Falling Little Balls

If we leave two balls fall together and from the same height, they will rebound almost up to the same height. Anyway, something strange happens if we put the lighter little ball (a ping pong one) over the heaviest (of caoutchouc). The ball that was over squirts to the ceiling.

In the instant of fall on the ground a hidden collision occurs: the bigger ball rebounds on the ground and changes the direction of the velocity vector before the smaller one, which continues to go toward the ground. Due to the elastic collision the quantity of motion of the heavier ball is transmitted to the lighter ball and therefore this latter one rebounds to a major height.

Once again we convince ourselves that we must not believe in illusions. The behaviour of the balls don't contradict principles of conservation in physics.