As a sort of experiment, I let my physics textbook slide down two railings. The first railing was a very rough surface, and the physics textbook would only slide about a quarter of the way down and then stop. I then took my physics book and slid it down another railing. This railing was a smooth surface, but about the same height, and it slid all the way down in I would estimate ~2.0 s. Now, I know this has to do with static frictional forces. What I’m curious about is why did this happen, in detail? Does it have to do with the structure of the surfaces at the molecular level?