Leonardo da Vinci studied the ball bearing as a way to reduce friction between moving parts.
Around 1498, Leonardo drew mechanisms using balls placed between surfaces so that sliding friction could be replaced by rolling friction. His sketches are among the earliest known studies of the principle, although rolling elements had appeared in simpler forms before Leonardo and he was not the sole inventor of the bearing.
In a bearing, rolling balls allow one ring or surface to move relative to another with less resistance than direct rubbing. Leonardo’s designs also explored cages or separators to keep the balls from bunching together. That detail is important because loose balls can collide and create unwanted friction rather than operating smoothly.
Modern ball bearings use carefully manufactured steel, ceramic, or other materials, plus lubrication and precise races. Leonardo’s drawings were conceptual and did not provide the industrial manufacturing accuracy required by modern bearings. His work nevertheless helped explain a key mechanical principle used throughout machines.