action and reaction force

Action and reaction are described by Newton's Third Law. It says:" For every action, there is an equal (in magnitude) and opposite (in direction) reaction."

Notice that action and reaction forces act on different bodies, they do not act on the same body.

In a rocket launch, the hot gas produced in the rocket engine is expelled out at the tail of the rocket, this is an action force which forces the gas out. The reaction force, that is equal in magnitude but opposite in direction, pushes the rocket to lift up.

Hence, the action force acts on the exhausted gas, whereas the reaction force acts on the rocket.

更加簡單例子，你可以企係地面上，係因為地面有一個相同你體重但向上嘅反作用力，如果你唔信你可以試試企係水面上。