Announcements 1/12/10
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Prayer
Extra-credit lecture, “The Physics of Bicycles”, right after
class today, 2 pm, 455 MARB. If you attend, turn in 1page (max) summary to get extra credit points.
I won’t have office hours today.
For HW problem 4-9 (extra credit), you need the bulk
modulus of copper. You should get that from Chapter 12
of your book (if you don’t have that chapter, there are
some books available in the Tutorial Lab).
I’m not following books order for Chapters 20-22. Be sure
to look at syllabus.
Don’t forget to turn in work for ALL homework problems
(1+x)n ≈ 1 + nx
Reading quiz (graded):
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Which two temperature scales have the same
sized intervals, varying only in their choice of
the zero point?
a. Fahrenheit and Celsius
b. Fahrenheit and Kelvin
c. Kelvin and Celsius
d. Kelvin and BTU
e. Fahrenheit and Pentatonic
Temperature
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Temperature scales
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What’s a thermometer?
Demos:
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Liquid bulb thermometer
Constant volume thermometer
Thermal contact
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Two objects in “thermal contact” will come to
“thermal equilibrium”, and then have the same
“temperature”.
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What is thermal contact?
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What is thermal equilibrium?
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What is temperature?
a. Is there a maximum temperature?
b. Is there a minimum temperature?
Thermal expansion
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What went wrong here?
Thermal Expansion
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The equation:
L  a L0T
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a = “________________”
For reference: asteel = 11  10-6 /C
Videos/Demo:
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Demo: Ring & Ball
Demo: Bimetallic strip
Video: Bimetallic strip
Thought question (ungraded)
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You heat a disc with a hole in
it. Will the radius of the hole
get larger, smaller, or stay
the same?
a. Larger
b. Smaller
c. Stay the same
Thought question (ungraded):
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If the expansion of all of the linear
dimensions of an object is proportional to ΔT,
what should the expansion of the surface
area of the object be proportional to?
a. ΔT
b. 2ΔT
c. ΔT2
d. The surface area won’t change with
temperature.
e. None of the above
Area & Volume Expansion (of solids)
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The equations:
A   A0 T
V   V0 T
=…
 =…
Thought question (ungraded):
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Two jars of gas: helium and neon. Both have
the same volume, same pressure, same
temperature. Which jar contains the greatest
number of gas molecules? (The mass of a neon
molecule is greater than the mass of a helium
molecule.)
a. jar of helium
b. jar of neon
c. same number
Ideal Gas Law
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Hold T constant, then V decreases as P
increases
Hold P constant, then V increases as T
increases
Hold P, T, constant, then V increases as
#molecules increases
Summary:
Quick Writing
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Ralph is confused…the book calls two different
equations “the ideal gas law”: “PV = nRT”, and
“PV = NkBT”. Why are they both called the
ideal gas law, when only the first equation
looks like what he learned in chemistry?
Important stuff:
P must be in _______
V must be in _______
T must be in _______
n = ________
R = ________
What’s a mole?
N = ________
How are R and kB related?
kB = ________
Ideal Gases:
Molecules collide like superballs (elastic) due to
repulsive forces
 No attractive forces
 Never condense into liquids or solids
 Are like “frictionless surfaces”, “massless
pulleys”, fluids without viscosity, projectiles
without air resistance, etc.
 That is, they don’t really exist, but are useful
constructs
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Demos/Videos:
Video: “barrel crush”
 Demos: More liquid nitrogen!
a. Two balloons
b. Rubber nail
c. “Balloon pop”
d. Expansion ratio
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