Leonardo da Vinci designed a ball bearing using small metal balls to reduce friction.
Leonardo’s notebooks contain sketches of a bearing in which balls move between surfaces, allowing one part to rotate more freely against another. The basic principle is rolling friction: rolling objects generally resist motion less than sliding surfaces do.
His design included a cage-like arrangement intended to keep the balls separated. That detail is important because loose balls can bunch together and increase friction. Although Leonardo recognized the mechanical advantage of rolling elements, his bearing was not the standardized, precision-manufactured component used in modern machinery.
The invention is often credited to Leonardo in popular histories, but earlier forms of rolling-element bearings existed in antiquity. Leonardo’s importance lies in his clear Renaissance-era design and his attention to keeping the balls from rubbing against one another.