Review of the Review of the Scientific MethodScientific Method"The scientific method is nothing but "The scientific method is nothing but the normal working of the human the normal working of the human mind."mind."

Thomas HuxleyThomas Huxley

What is the Scientific What is the Scientific Method?Method?

The scientific method is a planned, The scientific method is a planned, logical, approach taken to solving a logical, approach taken to solving a problemproblem

It consists of asking a question, It consists of asking a question, developing a possible solution, testing developing a possible solution, testing the possible solution, recording data, and the possible solution, recording data, and analyzing resultsanalyzing results

Steps of the Scientific Steps of the Scientific MethodMethod

The basic scientific method consists of The basic scientific method consists of five broad steps:five broad steps:

Identifying the problem or questionIdentifying the problem or question Developing a possible solution, or Developing a possible solution, or

hypothesishypothesis Designing and executing a testDesigning and executing a test Collection and analysis of dataCollection and analysis of data The formulation of a conclusionThe formulation of a conclusion

Identifying the Problem Identifying the Problem or Questionor Question

Identify a problem to be solved or a questioned Identify a problem to be solved or a questioned to be answered.to be answered.

To be scientifically valid, questions or problems To be scientifically valid, questions or problems must be falsifiable.must be falsifiable.

Usually scientists collect information about a Usually scientists collect information about a problem or question, before positing a possible problem or question, before positing a possible solution.solution.

The possible solution to a scientific problem or The possible solution to a scientific problem or question is known as a question is known as a hypothesishypothesis

The HypothesisThe Hypothesis

A hypothesis is a possible solution to a scientific A hypothesis is a possible solution to a scientific problem or question.problem or question.

To be valid a hypothesis must be testableTo be valid a hypothesis must be testable Ex. Which of the following are valid hypotheses?Ex. Which of the following are valid hypotheses? The sky is blue due to the reflection of sunlight off the The sky is blue due to the reflection of sunlight off the

Earth’s oceans.Earth’s oceans. The sky is blue due to the scattering of blue light by The sky is blue due to the scattering of blue light by

oxygen in the atmosphere.oxygen in the atmosphere. The sky is blue because a higher being made it that The sky is blue because a higher being made it that

way.way.

Procedure: What is an Experiment?Procedure: What is an Experiment?

An experiment is a test designed to prove or An experiment is a test designed to prove or disprove a hypothesisdisprove a hypothesis

Experimental Design involves:Experimental Design involves: Establishing controlled and uncontrolled Establishing controlled and uncontrolled

variablesvariables Establishing the independent and dependent Establishing the independent and dependent

variables.variables. Experiments generate data which scientists Experiments generate data which scientists

record in tables, etc.record in tables, etc.

Collecting and Analyzing DataCollecting and Analyzing Data

• Data collection occurs as an experiment Data collection occurs as an experiment proceeds.proceeds.

• Usually data is numerical in formUsually data is numerical in form

• However, during an experiment However, during an experiment observations may be made that can observations may be made that can include temperature changes, the include temperature changes, the formation of gas bubbles, changes in formation of gas bubbles, changes in color, etc.color, etc.

Analysis of DataAnalysis of Data

Numerical Data is usually analyzed by Numerical Data is usually analyzed by determining the mean, median, and determining the mean, median, and mode.mode.

Numerical data is often graphed as a Numerical data is often graphed as a means of visually determining means of visually determining relationships between variables.relationships between variables.

ConclusionsConclusions

After the data is analyzed a After the data is analyzed a determination must be made as to determination must be made as to whether the data supports or refutes the whether the data supports or refutes the hypothesis.hypothesis.

If the data supports the hypothesis…If the data supports the hypothesis… If the data refutes the hypothesis…If the data refutes the hypothesis… If the data is indeterminate…If the data is indeterminate…

An Example of An Example of Experimental DesignExperimental Design

Francesco Redi Francesco Redi

Tests the Theory of Tests the Theory of

Spontaneous Spontaneous

GenerationGeneration

Background – Background – Spontaneous GenerationSpontaneous Generation

Until the seventeenth century experimentation Until the seventeenth century experimentation was treated as an art rather than science.was treated as an art rather than science.

