Mechanical advantage (M.A.)
If a lever can be used to overcome a load of 50 N by applying an effort of 10 N, the lever is said to have a mechanical advantage of or 5.
Some machines are designed to overcome a load much greater than the effort used, for example, a spanner used to undo a tight bolt or a screw jack to lift a motorcar. In such cases the mechanical advantage is greater than 1.
In certain other machines the mechanical advantage is less than I, and in these the effort is greater than the load. It is not generally realized that a bicycle is a machine with a mechanical advantage of less than I. Under ordinary conditions the resistance to the motion of a bicycle along a level road is comparatively small, and therefore.a large mechanical advantage is unnecessary. Thus, although a cyclist works at a “mechanical disadvantage he nevertheless gains in the speed with which he can travel. On the other hand, the fact that the mechanical advantage of a bicycle is less than I becomes painfully obvious when we begin to ascend a hill. Whereas previously only a small amount of work had to be done against friction and air resistance, we now have to do a vastly increased amount against the force of gravity. Under these conditions it is usually easier to dismount and walk, unless the mechanical advantage of the bicycle can be increased by using a low gear (see gears in Fig. 8.14).