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.

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.

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.