Leonardo da Vinci studied a ball bearing using spheres placed between two rings to reduce friction.
His notes from the late fifteenth century show an understanding that rolling contact can be more efficient than sliding contact. In the design, balls separate moving surfaces so that one ring can rotate more easily relative to the other.
Leonardo’s drawing is commonly cited as an early ball-bearing concept. It was not the first complete modern bearing assembly, and there is no firm evidence that he manufactured a standardized bearing for practical use.
Ball bearings later became important in clocks, machines, bicycles, vehicles, and industrial equipment. Their advantage comes from replacing much of the rubbing motion between surfaces with rolling motion, although lubrication and material wear still matter.