Does a rougher surface cause more friction?
Yes, because the co-efficient friction is larger. The formula for friction is: F= μR, where μ is the co-efficient of friction, F is friction and R is the reaction force pushing up on the object on the surface. (If the object is resting upon a horizontal surface, then R is equal to the weight of the object, i.e. mass * gravitational field strength). If you increase μ, F increases. So, the friction is larger. The co-efficient of friction is actually dependant upon the smoothness/roughness of a surface. EDIT: eyeonthescreen, I have put exactly what you have put, except I actually wrote it myself… Plus you have written that k increases but everything stays the same. How is that possible? If F is proportional to k, then F increases as k increases! So your last paragraph is non-sense.
