Suicide Pendulum

WARNING: The bowling ball is heavy and can cause serious bodily harm. Release, DO NOT PUSH, the bowling ball away from your face. Note that it is difficult not to flinch when the ball swings towards your face. Practice this demo in advance and perform with extreme caution!

Equipment: A bowling ball suspended from the ceiling on a cable.

What it does: The bowling ball pendulum is held up to the demonstrator's face and is released. Because of conservation of energy, the ball will not swing higher than the height at which it was released (in fact, because energy is lost during the swing, the ball falls slightly short of the demonstrator's face when it completes one full period). To paraphrase Leigh, physicists believe in conservation of energy and therefore have complete confidence that if they release the ball right next to their head that the ball will swing back and stop, not continue on and smash their head. The apparent danger of having one's head smashed gives the demonstration great crowd appeal. The demonstration usually draws an audible response from the audience.

Concepts Demonstrated: Conservation of energy, demonstrated in a very dramatic manner.

Classroom assembly:

• Keeping the cable taught, pull the pendulum (bowling ball) to one side until it touches your nose. Be sure to stand straight and still.
• Release the pendulum, taking care not to move your face.
• Remain very still while the pendulum swings through one full period.

WARNING: The bowling ball is heavy and can cause serious bodily harm. Release, DO NOT PUSH, the bowling ball away from your face. Note that it is difficult not to flinch when the ball swings towards your face. Practice this demo in advance and perform with extreme caution! Care must be taken not to hit benches and other objects with the pendulum.

Setup Time: Setup time during the lecture is short. Setup time before the lecture is long (note: this setup is usually done by a technician).

Difficulty: Straightforward after practice. Setup before the lecture is somewhat involved and requires the help of a technician.

Visibility: High. This demonstration is appropriate for large lecture halls.

Related demonstrations:

References: PIRA 1D50.40

Original Construction: An eye hook was screwed into a bowling ball. The bowling ball was suspended from the ceiling by a steel cable.