Leonardo da Vinci sketched a ball bearing using freely moving spheres to reduce friction between surfaces.
His notebooks include studies of balls placed between rings or other supporting parts. The basic idea is to replace sliding contact with rolling contact, which can make rotary motion easier and reduce wear. Leonardo examined the concept while studying machines, motion, and friction.
Leonardo is often credited with an early ball-bearing design, but he did not invent the general use of rolling elements. Ancient and medieval devices used rollers and related principles, and later engineers developed practical bearings with cages, races, and standardized metal balls.
The word bearing describes a component that supports a moving load, while “ball bearing” specifies the rolling elements. Leonardo’s sketch was not a modern sealed bearing and was not necessarily manufactured as a finished machine part. Its historical importance is that it clearly explores a principle central to modern mechanical engineering.