Keywhip

Purpose

Demonstrate angular momentum conservation in a surprising way.

Equipment

String with keys on one end and a matchbox on the other end.

Images

d3-32

Description

A string about one meter long has a (relatively heavy) set of keys on one end and a (very light) match box on the other end. The string passes over a pencil with the keys hanging down and the matchbox held horizontal to the pencil with about two/thirds of the string between the pencil and the matchbox. Q: What will happen when the match box is released?A: Surprisingly, the keys will not fall to the floor. When the matchbox falls it develops angular momentum. Conservation of angular momentum of the matchbox causes it to rotate very rapidly about the pencil as the string pulls it in. Before the