1灵活选取研究对象动量定理的研究对象通常是单个物体.对单个物体的运动,研究对象的选取并不困难.但对于连续介质的持续作用,或者多个物体组成的系统问题,灵活合理的选取研究对象往往是解决问题的关键. 1 The research object of the flexible selection of the momentum theorem of the research object is usually a single object. For the movement of a single object, the selection of the research object is not difficult. However, the continuous effect of the continuous medium or the system problem of multiple objects is selected flexibly and reasonably. The research object is often the key to solving the problem.