40. Heat Engines

A thermoelectric device which runs a propeller has two legs. The device will run if one leg is in a hot cup of water and the other in a cold cup of water, but not if both legs are in the same cup of water. (The hot and cold water can be mixed for the second step to show that the ability to do work has been lost.)

The "Thermobile" will spin (by shape-memory retention) if one end is dipped in hot water. Air at room temperature serves as the other reservoir (also see Laws of Thermodynamics).