Chapter 2: Atoms and HeatHeat is the kinetic energy of

motion of the atoms or molecules in an object

Temperature is a measure of the average kinetic energy per atom or per molecule

In general, light atoms move faster than heavier atoms at the same temperature

Remember: heat is just energy

0th Law and temperature Two objects in thermal contact will

eventually reach the same temperature This is how thermometers work.Fahrenheit, Celsius, Absolute (Kelvin)T(K) = T(C) + 273Go between T(C) and T(F) with

Google, calculator, or look it up.32 F, 212 F 0 C, 100 CLiquid N2 77 K or -196 C or -321 F

Thermal e x p a n s i o nL = L0 T

is thermal expansion coefficientCan write a similar expression for volume

change. How bulb thermometers work.Expansion joints in highways and bridgesConcorde is almost a foot longer in flightBi-metallic thermal switch

Water is a special case

Water contracts as it cools, until it reaches 4 ˚C, then it expands until it freezes.

So water that’s about to freeze is lighter than water at 4 ˚C, so lake freezes from the top down, rather than the bottom up.

Boiling and the Leidenfrost effectDrop water on griddle. The drops dance

when the griddle is hot enough.Hot griddle makes thin layer of steam out of

the bottom part of the drop.Steam layer doesn’t transfer heat well,

which insulates the drop from the heat of the griddle.

Works for other liquids also -- LN2

Why does the quarter boil twice?

Heat engines and efficiencyQH = W + QC

Energy In = Energy OutQC ≠ 0

TH

TC

Engine

QH

QC

WThere is a game.But you can’t win.You can’t even break even.And you can’t quit.