A rolling-element bearing is a bearing which carries a load by placinground elements between the two pieces. The relative motion of thepieces causes the round elements to roll (tumble) with little sliding.

oneof the earliest and best-known rolling-element bearings are sets oflogs laid on the ground with a large stone block on top. As the stoneis pulled, the logs roll along the ground with little sliding friction.As each log comes out the back, it is moved to the front where theblock then rolls on to it. You can imitate such a bearing by placingseveral pens or pencils on a table and placing your hand on top ofthem. See "bearings" for more on the historical development of bearings.

Arolling-element rotary bearing uses a shaft in a much larger hole, andcylinders called "rollers" tightly fill the space between the shaft andhole. As the shaft turns, each roller acts as the logs in the aboveexample. However, since the bearing is round, the rollers never fallout from under the load.

Rolling-element bearings have theadvantage of a good tradeoff between cost, size, weight, carryingcapacity, durability, accuracy, friction, and so on. Other bearingdesigns are often better on one specific attribute, but worse in mostother attributes, although fluid bearings can sometimes simultaneouslyoutperform on carrying capacity, durability, accuracy, friction,rotation rate and sometimes cost. only plain bearings have as wide useas rolling-element bearings.