Fun with a pendulum
Suspend a hard ball about 8 cm in diameter on a cord over a table. The cord should be at least 1.5 m in length and should be just high sufficient off the table to hit the top of a pencil which has been placed in cotton reel and rests on the table. Pull the pendulum and release it in like a way that it misses the pencil on the outward swing and knocks it over on the backward swing. You will search that it needs a great deal of practice to become skilful at this.