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?

Edited April 25, 201411 yr by DirectionofTime

Friction is kinetic when the book slides and static when it is at rest. The railings might not be having a uniform friction coefficient. It has to do with forces that arise due to molecular interactions. If you make the surface perfectly clean, not a single speck of dust, friction coefficient becomes very large as molecular associations become stronger.