Ball bearings, long used in mechanics, have many functions today, including keeping automobiles running smoothly by reducing friction between the wheel and the chassis. The bearings today are typically contained in a round holder called a race, similar to the one Leonardo invented. Leonardo realized that there would be less friction if the balls didn't touch each other, so he built in separators that allow each ball to ball to rotate freely. This device was reinvented in 1772, almost 300 years after Leonardo first drew it.
