Newton’s cradle

HOW

1. Move one ball to the side, then release it and observe the collision.
2. Increase the number of moved balls one by one (make sure they are in contact with each other).
3. Repeat the experiment and observe what changes.

WHY

When you release the balls, an equal number of them always bounce off the other side. This is a result of the law of conservation of linear momentum and energy. Immobile balls are merely transmitters of these quantities. This takes place through a longitudinal wave propagating through the steel balls.