Hello, I am returning to college after a ten year hiatus and am taking an online course on edx to try and refresh my knowledge a bit before the fall. I read a few other posts on Newton's Third law, but it seems I am falling short on this one concept. In the case of an object, m_1, which is at rest on some frictionless table. There is a rope connecting this object to another object, m_2, which is hanging over the edge. To be clear, the rope connects m_1 to m_2, m_1 is on the table and m_2 hangs in the air off the edge of the table. There could be a pulley if you like on the edge of the table assisting with the direction change of the rope. Assume I am drawing the free body diagrams for m_1 and m_2 separately, *not* as a single system. Also for simplifying explanation, assume a cartesian coordinate system with +y in the vertical at 90 and -y at 270, and +x at 0 and -x at 180. I place a downward arrow on each diagram for the F_mg. In the case of m_1, I have a opposite Normal force with an upward arrow and an arrow in the +x direction for the tension force on m_1 by the rope. It makes sense to me that the Normal force in this case is opposing the gravitational force. Why is it correct that m_2 only has the downward F_mg force (as mentioned) and an upward T force on m_2 from the rope? Why is the normal force not included here? As it stands, I am just "playing along" that the force just needs something to oppose it, so we have the Normal force and with m_2, the Tension force is sufficient, but I don't really understand. Is the Normal force only present in cases where there needs to be a "mathematical correction" and could any other provide the opposing force? What if there was a person pushing down on a box? There would be the arrow downward for F_mg, and would the applied contact force be sufficient as an opposing force where as there would be no normal force? Thanks in advance!