Announcements 9/7/11
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Prayer
Small change to HW policy – see email
Class directory
New student who talked to me yesterday: please
see me (I’ve forgotten your name, my apologies)
(1+x)n ≈ 1 + nx
Frank & Ernest
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. Fahrenheit and Pentatonic
d. Kelvin and Celsius
e. Kelvin and BTU
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
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
Videos/Demo:
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Demo: Ring & Ball
Demo: Bimetallic strip
Video: Bimetallic strip
Thought question (ungraded):
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If the expansion of all of the linear
dimensions of an object is by a factor of 10-5
per degree, what should be the expansion
factor of the surface area of the object?
a. 10-5 per degree
b. 210-5 per degree
c. 10-10 per degree
Area & Volume Expansion (of solids)
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The equations:
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 as P increases V will decrease
Hold P constant, then as T increases V will increase
Hold P, T, constant, then as #molecules increases V
will increase
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 _______
Units of PV?
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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Image from Wikipedia:
http://en.wikipedia.org/wiki/Atmospheric_pressure
Bottle sealed
at 14,000 feet
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Picture at
9,000 feet
Video: “Barrel crush”
Picture at
1,000 feet
Demos/Videos:
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Demos: Liquid nitrogen!
a. Two balloons
b. Rubber nail
c. “Balloon pop”
d. “Nitrogen Tower”
Calculation (if time): How much volume will 1
liter of liquid nitrogen fill when it becomes gas?
 Density of LN = 0.807 g/cm3
 Molar mass of N2 = 28 g/mol
 Temperature in this room = 70 F
 Atmospheric pressure in Provo today? 0.85 atm
Answer: 821 L