Kinetic Friction Calculator
Calculate the kinetic friction force on a sliding object using its friction coefficient and normal force.
How it works
- 1Enter the coefficient of kinetic friction (μk) — typical values range from 0.1 (ice on ice) to 0.8 (rubber on concrete).
- 2Enter the normal force N pressing the object against the surface. Select metric (N) or imperial (lbf).
- 3The calculator applies F_k = μk·N and shows the resisting friction force opposing the motion.
Use cases
- Mechanical engineers sizing motors or brakes that must overcome friction while an object moves.
- Physics students verifying lab measurements of sliding friction on inclines or flat surfaces.
- Automotive engineers estimating tyre friction during braking or cornering on a road surface.
Frequently asked questions
What is the formula for kinetic friction force?
F_k = μk·N, where μk is the coefficient of kinetic friction and N is the normal force in newtons. For example, if μk = 0.4 and N = 100 N, the kinetic friction force is 0.4 × 100 = 40 N.
Why is kinetic friction usually less than maximum static friction?
Static friction can build up to F_s,max = µs·N before motion begins, and µs is typically 10–30% higher than µk. Once sliding starts, the microscopic contact decreases slightly, so the force drops to the lower, roughly constant kinetic value.
Is kinetic friction truly constant while sliding?
In the classic model, yes — F_k = μk·N is independent of speed and contact area. In practice μk varies slightly with velocity and temperature, but the constant-coefficient model is accurate for most problems.
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