Post on 22-Dec-2015
Welcome to Physics 7A!
Lecturer: Cassandra PaulSlides will be available online at:
http://everest.physics.ucdavis.edu/physics7
Logistics
• Course Website: http://physics.ucdavis.edu/physics7/ (click on Physics 7A)
• Discussion/Lab meet daily Monday-Thursday, and attendance is mandatory. First DL is TODAY!
• Lecture meets Monday and Wednesday, attendance is also mandatory.
• Required Book College Physics: A Models Approach• Quizzes weekly: Quiz 1 is Wednesday! (Quiz 2 is a week
from today.)• Reading Assignments• Clickers: required and worth 5% of your grade (for
participation)
Setup Clickers
• Turn Clickers On• Select Class:• Scroll down in ‘Setup Menu’ until you see ‘ID’• Press the Green Arrow• Enter Student ID
Test Clickers
• Have you had Physics before?A. No, NoneB. Conceptual Physics Class (HS or College)C. Algebra Based High School ClassD. Algebra Based College CourseE. Calculus Based College Course
What is physics?Why is the sky blue?
What is “rainbow” really?
How does a light switch work?
Why does she start spinning so much faster when she pulls her arms and legs in? Why do planets orbit?
How do magnets work?
Can ice be colder than 0°C?
We begin with the child-like wonder about our everyday world.
As Physicists we...• Observe phenomena and ask questions
about them• Try to explain phenomena using a few
principles (models) - We cannot “pick and choose” when an
explanation “works”- We must have understanding of when a
model is valid and when it is not. (Understanding model limitations is AS important as understanding how the model works!)
Physics is taking this approach to explain phenomena in the physical world.
What is physics 7?Physics 7 is a 3-quarter series of physics classes, typically taken by bio-science and other non-physics science majors.
• Physics 7A: Energy conservation, thermodynamics, particle models of matter. • Physics 7B: Classical Mechanics, rotational motion, fluids, circuits. • Physics 7C: Wave phenomena, optics, electricity and magnetism, the atom and modern quantum mechanics.
How is Physics 7 different?• Less Emphasis on Lecture
– Less time in lecture than other courses– Never EVER tested on things you see ONLY in lecture
• Models– Physics comes from a few principles– We will be drawing a lot of diagrams and graphs
• Emphasis on Conceptual Understanding– No multiple choice questions on Quizzes or the Final– You are graded on the quality of your argument more than your ability to ‘calculate.’– Most equations will be provided
• Not Graded on Curve– No competition between classmates promotes ‘idea’ sharing
• Discussion Labs– All work is group work– You, your classmates will work together to obtain a better understanding of
Physics– Your TA is your guide, NOT your lecturer
Physics 7 is BETTER!RESEARCH shows that
Students that take Physics 7…
• Obtain a more conceptual understanding of Physics
AND• Perform better in later
courses
AND• Score better on their MCATS
…than students who took a traditional version of the course.
The first concept in 7A: EnergyWhat is Energy? • Energy is a thing (quantity or state function). It is a property of matter
and radiation, and we can think about it as the capacity to do work.• You & I contain energy, as do the chairs you sit on and the air we
breathe.
What are some forms of Energy? • Thermal Energy (Having to do with Temperature)• Kinetic Energy (movement)• Gravitational (potential energy)
Can we measure Energy? • We can calculate how much energy something has and• We can measure the transformation of energy (or change, E).
Conservation of EnergyConservation of Energy
Conservation of EnergyEnergy cannot be created nor destroyed, simply
converted from one form to another.
• If the energy of an object increases, something else must have given that object its energy.
• If it decreases, it has given its energy to something else. Energy transfer is done through Heat or Work.
Models in Physics 7AModels can help us organize our thinking,
can contain other models, and can be very useful. Models also have limitations: experiment is the final judge.
• Three-phase model of matter
• Energy-interaction model
• Mass-spring oscillator• Particle model of matter
Particle model of bond energy Particle model of thermal energy
• Thermodynamics• Ideal gas model• Statistical model of thermodynamics
We start withThese two…
Three-Phase model of Matter
• Solid: Keeps its shape without a container• Liquid: Takes the shape of the (bottom of)
the container. Keeps its volume the same.• Gas: Takes the shape and volume of the
container.
Example H2O
Three-Phase model of Matter
Q How do we change the phase of matter?
How do we change the temperature of matter?
A By adding or removing energy. Often this energy is transferred from, or to the substance as heat Q.
Example H2O
Temperature
Energy added or removed
liquid
gas
l-g coexist
s-l coexist
TMP
TBP
Three-Phase model of Matter
solid
Example: Melting ice initially at -10C, and bringing it to 15C
Temperature
Energy added
solid
liquid
gas
Initial
TMP
TBP
Final
T
T
T const
Energy Interaction DiagramsBased on the energy interaction model, it shows you how energy is transferred, how
energy is conserved between energy systems.
Energy systems:There are many different types of energies called energy
systems:
EEthermatherma
ll
EEbondbondEEmovementmovement
(KE)(KE)
EEgravitgravit
yy
EEelectrielectri
cc
EEsprinsprin
gg
........
For each energy system, there is an indicator that tells us how that energy system can change.
Ethermal: indicator is temperatureEbond: indicator is the initial and final phases
Energy-Interaction Model
Energy interaction diagrams - closed
EEaa EEbb EEcc
Conservation of EnergyThe total energy of a closed physical system must remain constant. In other words, the change of the energies of allenergy systems associated with the physical system must sum to zero.
Change in system energy = ∆Ea + ∆ Eb + ∆ Ec = 0
€ €
Energy interaction diagrams - open
EEaa EEbb EEcc
Conservation of EnergyThe change of the energies of all energy systems associated with an open physical system must sum to the net energy added/removed as heat or work.
Change in system energy = ∆Ea + ∆ Eb + ∆ Ec
= (Energy added) - (Energy removed) = Q+W
€ € Energy added Energy removed
Back to the example…
Melting ice initially at -10°C, and bringing it to 15°C
To set up the model:• Define system• Define interval• What indicators are changing?• What energies are changing?• How are they changing?• Is this an open or closed system?• What (if anything) is entering/leaving the system?• Write Energy Conservation Equation
The Energy Interaction Model
Ice
System: H2OInitial: Solid (Ice) at -10°CFinal: Liquid (Water) at 15°C
EEthermtherm
alalEEbondbond
EEthermtherm
alalT T
ml
T
I: T=-10°CF: T=0°C
HEAT
I: all solidF: all liquid
I: T=0°CF: T=15°C
ΔEths + ΔEbond + ΔEthl = Q
How can we model how much Energy is needed to melt ice initially at -10C, and bring it to 15C?
+ + + +
Mixed Water
Condensing Steam initially at 100°C to a final temperature of 40°C
Temperature
Energy added or removed
TMP
TBP
Initial
Final
Condensing Steam initially at 100°C to a final temperature of 40°C
To set up the Energy Interaction Model:• Define system• Define interval• What indicators are changing?• What energies are changing?• How are they changing?• Is this an open or closed system?• What (if anything) is entering/leaving the
system?• Write Energy Conservation Equation
Condensing Steam initially at 100°C to a final temperature of 40°C
EEthermtherm
alalEEbondbond
T
mg
I: T=100°CF: T=40°C
I: all gasF: all liquid
System: H2OInitial: Gas (steam) at 100°CFinal: Liquid (Water) at 40°C
WaterMixed
ΔEthl + ΔEbond = Q
HEAT