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Further information on Theory, Apparatus, Procedure, and Helpful Hints is available. Equipment is stored in Rockerfeller Rooms 402 and 403.
The sum of torques on a balanced rigid body must equal zero. The torques on the body are equal to the forces applied multiplied by the shortest perpendicular distance between their vector and the center of mass.
The equipment needed for this demo is:
Suspend the meter stick at the 50 cm mark by a spring scale hanging from a clamp on the ring stand. Note the weight of the meter stick. Then hang spring scales with equal masses on the ends of the meter stick. The weight of the spring scales must be accounted for. Now replace one of the masses with a smaller mass and calculate how far in the heavy mass must be moved in order for the stick to remain balanced. At each stage all the forces displayed on the scales can be explained by the equations being studied by the class.