Heres a simple situation I can't seem to adequately explain to students. A box experiences a force exerted on it by the earth. The third law of newton states that an object that feels a force exerts an equal and opposite force, which is the force that the box exerts onto the earth. If the box and the earth are now in contact, is the force exerted by the box onto the earth the normal force? I'm thinking that it's a very unique force that pertains to two masses glued together. Can somebody share their ideas on normal force? Thanks!