process that involves only one parent plant and produces offspring identical to the parent plant.

Sexual Reproduction: Life Cycle

All flowering plants have similar life cycles. The 4 main stages of a plant’s life cycle are:

� Germination � Plant development � Fertilization � Seed Production

Reproduction in Angiosperms

� First, pollen falls on a flower’s stigma. In time, the sperm cell and egg cell join together in the flower’s ovule. The zygote develops into the embryo part of the seed.

Sexual Reproduction: Germination

� Germination is the early stage of seed growth. � Germination begins when the seed absorbs water from the

environment. Water is the main ingredient for germination to occur.

� During germination, the roots begin to grow down, while the stem and leaves grow up (gravitropism).

Sexual Reproduction: Plant Development

� Plant development is when the seed grows into a mature plant.

� During plant development, the plant develops the structures necessary to produce more plants.

� These reproductive structures are called flowers. Sexual Reproduction: Fertilization

� Fertilization is the joining of a sperm cell (pollen) and an egg cell (ovule).

� The transfer of pollen from the male part of the plant (stamen) to the female part (pistil) of the plant is called pollination.

� The 4 ways that pollination can occur are wind, birds, bats, and insects.

Sexual Reproduction: Flowers

� Flowers are the reproductive structures of some plants. � In order to attract pollinators (birds, bats, or insects),

flowers often have colorful petals or produce a scent. The Structure of Flowers The Structure of a Flower Activity Sexual Reproduction: Flowers

� Flowers have male and female parts. � The male part is called the stamen and consists of:

� Filament - thin stalk � Anther - knob at top of stalk

Sexual Reproduction: Flowers

� The female part is called the pistil and consists of: � Stigma - sticky top where pollen grains land � Style - stalk down which pollen tube grows � Ovary - contains the ovule (egg cell)

Sexual Reproduction: Seed Production

� Seeds are structures that contain a young plant inside a protective covering.

� The protective covering is called a seed coat. Sexual Reproduction: Fruits

� Plants produce fruits to help disperse their seeds. � The ways that plants disperse their seeds:

� Animals : fur (“hitch hikers”), burying seeds and ingestion of fruit

� Water: Coconuts � Wind: Cotton plants, Dandelions � Exploding pods: Witch hazel, Wisteria

Asexual Reproduction: When and Why?

� Plants do not naturally reproduce asexually. � Plants reproduce asexually when there are no

partners nearby or when they are damaged. � The main advantage of sexual reproduction is that

the best traits of both partners can be used in the new organism (offspring).

Asexual Reproduction: Vegetative Propagation

� Vegetative propagation is the process of growing new plants from plant parts.

� 5 plant parts used for vegetative propagation: � Bulbs � Runners � Stem cuttings � Roots � Leaves

Asexual Reproduction: Bulbs

� Bulbs are underground stems. � Bulbs are big, round buds made of a stem and special

types of leaves. � Bulbs are not connected to the parent. � Examples:

� Onion � Tulip � Iris

Asexual Reproduction: Runners

� Runners are stems that run along the ground. � Runners are long and skinny. � Runners are connected to the parent. � Examples:

� Grass (centipede) � Ivy � Strawberries

Asexual Reproduction: Stem Cuttings

� When a piece of cut stem is planted, roots may form from the cutting. Then a full plant develops.

� Examples: � Sugar cane � Pineapple

Asexual Reproduction: Roots

� Roots send out new shoots, called “suckers”. � Some plants can produce new plants from root pieces. � Examples:

� Fruit trees � Sweet potatoes

Asexual Reproduction: Leaves

� Some houseplants produce little plants right on their leaves.

� Examples: � African violets

Life Cycle of plants

� Annuals are plants that complete their entire life cycle in one year

� Biennials are plants that complete their entire life cycle in two years

� Perennials are plants that take more than two years to grow to maturity and complete their life cycle

How Are Animal Cells Different from Plant CellsFiled under: Animal Cells - 11 Jul 2012 | Spread the word !

Cells are the functional and structural units of all living organisms. Both plants and animals have them, but animal cells are different from plant cells in some respects. There are

certain characteristics that clearly set them apart, but essentially they are the same and share the same functions. Here are the main differences between them.

Source

Plant Cells

- have chloroplasts containing chlorophylls, meaning light-absorbing pigments that help them in the photosynthesis process, which enables them to make their own food;

- have a cell wall over the cell membrane, which supports a rigid, typically rectangular structure that is composed of cellulose, hemicellulose, and many other materials;

- are more square shaped;

- have a single large, central vacuole that usually takes up 90% of cell volume;

- have plasmodesmata, which are microscopic channels that traverse the cell walls and are considered to be communication pathways;

- do not have centrioles (except for lower plant forms).

Animal Cells

- do not have chloroplasts;

- do not have a cell wall; they only have the cell membrane;

- are either circular or irregular; as they do not have a cell wall, animal cells have more dynamic shapes, but they are mostly circular;

- have one or more vacuoles; even though there are many more vacuoles in the animal cell, they do not take up the volume that the central vacuole in plants does;

- do not have plasmodesmata;

- have centrioles; plants do not need to have these organelles, since their spindle fibers connect to the cell wall.

<iframe width=”560″ height=”315″ src=”http://www.youtube.com/embed/HO7w_bC1KJA” frameborder=”0″ allowfullscreen></iframe>

These are the main differences between plant and animal cells. Except for these particular features, they share the same organelles: endoplasmatic reticulum (smooth and

rough), ribosomes, mithochondria, Golgi apparatus, plasma membrane, microtubules and microfilaments, lysosomes, and nucleus. Flagella may be found is some cells, as well as

cilia. However, cilia is quite rare in plant cells.

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How are Animal Cells Different From Plant Cells

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