bearings

are a common type of rolling-element bearing, a kind of bearing.  The term ball bearing sometimes means a bearing assembly which uses spherical bearings as the rolling elements. It also means an individual ball for a bearing assembly. The remainder of this entry uses the term ball for the individual component and ball bearing or just "bearing" for the assembly.

Ball bearings typically support both axial and radial loads and can tolerate some misalignment of the inner and outer races.  Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area that spherical shapes provide.

Types of bearings include linear/axial (along the same line as an axis (coaxial) or centerline) and rotary/radial (line drawn along a vector). A linear allows motion along a straight line, for example a drawer being pulled out and pushed in. A rotary bearing or thrust bearing allows motion about a center, such as a wheel on a shaft or a shaft through a housing. Common kinds of rotary motion include both one-direction rotation and oscillation where the motion only goes through part of a revolution. Other kinds of bearings include spherical bearings such as ball joints which are used in car suspensions and some computer mice.

There are six-(6) common principles of operation:

1. sliding bearings, usually called "bushings", "journal bearings", "sleeve bearings", "babbitt bearing" or "plain bearings"
2. rolling-element bearings such as ball bearings and roller bearings
3. jewel bearings, in which the load is carried by rolling the axle slightly off-center
4. fluid bearings, foil bearing, air bearing or gas bearing, in which the load is carried by a gas or liquid
5. magnetic bearings, in which the load is carried by a magnetic field
6. flexure bearings, in which the motion is supported by a load element which bends.