Leonardo da Vinci studied a ball bearing as a device for reducing friction between moving parts.
Leonardo’s notebooks contain drawings of balls placed between rings, allowing one surface to move more easily against another. The principle is the same as that of a modern rolling-element bearing: rolling contact generally produces less sliding friction than two surfaces rubbing directly together.
His sketches are often cited as an early record of the ball-bearing concept, although ball-like rollers and related mechanisms had appeared in earlier mechanical contexts. Leonardo’s contribution was his systematic study of mechanical motion and his recognition of how rolling elements could improve machines.
A ball bearing is not the same as a gear. Gears transmit motion and torque through toothed wheels, while bearings support rotating shafts and reduce resistance. Modern ball bearings use precisely shaped balls, races, cages, lubrication, and carefully selected materials. Leonardo’s Renaissance drawings were conceptual studies rather than mass-produced industrial components.