This has always puzzled me, the normal force, and I think I might understand this now, or at least part's of it. So here's the case: there's a plank of wood leaning against a wall. If it's not slipping/sliding or any of the sort, then there is no movement in the x or y direction. Then, there must be a normal force from the floor holding it up. There must also be a normal force on the side that keeps it from falling. That get's tricky here for me. So, if it was perfectly balanced and not leaning on anything, then the normal force would just be equal to MG in the y-direction. Now, if it is leaning on a wall, then the normal force coming from the wall would be only in the x direction. Thus, the horizontal normal force should not affect the vertical one. So, the normal force from the ground must also be equal to MG in this case. I'm also learning about angular momentum right now. So, would the horizontal normal force be just a torque such that it prevents it from rotating down? Now, uncertain territory begins: Suppose the plank began to slide without friction. The vertical normal force would then be a constant right? And the horizontal normal force would change? But there is one little problem. I've always noticed that my hockey stick (i.e a plank of wood) always seem to make a big bang sound as though the whole stick hit the floor and not just one edge. So, does that mean that at some point, it loses contact with the wall?