Physical laws govern relatively simple systems. A human being is a vastly more complex system, with a huge number of physical laws coming into play with even the simplest of interactions. Thus, you shouldn't try to apply action/reaction in this area.
If I bump into something, my mental reaction is the result of a huge number of factors, including how I perceive the event, my state of mind and my history with regards to those events. Each of those in turn is hideously complex, and if you do arrive at basic physical laws, it will be at a much lower level than what presents itself to me (and you'd end up with a huge amount of them).
This fallacy is all too common. Many people try to apply scientific concepts to Buddhist ones, and it's a mistake. Newton's laws don't give you ready predictions for human behavior, conservation of energy does not support rebirth, etc...
If you are really interested in studying this, I recommend studying scientific laws on their own, then moving up to complex systems, and emergence. If nothing else, it will give you an idea of what a gross oversimplification people make when they make this mistake.