Announcements 9/5/12
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Prayer
Please introduce yourself to 4 people sitting near
you before class
Anyone need a class directory?
(1+x)n ≈ 1 + nx
Frank & Ernest
From warmup
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Extra time on?
a. When we make the simplifying assumption when
deriving that ß=3a, why can we eliminate some of
the terms but not all of them?
b. constant-volume gas thermometer
c. triple point of water
d. ideal gas law
Other comments?
–
Airplane Wings
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Principle 1: deflection
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Principle 2: Bernoulli
“airfoils”
http://www.av8n.com/how/htm/airfoils.html
Curve balls
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Ball moving to the right (i.e. air moving to the
left), with topspin
 Ping pong demo!
Worked Problem:
faucet
r2
Pmain
3m
r1
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The faucet of radius r2 = 2 cm puts water out at
15 liters/minute. The pressure at the opening of
the faucet is about 1 atm. The water main (r1 = 6
cm) is 3 m below the faucet.
a. What is the speed of the water in the narrow
pipe?
b. What is the pressure in the main?
Answers: 0.199 m/s; 1.307E5 Pa = 1.290 atm
Clicker question:
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The following represent the Celsius, Fahrenheit,
Kelvin, and Rankine scales. (Rankine is like Kelvin,
but for F instead of for C.) Which corresponds to
the Celsius scale? Each tick mark = 20 deg.
Abs. 0
Room T
a. 0
b.
0
c.
0
d.
0
Demos: “What’s a thermometer?”
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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
From warmup
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To make a very sensitive glass thermometer,
which liquid would be the best choice:
mercury, alcohol, gasoline, glycerin, or
water?
a. Gasoline. It has the highest volume
expansion coefficient of mercury, alcohol,
gasoline, and glycerin; and, it has a larger
range of temperatures at which it is a liquid
than water.
From warmup
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Two spheres are the same size and are made of
the same material, but one is solid and the
other is hollow. Which expands more when the
temperature is increased? Explain.
a. Both spheres expand the same amount, as a
cavity within an object expands in the same
way as if it were filled with the same material
that the object is made of.
From warmup:
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At room temperature, the sphere just barely fits
through the ring. (A) After the sphere is heated, it
cannot be passed through the ring. Explain. (B)
What if the ring is heated…can the sphere pass
through? Explain.
(A) The metal of the sphere has expanded and no
longer fits through the ring.
(B) The sphere will be able to pass through more easily
than originally because the ring has expanded,
including the hole in the ring.
Videos/Demo:
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Demo: Ring & Ball
Demo: Bimetallic strip
Video: Bimetallic strip
Clicker question:
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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:
A  ? A0 T
V  ? V0 T
b=…
Clicker question:
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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
 Don’t 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