PURPOSE: To demonstrate conservation of angular momentum.

DESCRIPTION: A subject, holding the weights with his or her arms extended, is started into rotation. When the weights are pulled inward to the chest of the subject, the moment of inertia of the system is decreased, leading to significant increase in the angular speed of the rotating chair. An aerial view of this action can be seen operating in either the clockwise or counterclockwise directions.

SUGGESTIONS: This can produce a significant increase in rotational speed; BE CAREFUL. See Question of the Week #311 for information on using this demonstration to enhance class involvement. See also Question of the Week #308 for a classroom question involving use of a single weight to create a large stable rotation of your body from a number of short rotations.

REFERENCES: (PIRA 1Q40.10)

EQUIPMENT: Rotating chair with weights.

SETUP TIME: None.