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 do you think of when you hear the word Physics?

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.

Something to Keep in Mind…

It is your responsibility to learn!

OK so let’s begin already!

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.

How can we think about Energy?

… Let’s Use a Model!

ModelsUseful way to think of and address questions

about phenomena(e.g. Ideal gas model)

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

(This should be familiar from Chemistry)

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

Next lecture is Wednesday

Quiz 2 will cover today’s lecture, and Discussion/Lab 1 material INCLUDING

FNT (For Next Time) questions.