Pull one of the balls away and then let it go and watch what happens. Gradually increase the number of balls you pull away (make sure they keep touching) and repeat the experiment.
How does it work
After the balls strikes the remaining ones, the same number of them springs away from the other side. This follows from the law of conservation of momentum and energy. The stationary steel balls only pass those abstract properties on by means of a longitudinal wave travelling in steel.
The name ‘Newton’s cradle’ was coined by Simon Prebble, an English actor, who in 1967 put the previously known set of bouncing balls on the market as a toy.