Constant used in Friction?

Question

HEy whats a constant used in calculating friction?

Answer 1

The friction coefficient (k). This is usually found through experimentation because a lot of factors go into determining what the value of k might be. For example, with the same materials involved k varies according to if the sliding body is stationary or actually moving and whether it is sliding or rolling when it does move.

But k also varies with the materials of the sliding body and the thing the body is sliding (or rotating) on. For example, k would be way higher for something sliding on sand paper than on ice.

Anyway, the friction force equation is F = kmg cos(theta); where theta is the angle of the ramp the body is sliding or rolling on, mg = W the weight of the sliding/rolling body of mass m, and k is that not so constant constant.

(NB: Finding k for a block/ramp combination is relatively easy to do. It is often done in HS physics labs.)

Answer 2

It is called "u" and it is involved in the formula "Force due to friction=Normal Force of the object times the constant u".