Many strange, and now discredited, ideas Many strange, and now discredited, ideas about how living organisms are propagated about how living organisms are propagated flourished.flourished.

The theory of spontaneous generation was a The theory of spontaneous generation was a very popular, ancient theory used to explain very popular, ancient theory used to explain the seeming production of many animals from the seeming production of many animals from non-living materials.non-living materials.

Example OneExample One

ObservationObservation:: Every year in the spring, the Nile Every year in the spring, the Nile River flooded areas of Egypt along the river, River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. the people to grow that year’s crop of food. However, along with the muddy soil, large However, along with the muddy soil, large numbers of frogs appeared that weren’t around numbers of frogs appeared that weren’t around in drier times. in drier times.

ConclusionConclusion:: It was perfectly obvious to It was perfectly obvious to ancient peoples that the muddy soil gave rise ancient peoples that the muddy soil gave rise to the frogs. to the frogs.

Example Two:Example Two:

ObservationObservation:: In many parts of Europe, In many parts of Europe, medieval farmers stored grain in barns medieval farmers stored grain in barns with thatched roofs. As a roof aged, it with thatched roofs. As a roof aged, it was not uncommon for it to start leaking. was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, This could lead to spoiled or moldy grain, and of course there were lots of mice and of course there were lots of mice around. around.

ConclusionConclusion:: It was obvious to them that It was obvious to them that the mice came from the moldy grain.the mice came from the moldy grain.

Example ThreeExample Three Observation:Observation: Since there were no refrigerators, the Since there were no refrigerators, the

mandatory, daily trip to the butcher shop, especially in mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would customers selected which chunk the butcher would carve off for them. Many times they would have to carve off for them. Many times they would have to remove maggots from the putrefying meat.remove maggots from the putrefying meat.

Conclusion:Conclusion: Obviously, the rotting meat that had been Obviously, the rotting meat that had been hanging in the sun all day was the source of the hanging in the sun all day was the source of the maggots and fliesmaggots and flies

Redi’s ExperimentRedi’s Experiment

Francesco Redi (1626-1697), an Italian Francesco Redi (1626-1697), an Italian scientist, thought that the Theory of scientist, thought that the Theory of spontaneous Generation was incorrect.spontaneous Generation was incorrect.

In 1668 he designed what is thought to be the In 1668 he designed what is thought to be the first experiment explicitly designed via the first experiment explicitly designed via the scientific method. scientific method.

The experiment tested the idea that maggots, The experiment tested the idea that maggots, and therefore flies, are generated and therefore flies, are generated spontaneously from rotting meat.spontaneously from rotting meat.

Redi’s Problem and HypothesisRedi’s Problem and Hypothesis

Observation:Observation: There are flies around meat There are flies around meat carcasses at the butcher shop. carcasses at the butcher shop.

Question:Question: Where do the flies come from? Where do the flies come from? Does rotting meat turn into, or generate, the Does rotting meat turn into, or generate, the flies? flies?

Hypothesis:Hypothesis: Rotten meat does not turn into Rotten meat does not turn into flies. Only flies can make more flies. flies. Only flies can make more flies.

Prediction:Prediction: If meat cannot turn into flies, If meat cannot turn into flies, rotting meat in a sealed (fly-proof) container rotting meat in a sealed (fly-proof) container should not produce flies or maggots. should not produce flies or maggots.

Redi’s Test and Redi’s Test and ObservationsObservations

No Cover Cheesecloth Cover Impervious Cover

Data: Presence or absence of flies and maggots observed in each jar was recorded. In the control group of jars, flies were seen entering the jars. Later, maggots, then more flies were seen on the meat. In the gauze-covered jars, no flies were seen in the jars, but were observed around and on the gauze, and later a few maggots were seen on the meat. In the sealed jars, no maggots or flies were ever seen on the meat.

Redi’s ConclusionsRedi’s Conclusions

Only flies can make more flies.Only flies can make more flies. In the uncovered jars, flies entered and laid eggs on In the uncovered jars, flies entered and laid eggs on

the meat. Maggots hatched from these eggs and grew the meat. Maggots hatched from these eggs and grew into more adult flies. into more adult flies.

