运用系统的动能定理时,经常涉及到内力做功的问题,许多学生难以理解.虽然课程标准对内力做功的问题要求不高,但为了学生能更深入地理解动能定理和机械能守恒定律等功能关系,掌握一些常见的内力做功问题是非常必要的.众所周如,系统的内力总成对出现.即一对作用力和反作用力总是大小相等方向相反,同时产生同时消失.所以系统内力的矢量和总是为零.但是作用力与反作用力做的功却不一定等值反号.另一方面功能原理仅在惯性参照系中成立(一般以地面为参照系),当系 When using the kinetic energy theorem of the system, it often involves the problem of internal force doing work, which is difficult for many students to understand.Although the curriculum standard does not require much internal force work, in order for students to have a deeper understanding of the functional relationship of kinetic energy theorem and conservation of mechanical energy, It is very necessary to master some common problems of internal force and accomplishment .At the end of the week, the system’s internal force assembly pairs appear. That is, a pair of force and reaction force are always equal in size in the opposite direction and at the same time disappear. And always zero, but the work done by force and reaction force is not necessarily the equivalent number. On the other hand, the functional principle is only established in the inertial frame of reference (usually based on the ground)