Lever is a simple machine which was invented by Archimedes. In his book The Balance of Plane Graphics, he clearly put forward the basic principle of lever for the first time. He once said, "Give me a fulcrum and lever long enough, and I can pry up the earth." . However, we can't find a lever with such a solid length, and we can't find the starting point and fulcrum, so prying up the earth is just an illusion of Archimedes. The fulcrum of the lever does not have to be in the middle. The system software that achieves the following three points is mostly lever: fulcrum, stress point and support point.
Among them, the formula calculation is written as follows: the distance between fulcrum and supporting point (torque) * supporting force = the distance between fulcrum and applying point (arm of force) * reaction force, so it is a lever. Lever is also a saving lever and a laborious lever, which have different functions. When using a lever, if the lever is stationary or rotates at a uniform speed around the fulcrum, then the lever is in a state of balance. Arm of Force × Driving Force = Resistance Arm× Friction Resistance, that is, L 1×F 1=L2×F2, which can evolve into F 1/F2=L2/L 1. The balance of lever is not only related to driving force and friction resistance, but also related to the point and direction of force. A lever is a hard rod that can rotate around a fulcrum.
When an external force acts on any part inside the lever, the response of the lever is its actual operating system; If the acting point of the external force is the fulcrum, the lever will not react easily.