Leonardo da Vinci studied the ball bearing, using freely rolling balls to reduce friction.
His sketches show balls placed between surfaces so that one part could move over another with rolling rather than sliding contact. This arrangement is the basic principle behind a ball bearing.
Leonardo explored the idea while studying machines and friction. The sketches are associated with the Codex Atlanticus and are often cited as an early example of a bearing using rolling elements, although similar concepts existed in earlier engineering traditions.
Leonardo did not create the standardized, sealed industrial bearings used today. Modern bearings depend on carefully manufactured races, cages, lubrication, and materials. His importance lies in recognizing how rolling balls could make mechanical motion more efficient.