Leonardo da Vinci sketched a ball bearing for reducing friction between moving parts.
His late-15th-century studies included balls placed between rings so that surfaces could move with rolling contact instead of sliding directly against one another. This arrangement is recognizable as the basic principle of a ball bearing.
The design addressed a practical mechanical problem. Sliding friction wastes energy and creates wear, while rolling elements can make rotation smoother. Leonardo’s version also considered how to keep the balls separated, a difficulty that remains important in bearing design.
Leonardo was not the sole inventor of every bearing concept, and similar rolling devices existed in earlier mechanical traditions. The careful sketch is significant because it shows a clear bearing arrangement within his systematic studies of machines. Modern ball bearings add manufactured races, cages, lubrication, and precise materials.