Key and Matchbook Windlass
Purpose
A matchbook and keys hang on opposite ends of a string draped over a horizontal rod. When released, the keys fall while the matchbook swings like a pendulum, wrapping the string around the rod. The increasing friction (capstan effect) eventually stops the keys mid-fall.
Figure 1:
Initial setup: hold the matchbook horizontally while the keys hang vertically. The rod extends over the edge of the bench toward the audience.
Figure 2:
Just after release: the matchbook swings in a wide arc as the keys fall, beginning to wrap the string around the rod.
Figure 3:
Mid-motion: the matchbook spins faster as its radius shortens. Multiple string wraps are building up friction on the rod.
Figure 4:
Final state: the string has wrapped enough times around the rod that friction balances the weight of the keys, stopping their fall.