What basic mechanical component did Leonardo da Vinci study to reduce friction?

Leonardo da Vinci studied the ball bearing as a way to reduce friction between moving surfaces.

His notes and drawings from the late fifteenth century show balls arranged so that one surface could roll over another instead of sliding across it. Rolling contact generally produces less friction than sliding contact, making the idea useful for machines with rotating parts. Leonardo’s sketches are among the early recorded studies of this principle.

The drawings do not prove that Leonardo invented the modern precision ball bearing. His design still faced practical problems, including keeping the balls separated and preventing them from bunching together. Later engineers developed cages, hardened materials, accurate machining, and lubrication that made reliable bearings possible.

A ball bearing is also not the same as a gear. Gears transmit motion and torque through teeth, while bearings support rotating shafts and reduce resistance. Leonardo’s interest in bearings formed part of his broader investigation of gears, axles, pulleys, and other machine elements.