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通常情况下,确定滑动摩擦力的大小、方向、作用点是比较容易的,但有时却较困难,下面通过例题的分析来说明,在复杂的情况下,如何确定滑动摩擦力的三要素。 一、确定滑动摩擦力的作用点 相互接触、且接触面粗糙的两物体间发生相对滑动时,若存在相互挤压的压力N,则有滑动摩擦力f产生。N大处f大,N小处f小,N为零处f也为零。这一结论对相互接触且有相对滑动的任两物体,以及将此两物体分割成众多质点时也成立。可见f的作用点始终和N的作用点重合。于是,当滑动摩擦力的作用点难以确定时,可以转而寻找比较容易确定的压力作用点。
Under normal circumstances, the size, direction, and action point of the sliding friction are relatively easy to determine, but sometimes it is more difficult. The following example illustrates how to determine the three factors of sliding friction under complex conditions. First, to determine the role of sliding friction point of contact with each other, and the contact surface between the two objects are relatively slid, if there is mutual pressure N, there will be a sliding friction force f. N is large at f, N is small at f, and N is zero at zero. This conclusion holds true for any two objects that are in contact with each other and have relative sliding, and when these two objects are divided into many mass points. It can be seen that the point of action of f always coincides with the point of action of N. Thus, when the point of action of the sliding friction force is difficult to determine, it is possible to search for a more easily determined pressure application point.