Why Do Figure Skaters Spin Faster when They Pull Their Arms In?
distance, so cutting the distance in half decreases the moment of inertia by a factor of four. If the moment of inertia decreases but the angular momentum stays constant, the rate of rotation must increase. As the skater brings her arms in, she spins faster and faster, going from about 2 rotations per second to 10 or more rotations per second. The conservation of angular momentum also explains why Earth spins on its axis. According to one theory, the solar system formed from a large cloud of cosmic dust which was spinning in space. Parts of the cloud were pulled together by gravity, forming pockets of greater density which pulled even more matter inward. These clumps of matter eventually formed the sun and the planets. As the rotating material pulled closer and closer together, the total angular momentum was conserved. A large, slowly rotating cloud of matter spread out across vast areas of space became a small number of rapidly spinning balls of dense matter.
