Welcome to Physics 7A!

Winter 2011

Welcome to Physics 7A!

Winter 2011

Prof. Robin D. Erbacher343 Phy/Geo Bldg

erbacher@physics.ucdavis.edu

Prof. Robin D. Erbacher343 Phy/Geo Bldg

erbacher@physics.ucdavis.edu

This course has two instructors: Prof. Robin Erbacher (me) rderbacher @ucdavis Prof. Hsin-Chia Cheng (Lead DL Instructor) hcheng @ucdavis

You are enrolled in Physics 7A-A/B, lectures Mondays. 7A-C/D is offered this quarter as well but has different meeting

times.

Final exam is Saturday March 19th, 10:30 am-12:30 pm If you know you cannot make the final, you should take 7A in

a different quarter. There are *no* make-up exams.

This course has two instructors: Prof. Robin Erbacher (me) rderbacher @ucdavis Prof. Hsin-Chia Cheng (Lead DL Instructor) hcheng @ucdavis

You are enrolled in Physics 7A-A/B, lectures Mondays. 7A-C/D is offered this quarter as well but has different meeting

times.

Final exam is Saturday March 19th, 10:30 am-12:30 pm If you know you cannot make the final, you should take 7A in

a different quarter. There are *no* make-up exams.

Our website will be centered around Smartsite.

Please read the course policy as soon as possible and let us know if you have questions.

Cheating of any sort is not tolerated. This includes but is not limited to:• Copying during quizzes/exams.• Taking a test for another student.• Having a friend use your clicker to register you as present when you are not.• Modifying a quiz before asking for a re-grade.

As soon as dishonesty is suspected the student is referred to Student Judicial Affairs.

A.K.A - Clickers!

We will use these to allow you (and us) to gauge your understanding on conceptual questions during lecture.

You will receive credit for participation by answering questions. No matter whether correct or wrong.

You need your own with your own student ID (bookstore).Bring clicker to next lecture!

• We will have 5 quizzes during lectures, on alternate weeks.

• You must attend your assigned lecture time: sleeping is not an excuse to go to a different lecture.

• Your first quiz will be next week, Monday Jan 10th. Bring a calculator -- you may need it and we don’t have any to lend.

QRST

Green circles help identify you (name, ID).Purple circles helps them enter results accurately.We use letter “rubric” codes for partial credit scoring.

The full course policy is in the document linked on Smartsite under Resources. You must read this!

Quizzes: The lowest of your 5 quiz scores will be dropped for the final quiz average. There are no make-up quizzes. If you miss one, that one will be dropped.

Final Grade Determination

Your final grade is calculated two ways: 5% PRS + 45% top 4 quiz avg + 50% final exam +/- DL

OR5% PRS + 20% top 4 quiz avg + 75% final exam +/- DLThe most favorable score is used for your grade.

Discussion Labs (DLs) begin immediately after lecture today with section 1. All DLs are in EPhSci 2319. Equipment tables are set up there.

People who are wait-listed or not enrolled in the DL need to obtain a PTA number from their TA:

• In DL: Don’t join a table immediately.• Collect in a corner while the TA begins business,• Then the TA will address enrollment issues.• Full sections will give PTA numbers at the 2nd meeting.

Important

I’m an Associate Professor of Physics (tenured) here at Davis. My research is in elementary particle physics.

• I’m from Pacifica, CA (well, Los Angeles originally)

• I went to U.C. San Diego for undergraduate, majoring in physics, with minors in Lit/Writing and Poly Sci.

• I went to graduate school at Stanford University. PhD thesis at SLAC (Stanford Linear Accelerator Center). “Precision Measurement of the Spin Structure of the Proton”

• Postdoctoral Research Associate at Fermilab (Fermi National Accelerator Lab) in Chicago suburbs.

• Professor: UC Davis Physics department.

protons anti-protons

+

Fermilab (Tevatron): (Fermi National Accelerator Lab), near Chicago.

CERN (LHC): (Conseil européen pour la Recherche Nucléaire)

Fermilab

We begin with the child-like wonder about our everyday world.• Why is the sky blue?• Is there anything colder than ice?• How does a light switch work?• How do magnets work? • How do planes fly?• Why does scuffing your feet on carpet “zap” you?• Why can some people play pool with great precision?

Some of these models use the same principles: Depends on the question asked!

How do we know that MEarth = 5.98 x 1024 kg?

“Look it up in a book” misses the point.

Treat the Earth, planets, and the sun as systems that obey the same principles (or models) as mundane objects such as apples and blocks.

Using similar principles and models we can measure the mass of stars and galaxies:

• We know how much stars weigh (roughly).• We know how much light stars give off (roughly).• … So we can “count” the stars and figure out how much of the mass is “stuff we know”.

