Bearings
Bearings are relatively small components placed between moving parts to reduce friction with movement. They can be made of many different materials and can be of various sizes and designs. Bearings are used in various applications; they can be found in engines, assembly lines, fans, hand tools, and roller-skates.
There are two classifications for bearings: linear and rotary. These classifications are based on the motions for which they are designed. A linear bearing moves in a straight line and is used for pushing and pulling motions, like a drawer opening and shutting. A rotary bearing is designed for radial motion, like that of a wheel spinning. Rotary bearings are also commonly referred to as thrust bearings.
Bearings are usually small enough to hold in the palm of a hand, but they can be as large as ten feet in diameter. Bearings this large are used in places like hydroelectric power plants. Ball bearings have been used for many years, and their low cost ensures that they will continue to be used in the future.