PURPOSE: To illustrate weightlessness in free fall.

DESCRIPTION: A mass hangs from a spring over the edge of a cup. Raise the pole vertically and release. Because the mass becomes weightless in free fall, the ball will be pulled into the cup immediately when the system begins to fall. Clicking on the image at right, above, will show a short MPEG video of this demo in action. A slow-motion version is also available.

SUGGESTIONS:

See Question of the Week #223 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 1G20.38) This demonstration was suggested by Einstein.

EQUIPMENT: Koosh ball suspended from spring in mortar mounted on pole, as photographed.

SETUP TIME: None.