The principle of force transformation of a screw jack is as follows:

The screw jack is mainly composed of a screw, a nut, a base, a tray and other parts. When the screw is rotated, relative movement occurs between the screw and the nut. Due to the small helix angle of the screw, according to the principle of screw transmission, a small torque can be transformed into a large axial force.

Specifically, when a force is applied to the handle of the screw to rotate it, through the rotational motion of the screw, the screw makes a helical forward or backward movement in the nut. Because the helix angle of the screw is usually smaller than the friction angle, the friction between the screw and the nut causes a large thrust or pull force in the axial direction, so that a heavy object can be lifted or lowered.

For example, suppose the pitch of the screw is p. When the handle is rotated one circle, the screw advances or retreats a distance of one pitch along the axial direction. If the force applied on the handle is F1, according to the relationship between force and torque and the efficiency of screw transmission and other factors, the force F2 generated in the axial direction can be much greater than F1. The magnification of this force is related to factors such as the helix angle and friction coefficient.

In short, the screw jack transforms a small human force into a large lifting force through screw transmission to realize the jacking operation of heavy objects.