Announcements 9/7/11 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):

Which two temperature scales have the same sized intervals, varying only in their choice of the zero point?

a. Fahrenheit and Celsiusb. Fahrenheit and Kelvinc. Fahrenheit and Pentatonic d. Kelvin and Celsiuse. Kelvin and BTU

Temperature

Temperature scales

What’s a thermometer?

Demos:

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

Thought question (ungraded)

You heat a disc with a hole in it. Will the radius of the hole get larger, smaller, or stay the same?

a. Largerb. Smallerc. Stay the same

Videos/Demo:

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

Thought question (ungraded):

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:

0V V T

= …

Thought question (ungraded):

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 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

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