PURPOSE: To encourage thought about the motion of a pendulum and related forces.

DESCRIPTION: A simple pendulum bob is released from rest at one end point of its motion. When it gets to the other extreme, the string is "cut" by releasing it. The question involves how the pendulum bob will move after it is released: will it move back retracing its path, due to its angular momentum and centripetal force; will it move downward and slightly toward the original path, due to its previous motion; will it move straight downward, due to gravity alone; or will it move downward and continue to move slightly away from its original path, due to its inertia? Click your mouse on the photograph above to see an mpeg video of the demonstration. Click here to see video that stops when the pendulum gets to its maximum amplitude, just before it is released; this video can be used to set up the question so that the class can vote on the outcome.

SUGGESTIONS: See Question of the Week #104 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA unknown)

EQUIPMENT: Galileo's pendulum setup modified as shown in the photograph.

SETUP TIME: 15 minutes.