A concept I don't understand is the force exerted by one block of mass m1 on a block of mass m2 and vice versa when a force F is applied to m1. What I mean is, say you have to blocks next to each other and a force F is applied to m1. My physics teacher says m1 will accelerate, but m2 will accelerate in the opposite direction. How can the forces be equal if m1 and m2 aren't? My teacher says F - (m2)(a) = (m1)(a). How is this possible? It makes absolutely no sense to me how this can be possible if (m2)(a) and (m1)(a) form an action-reaction pair.