根据牛顿运动第三定律，作用力和反作用力是大小相等方向相反的。

According to Newton's Third Law of Motion action and reaction are equal and opposite.

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每一个作用力都会引起相等的和相反的反作用力。

For every action there's an equal and opposite reaction.

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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.

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