Have you ever wondered how cars and other motor vehicles run smoothly and quietly? As a child, I have always been in awe of how these powerful machines work. Later on, I understood that these machines run smoothly with the help of smaller machines called bearings. Bearings are important to the machines we use everyday, for without them, we would need to frequently replace broken machine parts due to the wear and tear of friction.

A bearing is a tool used to reduce the friction that occurs in machines. Friction is a kind of force which opposes the movement of a surface in sliding or rolling motion over another surface with which it is in contact. Bearings bear the frictional force which is set up by the moving surface of a machine part.

Bearings are categorized according to how they operate and the motions that they allow. The two common motions are linear and rotary. Bearings which allow linear motions are called linear bearings. These bearings allow motion in a straight line. An example of linear motion is the pulling and pushing of a drawer. Rotary motions, on the other hand, involve one direction rotation and oscillation, wherein the motion goes only through a part of a cycle, such as in the case of a wheel. Rotary bearings, therefore, allow motions which are concentrated on a center, like a wheel on a shaft.

Many applications use rotary bearings such as machine shafts, vehicle axles, and clock parts. The sleeve bearing, a simple cylinder which is inserted between the wheel and its axle, is the most basic rotary bearing. The roller bearing followed, wherein the sleeve is replaced by a number of cylindrical rollers, each behaving as a single wheel.

The operation of bearings includes six common principles. Sliding bearings are usually called "bushings", "journal bearings", "sleeve bearings", or "plain bearings". Rolling-element bearings include ball and roller bearings. Jewel bearings allow its load to be carried by an axle, which is rolled off-center. Fluid bearings, on the other hand, allow its load to be carried by a liquid or gas. In magnetic bearings, a magnetic field carries the load. In flexure bearings, the motion is given off by a load element which bends.

Bearings are said to have existed since the ancient times when Egyptian pharaohs started building and constructing their well know Pyramids of Giza. An initial type of linear bearing was used in Egypt to transport construction materials. These materials included large boulders and stones which were difficult to move and carry to the construction site. The arrangement of tree trunks under a sled helped transport bulky materials from one place to another. This principle serves as the basis of modern linear bearings.

An early model of the wooden ball bearing was used to support a rotating table. This was found from the remains of a Roman shipwreck. Leonardo Da Vinci was also said to have described a type of ball bearing during his time. But Galileo described the caged ball bearing in the 1600s, but it was only in 1794 that bearings were mounted as a set when Philip Vaughan got the first patent for a ball bearing. In 1907, the contemporary design of self-aligning ball bearings was manufactured by Sven Wingquist.

The early sliding and rolling-element bearings were wood, but some tried using other materials such as ceramic and glass. Today, plastics such as nylon and polyoxymethylene, and other metals such as steel and bronze are commonly used to produce bearings.