利用作用力做功和反作用力做功的代数和与参照系的选择无关这样的结论，计算质点组的内力作功之和将非常简捷方便。

The sum of work of effect and reaction has nothing to do with the choice of criterion. With this conclusion, it is very easy to work out the sum of particle and work of internal force.

youdao

So, what we're looking at here is the force when we have two charged particles, one positive one negative -- here, the nucleus and an electron.

我们现在研究的是,一正一负俩个带电粒子之间的,作用力-在这里。

麻省理工公开课 - 化学原理课程节选

But you can also look at it qualitatively, so, if you think about the force between the electron and the proton, you could just qualitatively think about what's happening.

但你也可以定性的来研究这个问题，所以如果你们考虑电子,和质子之间的作用力,你可以定性的来想。

麻省理工公开课 - 化学原理课程节选

If nothing is touching the body, there are no forces on it, with one exception which is, of course, gravity.

如果没有实体接触,那么它就不受作用力,当然一个例外那就是引力

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