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在用杠杆做功的过程中,杠杆的机械效率高低和杠杆所克服的无用阻力有关。对于一个杠杆,使用中只有尽可能的减小无用阻力,才能提高它的机械效率。一般认为杠杆的无用阻力主要是杠杆的摩擦和自重。对于杠杆的摩擦属于无用阻力是毫无疑问的。但把所有的杠杆自重都认为是无用阻力,是值得探讨的。根据杠杆做功时总是使它的一端向上或向下移动,我们可以把杠杆分两种情况来讨论:一种是在动力做功时杠杆的重心被升高,如图1所示,图中只给出两
In the process of doing work with a lever, the mechanical efficiency of the lever is related to the useless resistance that the lever overcomes. For a lever, only the useless resistance is reduced as much as possible in order to increase its mechanical efficiency. It is generally believed that the useless resistance of leverage is mainly the friction and weight of leverage. There is no doubt that the friction of the lever belongs to useless resistance. However, considering all leverage as weightlessness is worth exploring. When working on a lever, it always moves one end up or down. We can discuss the lever in two situations: one is that the lever’s center of gravity is raised when the power is done, as shown in Figure 1. Give two