Leonardo da Vinci studied and drew ball-bearing mechanisms as a way to reduce friction between moving parts.
His notebooks include sketches of balls placed between rings or tracks so that sliding friction could be replaced by rolling friction. One famous design shows a separator intended to keep the balls from touching one another, an important feature because freely packed balls could rub together and interfere with motion. These drawings are associated with Leonardo’s investigations during the late fifteenth century.
Leonardo did not invent every principle behind rolling bearings, and his sketches were not the same as a modern standardized bearing. Industrial ball bearings developed much later, after advances in manufacturing made accurately shaped steel balls and races possible. The historical importance of Leonardo’s work is that it shows an early, clearly recorded attempt to control friction mechanically. Modern bearings remain essential in wheels, motors, turbines, and many precision machines.