A bearing is a mechanical element that limits relative motion to a desired range of motion and reduces friction between moving parts.
Bearings are designed to provide free linear motion of moving parts or free rotation about a fixed axis, or to prevent motion by controlling the vector of normal forces acting on moving parts. Most bearings facilitate the desired motion by minimizing friction.
Bearings can be broadly classified according to different methods such as the type of operation, the allowed motion or the direction of the load (force) applied to the part.
A rotary bearing supports a rotating component such as a rod or shaft within a mechanical system and transfers axial and radial loads from the load source to the structure that supports it. The simplest bearing is a plain bearing, which consists of a shaft that rotates in a hole.
Friction is reduced by lubrication. In ball and roller bearings, to reduce sliding friction, rolling elements of rollers or balls with a circular cross-section are placed between the races or journals of the bearing assembly.
A wide variety of bearing designs can be correctly tailored to different application needs to maximize efficiency, reliability and durability.