Generally speaking, a bearing is a device that is used to enable rotational or linear movement, while reducing friction and handling stress. Resembling wheels, bearings literally enable devices to roll, which reduces the friction between the surface of the bearing and the surface it’s rolling over. It’s significantly easier to move, both in a rotary or linear fashion, when friction is reduced—this also enhances speed and efficiency.
How Bearings Work
In order to serve all these functions, bearings make use of a relatively simple structure: a ball with internal and external smooth metal surfaces, to aid in rolling. The ball itself carries the weight of the load—the force of the load’s weight is what drives the bearing’s rotation. However, not all loads put force on a bearing in the same manner. There are two different kinds of loading: radial and thrust.
A radial load, as in a pulley, simply puts weight on the bearing in a manner that causes the bearing to roll or rotate as a result of tension. A thrust load is significantly different, and puts stress on the bearing in an entirely different way. If a bearing (think of a tire) is flipped on its side (think now of a tire swing) and subject to complete force at that angle (think of three children sitting on the tire swing), this is called thrust load. A bearing that is used to support a bar stool is an example of a bearing that is subject only to thrust load.