Leonardo da Vinci sketched a ball bearing as a friction-reducing component with balls rotating inside a bearing.
In his studies of friction, Leonardo explored ways to keep moving surfaces separated by rolling elements rather than allowing them to slide directly against one another. One design places balls between rings or tracks, an arrangement that anticipates the basic principle of a modern ball bearing. Rolling contact generally reduces friction compared with sliding contact.
Leonardo’s drawings do not establish that he invented the complete standardized bearing used in modern machines. His sketches show an early recognition of the principle, while later engineers developed practical cages, materials, lubrication systems, and manufacturing tolerances. Ball bearings are now used in bicycles, electric motors, turbines, tools, and countless other machines. They are also different from roller bearings, which use cylindrical or tapered rollers instead of spherical balls.