Leonardo da Vinci sketched a ball bearing mechanism using rotating balls to reduce friction.
In his late-15th-century studies, Leonardo explored how balls placed between moving surfaces could allow one part to rotate more freely against another. The balls separated the surfaces and replaced much of the sliding friction with rolling friction, the central idea behind a ball bearing.
His drawing is often celebrated as an early bearing concept, but Leonardo did not invent every bearing arrangement used today. Ancient and medieval engineers had used rollers and other methods to reduce friction, while modern ball bearings require carefully manufactured races, cages, and hardened balls.
Leonardo’s version also shows a practical challenge: loose balls can bunch together and rub against one another. Later bearing designs addressed that problem with cages and more precise geometry.