If I push a box forward, then probably, the force I apply can be considered external force acting on the system of particles of the box. In rigid bodies like the box, each particle of the body should experience some force and as a result of the interaction of applied force with each particle of the body there is a net external force which will move the object forward. (Do correct me if I'm wrong.)
But I kept wondering that if I'm applying the force to certain portion of the box then the forces will be experienced only by the particles directly in contact with my hands. Then how does other particles of the rigid object experience force? Is it related to intermolecular forces?