Leonardo da Vinci drew a ball bearing using balls between moving surfaces to reduce friction.
In a bearing of this kind, rolling balls separate parts that move relative to one another. Rolling contact generally produces less friction than sliding contact, allowing a shaft or other component to turn more easily. Leonardo studied the principle while investigating machines and mechanical motion.
His sketches include arrangements in which balls are kept apart so they do not simply bunch together. This is an important feature of practical bearing design, because uncontrolled contact can increase friction and wear. Leonardo’s drawings demonstrate an early understanding of the principle, not the mass manufacture of modern precision bearings.
The concept is sometimes described as Leonardo’s invention of the ball bearing. A more cautious statement is that he produced an early documented design. Ancient and medieval engineers had used rollers and related friction-reducing devices, while modern bearings require precise materials, tolerances, and lubrication.