螺絲釘的原理 (The principle of a screw jack)
First, you need to prepare a big screw.
You hold the top of the screw. And put two fingers to hold the bottom of the screw. Spin the top of he screw.
And you will see the screw goes does slowly between your fingers.
Why?
Screw Jack is an example of the principle of tool. The more pitches are presented, the least force you need to use. Screw jack is used to join objects, but it also can lift up a heavy object. A crane is also used to lift up heavy objects without spending too much forces.