- the random motion of [[Atom|Atoms]] - Feynman says the "jiggling" of them - is specifically the [[Kinetic Energy]] of [[Molecule|Molecules]] - heat can be transferred by: - [[Conduction]] - touching the thing - [[Infrared|Infrared Radiation]] - filament of light bulb, lights up near your hand - (but not touching) - air is very poor conductor, so only way heat comes is the radiation through distance - [[Buoyancy]] - most common example is boiling water - if you put hand over boiling water, it'll feel hot - bouyant water is rising up spreading the heat to you, then circling back down - process is called [[Convection]]