Ball bearings are used for rolling elements, such as skateboard wheels or the rotating parts of computer hard drives, or axial devices, such as a sliding drawer. They are generally designed to bear light loads, as heavy stress can cause the balls inside the bearings to become warped. Because of their limitations, ball bearings are usually used to roll or rotate lightweight objects.
Ball bearings work by situating a varied number of small spheres between two grooved rings, called races. There are generally two races: an inner race and an outer race. The inner race is fixed to an object, such as an axle shaft or a hub. Movement of the outer race causes the spheres to roll, based on their minimal contact with both the inner and outer race.
When the spheres move, the inner race may remain stationary while allowing the outer race's attachment (outer wheel or drawer, for example) to move freely. The minimal contact between the spheres and the races reduces friction, which allows more speed than a standard rotating or sliding device. Too much weight against the spheres may cause warping, which increases the friction and slows down the device. For heavier loads, roller bearings are recommended.