“... the balls... will touch in one point only between the load and its resistance...”
Leonardo da Vinci, The Madrid Codices (c. 1490)
Ball bearings are a low-cost method of allowing different parts of a mechanism to rotate past each other without much energy loss from friction. They have many uses, including in bicycles, gyroscopes, electric motors, and turbines. They did not come into general use until the Industrial Revolution, but the concept has been around for more than 2,000 years.
Roman Emperor Caligula (12-41 C.E.) had two large ships built at Lake Nemi. When the remains of these ships were recovered in the early 1930s, marine archeologists found the earliest known ball bearings. There were two types found—bronze spheres and wooden balls. The wooden ball bearings supported a rotating table, similar to a lazy Susan or dumbwaiter.
Prior to this discovery historians had believed that Leonardo da Vinci invented ball bearings.
Ball bearings became so widely used in factories, vehicles, and other machinery, that during World War II, the Allies made a concerted effort to bomb German ball bearing plants in order to disrupt the German war effort. The Germans had astutely stockpiled millions of bearings and were able to continue supplying factories despite ball bearing production being halved.
These days, for applications with high load, speed, and, or precision requirements, ball bearings are increasingly being replaced by fluid bearings, which use a layer of gas or liguid to support the load.
