Leonardo da Vinci studied a ball bearing as a machine element for reducing friction between moving surfaces.
His notebooks contain sketches of balls positioned between rings or tracks so that rotation would involve rolling rather than sliding. Rolling contact generally produces less friction than sliding contact, a principle central to modern bearings. Leonardo’s studies show that he understood the value of separating moving surfaces with free-rolling elements.
The design was not necessarily the first idea of a rolling bearing, and Leonardo did not invent every form of bearing. Earlier devices used rollers and other methods to support loads. His importance lies in documenting a clear ball-bearing concept during the Renaissance and connecting it to mechanical motion.
Modern ball bearings use carefully manufactured balls, races, cages, seals, and lubricants. Leonardo’s sketches lacked the precision materials and manufacturing methods needed for modern high-performance bearings, but the underlying mechanical principle remains recognizable.