I know that normal force is a reaction force. http://www.sumoware.com/images/temp/xzhhpaacgkdktjna.png [Broken] In the leaning ladder problem, the normal force is perpendicular to the floor and the wall. But, in the cable and beam problem, why isn't the normal force perpendicular to the wall ? http://www.sumoware.com/images/temp/xzeanhxxmcalmnkn.png [Broken] Hmm.. Then, I imagine what the system (cable and beam) will be without the wall. I think that the beam will fall down. And, because the beam touches the wall, the wall will exert a force back to the beam at right direction. So, the normal force will have up and right direction. But, I imagine the ladder problem. But, Why the N1 doesn't have the upward direction ? I think if there is no wall, then the ladder must fall and rotate counter-clockwise. Please explain me how to determine the normal force direction.