涉及摩擦力的各类问题是学生学习的难点.要正确分析摩擦力,往往需要对物体的其他受力情况、运动情况等有全面的认识,进行综合考虑.当影响摩擦力的一些因素发生“突变”时,摩擦力也可能随之改变,这类“突变”问题的剖 All kinds of problems involving friction are difficult for students to learn. To correctly analyze friction, it is often necessary to have a comprehensive understanding of the other stress conditions, motion conditions, etc. of the object and to consider it comprehensively. When some factors affect the friction occur, " In the case of a mutation, friction may also change, and this type of “mutation” problem