LINNEAR TRANSMISSION OF MOTION

LEVERS
A lever is a rigid bar that turns around a point called fulcrum. Various forces may act on the lever at the same time.
Each force produces specific torque, which is the force multiplied by its distance from the fulcrum.
When the force acting on opposite ends of a lever are equal,we say the lever is in equilibrium. We can express this mathematically as the Law of the Lever: F×d=R×r
F is the force of the effort that we use;d is its distance from the fulcrum;R is the resistance or load that we want to move; and r is its distance from the fulcrum
Classes of levers

A hand crank

A hand crank has two parts. One is connected to a rotating shaft and the other forms and handle. We can use a hand crank to apply forcé at a distance from the axis of the shaft. This make easy to turn. A crank is a Class 2 lever, so it obeys the Law of the Lever.

This link is a video of a hand crank: http://9gag.com/gag/a8W7jZY/a-hand-crank-gif-player