Back to basics with this question but I really want to make sure I understand this concept.

Newton's third law states that 'every action has an opposite and equal reaction', which we can see through interaction pairs. However, I'm a little confused on what is happening. I read the answer to 'With Newton's third law, why are things capable of moving?' by Andrew C, however in his diagram, he had a force called F matchbox, and I was just wondering shouldn't the matchbox counteract this force through the interaction pair that it forms?

I find it helpful to visualise concepts, and so basically I have come up with this little thought experiment but I wasn't exactly sure if it's the right way to look at things. Essentially, I imagine a man jumping, and visualise the force the man is exerting on the Earth. I then imagine how silly it would be that the Earth itself moved because of this force, however I then see that the man has risen in the air due to the reaction force. In this way I was able to explain why interaction pairs, even though they are balanced could lead to movement and acceleration.

BTW I realise that a similar question may have been asked before, but the answers I have seen just don't fully explain what's going on and I don't have enough reputation to comment. :(


The third law says "if body A exerts a force on body B, body B exerts and equal and opposite (direction) force on body A. In terms of causing motion, these forces do not cancel. If we are evaluating the motion of body A, we include all the forces acting on body A, and this includes the force body B exerts on A, but not the force that body A exerts on B. The force that body A exerts on body B does not figure in determining the motion of body A. It only figures in determining the motion of body B.


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