Announcements 9/5/12 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

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 thermometerc. triple point of waterd. ideal gas law

Other comments?–

Airplane Wings

Principle 1: deflection

Principle 2: Bernoulli

http://www.av8n.com/how/htm/airfoils.html

“airfoils”

Curve balls

Ball moving to the right (i.e. air moving to the left), with topspin

Ping pong demo!

Worked Problem:faucet

Pmain 3mr2

r1

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: 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.

a.

b.

c.

d.

0

0

0

0

Abs. 0 Room T

Demos: “What’s a thermometer?”

Liquid bulb thermometer Constant volume thermometer

Thermal contact Two objects in “thermal contact” will come

to “thermal equilibrium”, and then have the same “temperature”.

What is thermal contact?

What is thermal equilibrium?

What is temperature?a. Is there a maximum temperature?b. Is there a minimum temperature?

Thermal expansion

What went wrong here?

Thermal Expansion

The equation:

= “________________”

0L L T

For reference: steel = 11 10-6 /C

From warmup

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

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:

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:

Demo: Ring & Ball Demo: Bimetallic strip Video: Bimetallic strip

Clicker question:

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 degreeb. 210-5 per degreec. 10-10 per degree

Area & Volume Expansion (of solids)

The equations:

0?V V T

= …

0?A A T

Clicker question:

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 heliumb. jar of neonc. same number

Ideal Gas Law

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:

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?

Quick Writing

Important stuff: P must be in _______V must be in _______T must be in _______n = ________R = ________N = ________kB = ________

What’s a mole?How are R and kB related?

Units of PV?

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

Ideal Gases:

Video: “Barrel crush”

Image from Wikipedia: http://en.wikipedia.org/wiki/Atmospheric_pressure

Bottle sealed at 14,000 feet

Picture at 9,000 feet

Picture at 1,000 feet

Demos/Videos:

Demos: Liquid nitrogen!a. Two balloonsb. Rubber nailc. “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