# Newton's Third Law

Suppose there are two point particles A and B. They move away from each other due to their mutual interaction.

According to Einstein, there is no absolute space; so there is only relative motion between the two. In a way, I think we cannot even speak about which particle is moving away from the other. In this context, what does the Conservation of Momentum, or alternatively Newton's third law mean? How does it fit into all this?

• I'm not sure I understand the question - what has the fact that the motion might look different in different frames to do with conservation of momentum? Commented Apr 28, 2017 at 11:06
• Newton's III law has to do with accelerations of two point mass (there is interaction between them), and the accelerations are proportional to each other. Relative motion is quite different here -- in your context, you are referring to uniform motion (no acceleration) seemingly. Commented Apr 28, 2017 at 13:05
• @ACuriousMind That's what am asking. Commented Apr 29, 2017 at 10:29
• @PhyEnthusiast would you mind accepting the answer or else comment what is missing from the answer? Commented May 1, 2017 at 11:49