Leonardo da Vinci studied a ball bearing, using balls between moving surfaces to reduce friction.
His late-15th-century mechanical studies include a design in which balls roll within a raceway. Rolling elements can reduce sliding friction, allowing one part to rotate more easily against another. The principle is fundamental to many modern machines, from bicycles to electric motors.
Leonardo did not invent every form of bearing, and ancient engineers had already used rollers and related low-friction ideas. His importance lies in clearly recording a practical ball-bearing arrangement during the Renaissance and recognizing the value of separating moving surfaces with rolling bodies.
The design also shows Leonardo’s habit of investigating ordinary mechanical problems mathematically and experimentally. A bearing can reduce resistance, but it cannot eliminate friction entirely; contact, deformation, lubrication, and wear still affect performance.