只有一种反作用力，那就是你，山姆大叔。
Only one counterforce was available, and that was you, Uncle Sam.
其反作用力F’为物块对人施加的力。
The reaction is the force F'exerted by the block on the man.
作用与反作用力大小相等，方向相反。
Example 4:Action is equal to reaction, but it acts in a contrary direction.
还有一个例子证明作用力,与负反作用力相等。
That's another example where you see action equals minus reaction.
每一种作用力都有一种与之等量的反作用力。
Every kind of input strength has a reverse strength which is as big as it.
因为根据牛顿定律，每个动作都有反作用力。
Because according to Newton, for every action there's an opposite reaction.
第三个定律说每一个作用力都有相等的反作用力。
The third law said that every action has an equal and opposite reaction.
从物理中我们知道每个作用力都有它的反作用力。
From physics we know that for every action there is an opposite reaction.
这个作用力所产生的反作用力推动宇宙飞船前进。
The reaction force to this action force pushes rocket ship along.
也许用玩具气球的情况最容易说明这种反作用力。
It is perhaps easiest to understand the reaction in the case of the toy balloon.
每一个作用力都会引起相等的和相反的反作用力。
其包含了三种情况：作用力与反作用力都不做功；
It contains three situations: both of force and reaction do not work;
任何事物都处在一对相反作用力之下，且处于平衡状态。
Everything is in a pair of opposite forces and in a state of equilibrium.
每一个作用力都有一个大小相等、方向相反的反作用力。
作用于物体上的力会受到大小相等、方向相反的反作用力。
A force which ACTS on an object is opposed by an equal and opposite reaction.
除了某特别情况之外，所有动作应以一个向后的反作用力作开始。
All movements must begin with a backward motion with a very few exceptions.
一个物体对另一个物体施加力，从来不会不受到后者的反作用力。
One body never exerts a force on another without the second reaction against the first.
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.
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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