Suspended Collision Balls
To demonstrate the conservation of momentum and energy.
Suspended balls apparatus
Conservation of momentum can be demonstrated simply by pulling various numbers of balls back from equilibrium and allowing them to swing back towards equilibrium. Momentum conservation is demonstrated by the fact that the number of balls that collide with the set of resting balls determines the number of balls that are knocked off the other side of the stack. That is, since the balls all have the same mass and the collisions are nearly elastic, the only way to conserve momentum and energy is to have the same number of balls (amount of mass) at the same velocity leave the collision as enter it.
The balls on the apparatus have a tendency to slide so some adjusting of their positioning may be necessary before the demonstration. Also there is some space between some of the balls, which also hinders the length of the demonstration, as there is more loss of motion then usual.