1) variable mass-point
变质量质点
1.
A theorem on kinetic energy for variable mass-point and formula of work of recoil internal forces are given and the reason of soft-rope query is discussed.
给出变质量质点的动能定理和一对反推内力作功的表达式，并由此给出软绳问题的正确解释。
2) point mass
质点质量
3) Metamorphic quality
变质质量
4) qualitative change and quantitative change
质变量变
5) Quantitative andqulitative
量变质变
6) quality variable
质量变量
补充资料：变质量体运动
