Leonardo da Vinci sketched a ball bearing using balls between moving surfaces to reduce friction.
The principle is simple: rolling balls separate surfaces that would otherwise slide directly against one another. Rolling friction is generally lower than sliding friction, so the arrangement can make rotation easier and reduce wear. Leonardo’s notes show that he understood this useful mechanical relationship.
The drawing is often described as an early ball-bearing design, not as the invention of every bearing used today. Ancient and earlier engineers had used related rolling concepts, and modern bearings require precise materials, cages, lubrication, and manufacturing tolerances.
Leonardo’s design also included a cage-like arrangement intended to keep the balls separated. That detail is important because freely touching balls can rub together and reduce efficiency. His study illustrates how Renaissance notebook sketches could anticipate later machine components without immediately becoming standardized industrial products.