Leonardo da Vinci sketched a ball bearing to reduce friction between moving surfaces.
Around 1498, Leonardo studied the use of loose balls between rings or tracks. The balls could roll rather than allowing two surfaces to slide directly against one another, reducing friction. His drawings are often cited as an early recorded concept for a modern-style rolling-element bearing.
The principle was not entirely unknown in earlier mechanical traditions, and Leonardo did not create the modern standardized bearing industry. His importance lies in clearly documenting a practical arrangement of rolling balls within a mechanical system and recognizing the friction problem it could address.
A ball bearing is not the same as a wheel, gear, or pulley. Those devices transmit motion in different ways, while a bearing supports a load and permits controlled rotation. Modern bearings use carefully manufactured races, cages, lubrication, and hardened materials; Leonardo’s sketch was an early conceptual design rather than a modern finished component.