Leonardo da Vinci studied a ball bearing as a rotating mechanical component for reducing friction.
His sketches show balls placed between surfaces so that the balls would roll instead of allowing one surface to slide directly against another. This arrangement is the basic principle of a ball bearing: rolling contact generally produces less friction than sliding contact.
The drawings are usually associated with Leonardo’s work around 1498. He appears to have been interested in the problem of friction while designing machines, although he did not create the standardized, enclosed bearings used in modern machinery.
Leonardo’s bearing is often described as an invention of the ball bearing, but similar rolling elements had appeared in earlier mechanical contexts. His importance lies in the clarity of his analysis and in applying the idea systematically to machine design.