But “stuff we know” is only ~<3% of the mass of the galaxy!

Lots of discoveries to make!

•Wonder about the world around them.•Try to explain phenomena using a few principles (models).•We cannot “pick and choose” when an explanation works

What is the world made of?What holds the world together?

Where did we come from?

•While our models may not always hold true, we have some understanding of when they’re valid.

Physics is taking this approach in the physical world!

Physics 7 is a 3-quarter series of physics classes, typically taken by bio-science and other non-physical 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.

Physics 7 is a new approach to teaching and learning introductory physics. It involves:

• Learning by doing. • Active learning.

• Application of models to various physical systems.

• Learning by exploration in a small group.

• Using a chalkboard and discussing openly.

It will require your active participation! Your DL grade will reflect this.

Models…Discussion/Lab

LectureQuiz & Final Text

Active learning is key to “getting” the concepts in Physics 7 and being able to apply them to new situations.

• Most of your learning will take place in the Discussion Labs (DLs), so attendance is mandatory.

• The lecture will provide a framework (and in some cases a review) for the subject material, and will allow more explanation and demonstration of concepts.

• Your DL instructor will only give you guidance and pointers about the right way of thinking-- they will not in general solve the problems for you!

• To solve the problems, interact strongly with your small student group (5-6 people) and the DL section (the whole class: ~30 people).

We do not emphasize getting the right answer, though that is important too.

In DLs, FNTs (For Next Times), quizzes, and the final, we are looking for indications that:

1) The problem is clear to you.

2) You are arriving logically to the next step.

3) You clearly understand which model to apply to the problem at hand, why, and how to do it.

• Learn to think logically and to make valid arguments when describing a system or solving a problem.

• Learn to apply analytical principles and logic to understand problems and devise solutions.

• Learn to reason with models and explain the world around us.

We are not here to memorize equations or rote procedures in problem-solving.

ModelsModels

“The atom is nothing but a little electron orbiting around a proton.”

Models in Physics:• Newtonian mechanics• Standard Model of particle physics• Standard Model of cosmology

Models in Biology:• Protein-lipid interaction model• Protein-protein interaction model

(Don’t ask me about these last two!)

• 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…

Intro:Three Phase Model

Intro:Three Phase Model

The basic idea

Stage A: This is the very cold ice starting to warm up Here, it goes from -30 to 0. It is all still ice. Energy is added, but no phase change.

Stage B: Ice is now at zero degrees and heat (energy) is still being added. As energy is added, the temperature is constant and stays at zero until all ice is gone. Solid/liquid co-exist. All the energy went into melting the ice, not changing temperature.

Stage C: It is now all water and heat (energy) is still being added. The heat goes into raising the temperature of the water. No phase change.

Stage D: The water is now at the boiling point (100 deg) and heat is still being added. The energy goes into changing the water into steam. No temperature change. This is another mixed phase. Liquid/Gas co-exist.

Stage E: All of the water has now turned into steam. As heat is added, the temperature increases. No energy goes into changing phase, all into making the pure substance hotter.

Intro:Energy Interaction

Model

Intro:Energy Interaction

Model

Etherma

l

EbondEmovement

(KE)

Egravit

y

Eelectri

c

Esprin

g

There are many different types of energies called energy systems:

........

For each energy system, there is an indicator that tells us how that energy system can change:

Ethermal: indicator is temperatureEbond: indicator is the (mass of) initial and final phases

Ea Eb Ec

Conservation of EnergyThe total energy of a closed physical system must remain constant. So, the change of the energies of all energy systems associated with the physical system must sum to zero.

Change in closed system energy = ∆Ea + ∆ Eb + ∆ Ec = 0

Ea Eb Ec

Conservation of EnergyThe change of the energies of all systems associated with an open physical system must sum to the net energy added or removed. Energy is added or removed as Heat (Q) or Work (W).

Change in open system energy = ∆Ea + ∆ Eb + ∆ Ec

= (Energy added) - (Energy removed) = Q + W.

