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摩擦力的作用点,常见到的有两种画法,如图1(甲)、(乙)。到底哪一种是正确的?两种画法是否可以任意选取?对这个问题,我认为有探讨的必要。
The point of friction is commonly seen in two ways, as shown in Figure 1(a) and (b). Which one is correct and whether the two methods can be arbitrarily selected? I think there is a need for discussion on this issue.