Leonardo da Vinci sketched a ball bearing that used rolling balls to reduce friction.
In studies dating to the late fifteenth century, Leonardo explored arrangements in which balls moved between rings or tracks. The basic purpose was to prevent two surfaces from sliding directly against each other. Rolling contact generally produces less friction than sliding contact, making rotation easier.
His drawings show that he understood an important bearing problem: balls must be kept from crowding together. Some designs include separators or cage-like arrangements, although the sketches are not a single standardized bearing specification. Leonardo did not create the industrially manufactured ball bearings used in modern machines.
The idea is also distinct from a roller bearing, which uses cylindrical rollers rather than balls. Both reduce friction through rolling motion, but the shape of the rolling elements affects load capacity, alignment, and performance.