Energy added Energy removed

Example: Melting IceTi= 0°C Tf = room temperature

Tem

pera

ture

Energy of substance

solid

liquid

gas

l-g coexist

s-l coexist

Initial

TMP

TBP

Final

Example: Melting IceProcess 1: Ice at T=0ºC Water at T=0ºC

Process 2: Water at T=0ºC Water at room temperatureTem

pera

ture

Energy of substance

solid

liquid

gas

l-g coexist

s-l coexist

Process 1Initial

TMP

TBP

Process 1Final /

Process 2Initial

Process 2Final

Example: Melting IceProcess 1: Ice at T=0ºC Water at T=0ºC

Ice

Initial phase Solid, Final phase Liquid

Etherm

al

Ebond

Example: Melting IceProcess 1: Ice at T=0ºC Water at T=0ºC

Ice

∆T=0

∆Eth=0

Initial phase Solid, Final phase Liquid

Etherm

al

EbondHeat

Example: Melting IceProcess 1: Ice at T=0ºC Water at T=0ºC

Ice

∆T=0

∆Eth=0

Initial phase Solid, Final phase Liquid

∆Eth + ∆Ebond= Q+W

∆Ebond= Q

Etherm

alEbond

Heat mwater

Ice

Etherm

alEbond

Example: Melting IceProcess 2: Water at T=0ºC Water at room temperature

Initial phase Liquid, Final phase Liquid

Ice

Etherm

al

Ebond

Example: Melting IceProcess 2: Water at T=0ºC Water at room temperature

Initial phase Liquid, Final phase Liquid

∆Ebond= 0

T

∆Eth + ∆Ebond= Q+W

∆Eth= Q

Heat

Thermal Equilibriumand Heat

Thermal Equilibriumand Heat

An ice-cube at 0oC sits in a bath of water at 0oC. Water and ice can exchange heat with each other

but not with the environment.What is the direction of heat transfer?

A. From ice-cube to waterB. From water to ice-cubeC. Neither of aboveD. Impossible to tell

00 CWater

Ice-cube00 C

Starting definition of heat (to be revised much later):

Heat (Q) is the transfer of energy from a hot object to a cold object because the objects are at different temps.

Energy leaves hot objects in the form of heat.Energy enters cold objects in the form of heat.

Corollary: If the two objects are at the same temperature, no Q (heat) flows between them.

Low temp High tempQ

If the two objects are at the same temperature, no heat flows between them.

A system in thermal equilibriumin thermal equilibriumis a system whose temperature is not changing in time.

Tfinal

Energy leaves hot objects in the form of heat Energy enters cold objects in the form of heat

Low temp High temp

The Zeroth law of thermodynamics says:

Since they are in thermal equilibrium with each other, there is no net energy exchanged among them.

If objects A and B are separately in thermal

equilibrium with a third object C, then A and B

are in thermal equilibrium with each other

If objects A and B are separately in thermal

equilibrium with a third object C, then A and B

are in thermal equilibrium with each other

The Zeroth law of thermodynamics example:

• Let the third object C be the thermometer.• If the two readings are the same, then A and B are also in thermal equilibrium.

• Energy (heat) will not flow between A and B if put together.

A cup of hot coffee left in a room…

A thermometer

Cold beer

It can take some time for things to reach thermal equilibrium with its environment. ~ what is happening at microscopic level? => more to

come when we cover Particle models of thermal energy

C =

[C] = J/K

Coffee cup: ceramic material

A thermometerTip: metalBody: glass, plastic

Beer glass:glass

Heat capacity [C] of substances:A measure of the amount of energy required to

increase the temperature of the substance a certain amount

€

QΔT

Heat capacity C is an extensive property:2kg of water will have twice the heat capacity of 1kg water

Heat capacity of substances:A measure of the amount of energy required to

increase the temperature of the substance a certain amount

C =

[C] = J/K

€

QΔT

Porcelain 1.1kJ/kgK

Tip:metal

(Silver: 0.24kJ/kgK) Body: plastic~ 1.2kJ/kgK

Glass 0.84kJ/kgK

Specific heat capacity Cp is an intensive property:Specific heat capacity only depends on the substance

Specific heat capacity Cp of substances:the amount of energy per unit mass/unit mole required to

increase the temperature of the substance by one degree Kelvin

[Cp] = kJ/kgK = kJ/moleK

The scientific "calorie" is spelled with a lower-case "c".

One "calorie" = 4.184 Joules

The "dieter's" calorie is spelled with an upper-case "C".

One "Calorie" = 1000 calories

Next Time: Energy Conservation,more on Equilibrium,Heat Capacity, Specific

Heat, More Energy Interaction Diagrams

Next Time: Energy Conservation,more on Equilibrium,Heat Capacity, Specific

Heat, More Energy Interaction Diagrams

Next lecture contains a quiz.

Bring your calculator.

Bring your Clicker for participation credit.

Background Information:Background Information:

• Models can help us organize our thinking, can contain other models, and can be very useful.• Models also have limitations: experiment is the final judge.

Pure substances: one chemical substance -water vs. unpasteurized apple cider

Phases: solid, liquid, and gas

Temperature: measure of the hotness of something

Energy: here, it is something that is transferred in the form of heat or work

Phase change temperature: the unique temperature at which a pure substance changes from one phase to another

• Energy is both a thing (quantity) and a process. You & I contain energy, as do the chairs you sit on and the air we breathe. • We cannot see it, but we can measure the transformation of energy (or change, ΔE).

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.

NOTE: The total energy of a closed system remains constant!This course is about energy, how its transferred, how its conserved.