Transcript Welcome to Physics 7A!

Welcome to Physics 7A!
Lecturer: Cassandra Paul
Slides 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
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Select Class:
Scroll down in ‘Setup Menu’ until you see ‘ID’
Press the Green Arrow
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Test Clickers
• Have you had Physics before?
A.
B.
C.
D.
E.
No, None
Conceptual Physics Class (HS or College)
Algebra Based High School Class
Algebra Based College Course
Calculus Based College Course
What do you think of when you hear
the word Physics?
Can ice be colder than 0°C?
Why is the sky blue?
What is physics?
We begin with the child-like wonder about our everyday world.
How does a light switch work?
How do magnets work?
Why does she start spinning
so much faster when she
pulls her arms and legs in?
Why do planets orbit?
What is “rainbow” really?
As Physicists we...
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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: Energy
What 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 Energy
Conservation of Energy
Energy 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!
Models
Useful way to think of and address questions about
phenomena
(e.g. Ideal gas model)
Models in Physics 7A
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.
• 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 with
These two…
Three Phase Model of Matter
(This should be familiar from Chemistry)
Three-Phase model of Matter
Example H2O
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•
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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.
Three-Phase model of Matter
Example H2O
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.
Three-Phase model of Matter
Temperature
gas
l-g coexist
TBP
s-l coexist
liquid
TMP
solid
Energy added or removed
Example: Melting ice initially at 10C, and bringing it to 15C
Temperature
Final
gas
Initial
TBP
liquid
T
TMP
solid
T
T const
Energy added
Energy Interaction Diagrams
Based on the energy interaction model, it shows you
how energy is transferred, how energy is conserved
between energy systems.
Energy-Interaction Model
Energy systems:
There are many different types of energies called energy
systems:
Emovement
(KE)
Etherma
Esprin
Ebond
g
l
Eelectri
Egravit
c
y
........
For each energy system, there is an indicator that tells us how
that energy system can change.
Ethermal: indicator is temperature
Ebond: indicator is the initial and final phases
Energy interaction diagrams - closed
Ea
Eb
Ec

Conservation
of Energy
The total energy of a closed physical system must remain
constant. In other words, the change of the energies of all
energy systems associated with the physical system must
sum to zero.
Change in system energy = ∆Ea + ∆ Eb + ∆ Ec = 0
Energy interaction diagrams - open
Ea
Energy added
Eb

Ec
Energy removed
Conservation of Energy
The 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
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
System: H2O
Initial: Solid (Ice) at -10°C
Final: Liquid (Water) at 15°C

HEAT
Ice
Etherm 
How can we model how much Energy is
needed to melt ice initially at -10C, and
bring it to 15C?
Mixed Water

Ebond
TT
ml
I: T=-10°C
F: T=0°C
I: all solid
F: all liquid
al
+
+
Etherm 
al
T
I: T=0°C
F: T=15°C
+
+
ΔEths + ΔEbond + ΔEthl = Q
Condensing Steam initially at 100°C
to a final temperature of 40°C
Temperature
Initial
Final
TBP
TMP
Energy added or removed
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
System: H2O
Initial: Gas (steam) at 100°C
Final: Liquid (Water) at 40°C

I: T=100°C
F: T=40°C
Ebond
mg

T

al
HEAT

Etherm
Water

Mixed
I: all gas
F: all liquid
ΔEthl + ΔEbond = Q
Next lecture is Wednesday
Quiz 2 will cover today’s lecture, and
Discussion/Lab 1 material INCLUDING
FNT (For Next Time) questions.