The ball bearings represent gas particles and are fired around by a motor-driven plate bouncing a piece of rubber glove up and down. The ball bearings move at varying speeds. It would be interesting to see a Maxwell-Boltzmann type curve for them. In a gas, the average velocity is zero because there are as many negative velocities as positive. So we have to use root mean square (rms) as a sensible average. Each molecule hits the polystyrene at the top. There is an impulse force. This keeps the polystyrene up. Unlike ideal gases, the collisions involving the ball bearings cannot be elastic.
