Theory: The average speed of molecules in a gas increases with temperature. Also, at constant pressure, volume expands as temperature is increased. This model illustrates both of those principles.
Description: The function generator should be set to sine output, and a frequency of about 50 Hz. The amplitude is analogous to temperature: increasing the amplitude gives the ball bearings more energy, which results in them occupying more space; decreasing the amplitude does the reverse.
Setup time: 5 minutes.