试举力学一例 剖析内力作功

An Example of Inner-force＇s Doing Work

分四种情况讨论了叠放在一起的物体组成的系统，在运动中内力作功大于零、等于零、小于零的情况．

The system made up of subsance piled up together is discussed in four cases in whichthe work done by moving inner force is bigger than zero， as big as zero and less than zero.