Leonardo da Vinci drew a ball bearing to reduce friction between moving surfaces.
Around 1498, while studying friction and mechanical motion, Leonardo sketched a device using balls between two rings. The balls were intended to keep the rings from rubbing directly against each other. This is the essential operating principle of a ball bearing: rolling contact replaces much of the sliding contact that produces friction.
Leonardo’s drawings are among the earliest known illustrations of this idea. His design included separators so the balls would not crowd together, an issue that remains important in bearing construction. He did not create the modern standardized bearing industry, but his mechanical studies anticipated a useful engineering solution.
Modern ball bearings are used in bicycles, motors, wheels, turbines, and countless machines. They usually contain inner and outer races, rolling elements, and often a cage. Leonardo’s sketch should not be confused with a complete modern bearing specification; it was a conceptual design within his broader investigations of machines and motion.