Leonardo da Vinci explored the ball bearing, using rolling spheres to reduce friction between moving surfaces.
His notebooks contain studies of balls placed between rings or surfaces so that motion would involve rolling rather than direct sliding. Rolling generally creates less resistance than sliding, making the arrangement useful for shafts and other rotating mechanisms.
Leonardo’s sketches date to the late 15th century and are frequently cited as an early investigation of the ball-bearing principle. He was not the inventor of every later bearing design, and his drawings do not represent a modern standardized bearing with sealed races and manufactured precision balls.
The idea mattered because friction limits the efficiency and durability of machines. Bearings became increasingly important in later mechanical engineering, especially as clocks, mills, vehicles, and industrial machinery required smoother rotation. Leonardo’s work shows his ability to study small mechanical details as well as large machines.