Lever

Lever, simple machine usually consisting of a rigid bar or rod, designed to rotate about a fixed point called the fulcrum. The effect of any force applied to a lever is to rotate the lever about the fulcrum. The rotational force is in direct proportion to the distance between the fulcrum and the applied force. For example, a mass of 1 kilogram being 2 metres from the fulcrum can balance a mass of 2 kilograms at a distance of 1 metre from the fulcrum.

In the crowbar, one type of lever, a relatively small effort is applied at the end farthest from the fulcrum to lift a heavy weight that is close to the fulcrum. Many other common tools and instruments (including the wheelbarrow and the nutcracker) utilize the principle of the lever. See Machine.