So when two boxes are connected together, and force is applied, two boxes move with the same acceleration. (assuming force is constant.) My question is, how are forces between two boxes get cancelled out? When force is applied to the first box, it would exert force into the second box which pushes the first box with the same reaction force... And I am not sure afterawards.
"By connected together" I mean that two boxes are stick together literally. There's no string or something like that. It's basically glued together.