PURPOSE: To demonstrate weightlessness in free fall.

DESCRIPTION: A small mass is attached to the inside center of a beaker using a rubber band. The mass is hung over the edge of the beaker, as in the photograph, and the cup is held in the air and released. Because the mass becomes weightless in free fall, there is no force pulling on the rubber band, so the rubber band pulls the mass into the beaker.

An interesting variation of this is to hold the cup upside down, with the mass hanging out of the cup, then release it. Ask the students what will happen when the cup is released: (a) The mass will extend the rubber band, like a parachute, (b) The mass will be pulled up into the cup, or (c) The cup will fall with the mass in its original position.

SUGGESTIONS:

REFERENCES: See Demonstration Reference File for lots of argument regarding this topic.

EQUIPMENT: Teflon beaker with 50 gram mass attached to the bottom by a rubber band, as photographed.

SETUP TIME: None.

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