Leonardo da Vinci designed an early ball bearing using small rolling spheres to reduce friction.
In a ball bearing, balls are placed between an inner and outer ring or between surfaces that would otherwise rub directly. The balls roll as the parts move, replacing much of the sliding friction with rolling friction. Leonardo’s sketches show an arrangement intended to keep the balls separated so they would not bunch together.
The concept appeared in Leonardo’s engineering studies around the late fifteenth century. His design was not the modern standardized bearing used in machines today, and it is uncertain how far the sketch progressed toward practical manufacture.
Leonardo’s bearing is often cited as an early example of rolling-element engineering. It should not be confused with a flywheel, whose main purpose is storing rotational energy, or with a gear train, which transmits motion and changes speed or torque.