Question

Explain why the mechanical advantage of the class III lever is always less than 1.

Answer 1

The elbow is the fulcrum, and the muscles of the forearm apply the force between the elbow and the hand. The class 3 lever always has a mechanical advantage of less than 1, because the load travels a greater distance than the force travels. Consequently, the work requires more effort than would ordinarily be needed.

For the class III lever, "the force is applied between the fulcrum and the load"... So d/D, d being the distance from the fulcrum to the force, and D being the distance from the fulcrum to the load, is less than 1....

The advantage is that the acting distance of the force is less than the resultant distance traveled by the load. This principle allows smaller machines to move loads great distances.