Leonardo da Vinci studied a ball bearing using rolling balls to reduce friction between moving surfaces.
His notebooks contain a design in which balls move within a cage, preventing them from crowding together while allowing a ring to rotate. The arrangement resembles the basic principle of modern rolling-element bearings: rolling contact replaces much of the sliding contact that would otherwise create resistance.
Leonardo’s study is frequently cited as an early bearing concept, but it was not a complete modern industrial bearing. Manufacturing tolerances, materials, lubrication, and precision assembly were not yet advanced enough for widespread practical use. The design nevertheless shows that he understood how rolling elements could improve mechanical motion.
Ball bearings are now used in machines ranging from bicycles to electric motors. They should not be confused with plain bearings, which support a shaft through sliding contact rather than balls or rollers.