PURPOSE: To illustrate conservation of angular momentum.
DESCRIPTION: Two masses which can slide along a crossarm can be moved to smaller radii by pulling on the chain hanging down through the center of the apparatus. With the masses at the largest radius, start the system rotating. Pulling the chain pulls the masses inward, reducing the moment of inertia and causing the system to rotate with a greater angular velocity. Slowly releasing the chain increases the angular momentum and thus reduces the angular velocity.
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SUGGESTIONS: Keep your chin back.
See Question of the Week #76 for information on using this demonstration to enhance class involvement.
REFERENCES: (PIRA 1Q40.20) See Demonstration Reference File for paper from The Physics Teacher describing this apparatus.
EQUIPMENT: As photographed.
SETUP TIME: None.
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