Leonardo da Vinci studied a ball bearing to reduce friction between moving surfaces.
His notebooks contain sketches of balls placed between rings or other supporting surfaces. The balls were intended to roll instead of allowing one surface to slide directly against another, reducing resistance. This is the basic principle behind modern rolling-element bearings.
Leonardo’s studies are commonly dated to the late fifteenth or early sixteenth century. He investigated friction, motion, and mechanical efficiency as part of a broader effort to understand machines. His drawings show an important mechanical idea, but they do not establish that he invented the complete standardized bearing used today.
A ball bearing is not the same as a gear, pulley, or wheel axle. Its defining feature is rolling contact between the balls and their races. Modern bearings also depend on precise manufacture, suitable materials, lubrication, and cages or retainers—features that developed long after Leonardo’s sketches.