Leonardo da Vinci sketched a ball bearing that used loose balls between moving surfaces to reduce friction.
The balls in a bearing roll rather than allowing two surfaces to slide directly against each other. This reduces friction and helps rotary motion become smoother. Leonardo’s drawings from the late fifteenth century show a cage-like arrangement intended to keep the balls separated while they move.
Leonardo did not invent every later feature of the modern ball bearing, and his design was not necessarily manufactured as a working industrial component. Nevertheless, the sketch is an important early record of the rolling-bearing principle. It should not be confused with a plain bearing, where surfaces slide against one another, or a roller bearing, which uses cylindrical rollers instead of balls.