<P> The simple machine called a wheel and axle refers to the assembly formed by two disks, or cylinders, of different diameters mounted so they rotate together around the same axis. The thin rod which needs to be turned is called the axle and the wider object fixed to the axle, on which we apply force is called the wheel . A tangential force applied to the periphery of the large disk can exert a larger force on a load attached to the axle, achieving mechanical advantage . When used as the wheel of a wheeled vehicle the smaller cylinder is the axle of the wheel, but when used in a windlass, winch, and other similar applications (see medieval mining lift to right) the smaller cylinder may be separate from the axle mounted in the bearings . It cannot be used separately . </P> <P> Assuming the wheel and axle does not dissipate or store energy, that is it has no friction or elasticity, the power input by the force applied to the wheel must equal the power output at the axle . As the wheel and axle system rotates around its bearings, points on the circumference, or edge, of the wheel move faster than points on the circumference, or edge, of the axle . Therefore, a force applied to the edge of the wheel must be less than the force applied to the edge of the axle, because power is the product of force and velocity . </P> <P> Let a and b be the distances from the center of the bearing to the edges of the wheel A and the axle B. If the input force F is applied to the edge of the wheel A and the force F at the edge of the axle B is the output, then the ratio of the velocities of points A and B is given by a / b, so the ratio of the output force to the input force, or mechanical advantage, is given by </P> <Dl> <Dd> M A = F B F A = a b . (\ displaystyle MA = (\ frac (F_ (B)) (F_ (A))) = (\ frac (a) (b)).) </Dd> </Dl>

Explain how a wheel & axel does work