Question

how does the roughness of a surface affort friction

Answer 1

The resistance offered by friction depends directly on the force applied to move the two surfaces and the roughness of the surfaces. The smoother the surfaces, the less the resistance; the rougher the surface, the more the resistance.

Answer 2

If the surface is rough so there will be more friction while if the surface is smooth there will be less friction..
Eg: if a ball is rolling down from a smooth surface it will roll faster as there is less friction but if the same ball is rolling down on a rough surface it will roll slowly as there will be more friction..