Most of the motion generated by joints in the human body are examples of levers.

Question

Most of the motion generated by joints in the human body are examples of levers. An example of a third class lever is the forearm; the force which generates the motion is located in between the pivot point and the resistance force. The elbow acts as the pivot point, the biceps muscle pulls up on the forearm to move the mass which is held in the hand. Imagine you are holding an object in your hand with your forearm horizontal and your upper arm vertical so your elbow creates a 90° angle. If your biceps attach to your forearm 0.0640 m from the elbow and make an angle of 30.0° with the vertical while a 3.14 kg mass is held in your hand 28.60 cm from the elbow, what force is exerted by the biceps muscle? Ignore the mass of the forearm. Number F=

Explanation / Answer

(3.14 x g) = 30.8N. (9.81 used for g).

Torque = (30.8 x 28.60) = 880.98 N/cm.

Perpendicular force component at muscle = (880.98 /6.40cm) = 137.65 N.

Force at 30 degrees = (137.65/cos 30) = 158.95N.

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