A ball screw is a form of mechanical actuator that combines the use of a screw with ball bearings. Consisting of a screw shaft and a nut that contains one or more balls which roll between their matching helical grooves, ball screws function by converting rotational motion to linear motion. They accomplish this by using rolling balls in the helical grooves of the screw to replace sliding friction with rolling friction. As a result, ball screws are useful for transmitting motion smoothly with less wear on internal components.