Leonardo da Vinci studied and sketched an early form of the ball bearing.
His notebooks include a design in which balls move between rings, reducing direct contact between rotating surfaces. The basic purpose is the same as in modern ball bearings: rolling elements replace much of the sliding friction that would otherwise occur between two surfaces.
Leonardo’s concept is associated with his mechanical investigations in the late fifteenth and early sixteenth centuries. The sketch shows an understanding that the balls must remain separated so they do not bunch together and stop the mechanism. Modern bearings use carefully manufactured races, cages, lubrication, and precise materials, features that were not available in Leonardo’s workshop in their modern form.
Leonardo was not the only early thinker interested in reducing friction, and the history of bearings continued for centuries. Philip Vaughan received a patent for an improved ball-bearing design in Britain in 1794, long after Leonardo’s notebooks were made.