Leonardo da Vinci sketched a ball-bearing mechanism that used rolling balls to reduce friction between moving parts.
Around 1498, Leonardo studied friction and mechanical motion while working on engineering designs. His notes include a device in which balls move between rings, separating surfaces that would otherwise rub directly against one another. The principle is the same basic idea used by later ball bearings.
The design is significant because rolling contact can greatly reduce friction compared with sliding contact. Leonardo’s arrangement also attempted to prevent the balls from crowding together, an important practical issue in bearing design.
Leonardo did not invent the modern standardized ball bearing in the industrial sense. Earlier cultures had used rollers and other friction-reducing methods, and modern bearings required later advances in manufacturing and materials. His drawing is best understood as an early documented bearing concept.