Leonardo da Vinci sketched a ball-bearing mechanism while studying ways to reduce friction between moving surfaces.
His drawings show balls arranged between concentric rings, allowing one ring to rotate while the balls roll rather than slide. Rolling contact generally creates less friction than sliding contact, making the principle useful for shafts, wheels, and other moving machinery.
Leonardo's notes from the late fifteenth century are among the earliest known drawings of a ball bearing. The sketch is often described as an early bearing concept, not proof that Leonardo invented every form of the modern ball bearing. Practical bearing designs developed gradually, and later engineers improved cages, materials, lubrication, and manufacturing precision.
The familiar modern bearing includes a raceway and often a cage that keeps the balls separated. Leonardo's open design did not necessarily solve all those engineering problems, but it clearly illustrates the central idea: interposing rolling elements between two moving surfaces.