Leonardo da Vinci studied the ball bearing, using smooth rotating spheres to reduce friction.
His notebooks include sketches of balls placed between surfaces so that one part could move over another with less sliding resistance. The principle is simple: rolling contact generally creates less friction than direct sliding contact. Leonardo’s drawings show that he understood the usefulness of separating moving surfaces with freely moving balls.
The idea was relevant to mechanical systems such as rotating supports and machinery. Leonardo did not create the standardized, enclosed precision bearings used in modern engines, and his sketches should not be treated as evidence that he invented the complete modern bearing industry.
Later ball bearings required accurate manufacturing, hardened materials, cages, lubrication, and reliable dimensions. Leonardo’s importance is as an early documented thinker about the mechanism, not as the maker of a mass-produced modern component.