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何谓共点力,书中有明确的定义:几个力如果都作用在物体的同一点,或者它们的作用线相交于同一点,这几个力就叫做共点力,对作用点是同一点的情况,学生比较容易理解和掌握,对力的作用线交于一点的情况,学生往往不易理解,也不易判断。为弄清这一问题,我在总复习时,突出讲了这样一个结论:如果物体只受互相不平行的三个外力作用(不管三个力的作用点是否相同)处于平衡状态,这三个力的合力必然为零,三个力的作用线必然交于一点,即是共点力。上述结论可以用反证法推证: 如图1:均匀杆AB 只受到三个力F_1、F_2、F_3
What is the common point force? The book has a clear definition: if several forces act on the same point of an object, or their line of action intersects at the same point, these forces are called common point forces, and they are the same point of action. Under the circumstances, students are relatively easy to understand and master. When the line of force is reached at a point, students are often difficult to understand and difficult to judge. In order to clarify this issue, I highlighted the conclusion that if an object is only balanced by three external forces that are not parallel to each other (whether or not the three forces have the same effect point), these three The resultant force of force must be zero, and the line of action of the three forces must be given at one point, that is, a common point force. The above conclusions can be deduced using counter-evidence: Figure 1: The uniform rod AB is subjected to only three forces F_1, F_2, F_3