Adult flies laid eggs on the gauze on the gauze-Adult flies laid eggs on the gauze on the gauze-covered jars. Maggots appeared on the gauze. covered jars. Maggots appeared on the gauze.

In the sealed jars, no flies, maggots, nor eggs could In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. enter, thus none were seen in those jars.

Maggots arose only where flies were able to lay eggs. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous This experiment disproved the idea of spontaneous generation for larger organisms.generation for larger organisms.

Controlled Versus Controlled Versus Uncontrolled VariablesUncontrolled Variables

A A controlled variablecontrolled variable is any factor in an is any factor in an experiment that is kept the same in all trials of experiment that is kept the same in all trials of the experiment. the experiment.

Controlled variables are more commonly Controlled variables are more commonly known as known as Constants.Constants.

Uncontrolled variablesUncontrolled variables are those factors in an are those factors in an experiment that are allowed, or chosen, to experiment that are allowed, or chosen, to change during the experiment.change during the experiment.

There are two types of uncontrolled variables: There are two types of uncontrolled variables: IndependentIndependent and and DependentDependent

Independent versus Independent versus Dependent VariablesDependent Variables

The The independent variable (aka: manipulated independent variable (aka: manipulated variable)variable) is the factor in an experiment that is is the factor in an experiment that is chosen, or manipulated by the experimenter.chosen, or manipulated by the experimenter.

What was the independent variable in Redi’s What was the independent variable in Redi’s experiment?experiment?

The The dependent variable (aka: responding or dependent variable (aka: responding or measured variable)measured variable) in an experiment is the in an experiment is the factor that changes or responds to changes in factor that changes or responds to changes in the independent variable. the independent variable.

What was the dependent variable in Redi’s What was the dependent variable in Redi’s experiment?experiment?

Control Group versus Experimental Control Group versus Experimental GroupGroup

The The control groupcontrol group in an experiment is the set of tests in an experiment is the set of tests in which nothing was manipulated by the experimenter.in which nothing was manipulated by the experimenter.

The control group is the standard by which all changes The control group is the standard by which all changes in the manipulated tests are measured.in the manipulated tests are measured.

What was the control group in Redi’s experiment?What was the control group in Redi’s experiment? The The experimental groupexperimental group in an experiment is the set of in an experiment is the set of

tests in which the experimenter manipulates the tests in which the experimenter manipulates the independent variable.independent variable.

What was the experimental group in Redi’s What was the experimental group in Redi’s Experiment?Experiment?

Identifying Controls Identifying Controls and Variablesand Variables

Smithers thinks that a special juice will increase the Smithers thinks that a special juice will increase the productivity of workers. productivity of workers.

He creates two groups of 50 workers each and He creates two groups of 50 workers each and assigns each group a task (in this case they’re assigns each group a task (in this case they’re supposed to staple a set of papers). supposed to staple a set of papers).

Group A is given the special juice to drink while they Group A is given the special juice to drink while they work. Group B is not given anything. work. Group B is not given anything.

After one hour Smithers counts how many stacks of After one hour Smithers counts how many stacks of papers each group has made. Group A made 1,587 papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks.stacks, Group B made 2,113 stacks.

Identifying Controls Identifying Controls and Variablesand Variables

What was Smithers’ ……What was Smithers’ …… Control Group?Control Group? Independent Variable?Independent Variable? Dependent Variable?Dependent Variable? What should Smithers’ conclusion be?What should Smithers’ conclusion be? How could Smithers’ improve his experiment?How could Smithers’ improve his experiment?

Assignment:Assignment:

Work in pairs to complete “The Simpsons Work in pairs to complete “The Simpsons Identifying Controls and Variables” Identifying Controls and Variables” worksheet. worksheet.

If you do not finish the assignment in If you do not finish the assignment in class complete it as home work.class complete it as home work.

Yesterday’s Yesterday’s Classwork/HomeworkClasswork/Homework

Identifying Experimental Variables and CIdentifying Experimental Variables and Controlsontrols