When using a lever, in order to save labor, a lever with a power arm longer than a resistance arm should be used; If you want to save distance, you should use a lever with a force arm shorter than a resistance arm. 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. In general, it is impossible to save effort and move less distance.
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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: distance (moment) from fulcrum to stress point * stress = distance (arm of force) from fulcrum to stress point * force, so it is a lever.
Levers also have labor-saving levers and labor-saving levers, 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. Torque); But we have to press down for a distance, and the stressed end only moves a little. There is also a laborious lever.
Roadside crane, fishing hook at the tip of the whole pole, fulcrum at the end, hydraulic press 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.