Leonardo da Vinci studied a ball bearing mechanism to reduce friction between moving surfaces.
His sketches from around 1498 show balls positioned between rings so that one surface could rotate more easily against another. The balls acted as rolling elements, replacing much of the sliding friction that would otherwise occur. Leonardo’s arrangement is widely cited as an early example of a modern-style bearing concept.
The idea was valuable because friction wastes energy, produces heat, and causes wear. A bearing can reduce those effects, but it must also keep the rolling elements spaced apart and support the loads placed on the rotating shaft. Leonardo’s drawing included a cage-like arrangement intended to stop the balls from crowding together.
Leonardo did not create the industrial ball-bearing industry. Practical bearings required later advances in metallurgy, precision machining, lubrication, and manufacturing. Modern ball bearings use hardened steel, ceramic, or other materials and are produced to tight tolerances.