How this calculator works
For a sliding contact, the simple Coulomb model multiplies the kinetic coefficient by normal force. For a static contact, the same product is a limit; actual friction adjusts to the applied load until slipping begins. Normal force acts perpendicular to the contact and need not equal weight. Coefficients are nonnegative and can exceed one. A zero known factor cannot determine the other factor in an inverse calculation.
Formula
F_k = mu_k N; F_s <= mu_s N; mu = F/N; N = F/mu.
Worked example
A coefficient of 0.2 and normal force of 100 N give 20 N of kinetic friction, or a 20 N static limit if the coefficient is static.
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Frequently asked questions
Is static friction always mu times N?
No. That value is the maximum before slipping. Below the limit, static friction balances the required tangential load.
Should I use mass as normal force?
No. Convert mass to weight and account for the contact geometry and other vertical forces.
Can a coefficient be larger than one?
Yes. One is not a universal upper bound for a measured contact coefficient.