You should use a lever whose arm of force is shorter than that of resistance. Therefore, the use of levers can save manpower and distance. However, if you want to save energy, you must move more distance; If you want to move a shorter distance, you must work harder. It is impossible to save energy and move the distance. It is from these axioms that Archimedes discovered the lever principle on the basis of the "center of gravity" theory, that is, "when two heavy objects are in equilibrium, their distance from the fulcrum is inversely proportional to their weight. The fulcrum of the lever does not have to be in the middle. A system that satisfies the following three points is basically a lever: fulcrum, force point and force point. The formula is written as follows: power× power arm = resistance× resistance arm, that is, F 1×l 1=F2×l2, which is a lever. The extension rod of power arm also has labor-saving rod and labor-saving rod, which have different functions. For example, there is an air pump that is pedaled by feet or a juicer that is pressed by hands, which is a labor-saving lever. Force distance); But we have to press it down for a distance, and the stressed end only moves a little. There is also a laborious lever. For example, the crane on the roadside, the fishing hook is at the tip of the whole pole, the fulcrum is at the end, and the hydraulic press is in the middle (torque >; Arm of force), this is a laborious lever, but it is hard to get that the middle point of force will move a considerable distance as long as it moves a short distance. Both levers are useful, but it is necessary to evaluate whether it is necessary to save labor or range of motion. There is another thing called shaft, which can also be used as a lever, but the performance may sometimes be added with the calculation of rotation. Archimedes, an ancient Greek scientist, famously said, "If you give me a fulcrum, I can pry up the earth", which is not only an inspiring aphorism, but also has a strict scientific basis.