Description:A set of about 20 small steel balls of equal mass models the air. The balls are set into motion by vibration of the walls with the device tilted. A moveable bar positioned in the device is pushed upward by collisions with the balls. As the vibration rate of the walls is raised, raising the temperature and thus increasing the average molecular speed, the bar is pushed further upward, representing increased volume at a constant pressure (the weight of the bar). Use of a 140 Volt Variac extends the temperature range upward to make the trend more clear.