PURPOSE: To model the forces occurring in the arm.

DESCRIPTION: Force applied by the biceps (left), pulling up with the hand: Apply 2.5 kg to the biceps cable to support the unloaded forearm. The forearm may be kept at equilibrium by the simultaneous addition of masses in the ratio of 10:1 at the biceps and at the hand. The torques are balanced almost independently of the angular position of the arm.

Force applied to the triceps (right), pushing down with the hand: Hang the spring scale between the top hook and the hand hook, and attach the hanger to the triceps cable. Add masses to the hanger to determine how much force in the triceps is necessary to push down with the force read on the scale.



EQUIPMENT: Arm model, 0.5 kg and 1.0 kg hangers, spring scale, three 5 kg, one 1 kg, and three 0.5 kg weights.

SETUP TIME: 5 min.

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