Upward Impending Motion

A square-threaded screw jack is a mechanical device widely used for lifting heavy loads or applying considerable force. Its operation is based on converting the force applied at its handle into a torsional moment, causing the upward impending motion of the screw. This movement is accomplished by overcoming the static friction between the threads...

Consider a square-threaded screw jack. Applying a force at its handle results in a torsional moment, which causes upward impending motion of the screw. This is achieved by overcoming the static friction between the threads of the screw and the jack.

Consider the completely unraveled thread as a block in contact with the groove of the jack...