How does a screw change turning force into lifting force?

A screw functions as a simple machine that modifies force and motion, and it can be understood mechanically as an inclined plane wrapped around a cylinder.1

When used as a power screw—such as in a screw jack—it converts torque (a turning moment) into linear thrust. This process works because the screw rotates within a stationary nut (or vice versa), forcing the helical rib to travel along the threads. By applying a relatively small force at the end of a long bar or handle to turn the screw, the device generates a significantly larger thrust force capable of lifting heavy objects.21

Essentially, the screw translates the rotational input into a linear output, providing a mechanical advantage that allows for the movement of heavy loads with much less effort than would be required to lift them directly.1