PURPOSE: To illustrate how a rigid rod topples on a frictionless surface.

DESCRIPTION: A wooden dowel with its center of mass marked is held vertically with the bottom end supported by a very light air table puck. When it is released and allowed to topple, which point of the stick will be directly above the original support point: the top end, the bottom end, or the center of mass? Note that the stick has a small counterweight on its top end to compensate for the mass of the puck. Click your mouse on the photograph for an mpeg video.

SUGGESTIONS: Let your students guess before doing the experiment.

The air table is only available in rooms 1410, 1412, and 0405 because it will not fit through a standard door.

See Question of the Week #53 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA unknown.)

EQUIPMENT: Pointer with counterweight, air table with puck, as photographed.

SETUP TIME: 10 min.