Leonardo da Vinci studied the ball bearing, a mechanical element that reduces friction by placing rolling balls between moving surfaces.
Around 1498, Leonardo made drawings showing balls arranged between a rotating component and a stationary support. The principle is simple: rolling contact generally creates less resistance than sliding contact. His sketches are often cited as an early recorded design for a modern-style bearing.
Leonardo did not invent the general idea of reducing friction with rollers. Ancient and medieval builders used rollers to move heavy objects, and later engineers developed many forms of bearings. His contribution was the clear mechanical study of enclosed rolling balls and the problem of keeping them separated so they would not interfere with one another.
The ball bearing became especially important during the Industrial Revolution, when machines needed reliable rotating shafts. Modern bearings may use steel, ceramic, or other materials and can include cages, seals, and lubrication. Leonardo’s drawings show the principle, but not a mass-produced bearing equivalent to those used in modern machinery.