The wheel and axle is a simple machine.
The wheel and axle consists of a handwheel (a disc or lever arm with a handle) which turns an axle around which a chord is wound. A heavy weight attached to the chord can be lifted more easily because of mechanical advantage.
The mechanical advantage of a wheel and axle is the ratio of the radius of the wheel to the radius of the axle. If the radius of the wheel is four times greater than the radius of the axle, every time you turn the wheel once, your force will be multiplied four times.
Examples of wheel and axles are:
Bicycles, Ferris wheels, gears, wrenches, door-knobs and steering wheels.