Wheel and Axle, a simple machine consisting of a wheel (or crank) and an axle that turn on the same axis. Steering wheels, doorknobs, and screwdrivers are wheel-and-axle devices. A crank replaces the wheel in devices such as windlasses, bicycle pedals, and hand drills.
The wheel and axle can be regarded as a form of lever: the radius of the wheel corresponds to the force arm, to which force is applied; the radius of the axle corresponds to the resistance arm; and the axis of the axle corresponds to the fulcrum. A wheel and axle has a theoretical mechanical advantage (ratio of the force delivered by the machine to the force put into the machine, disregarding friction) equal to the radius of the wheel divided by the radius of the axle.