Friction Force Calculator

How it works

1. 1Enter the coefficient of friction µ — use the static value for the maximum holding force, or the kinetic value for a sliding surface.
2. 2Enter the normal force N acting perpendicular to the surface in your chosen unit system (N or lbf).
3. 3The calculator applies F = µ·N and returns the friction force, converted back to your selected unit.

Use cases

• Mechanical design — determine whether a clamped or bolted joint will resist sliding under a load.
• Vehicle dynamics — estimate braking or traction forces for a known axle load and tyre–road coefficient.
• Physics coursework — explore how varying µ or N affects the resulting friction force.

Frequently asked questions

What is the formula for friction force?

Friction force is F = µ·N, where µ is the dimensionless coefficient of friction and N is the normal force in newtons. For example, with µ = 0.3 and N = 100 N the friction force is 0.3 × 100 = 30 N.

How do I find the normal force on a flat surface?

On a horizontal flat surface the normal force equals the weight: N = m·g. For a 10 kg object, N = 10 × 9.81 = 98.1 N. On an inclined surface, N = m·g·cosθ.

What is the difference between static and kinetic friction coefficients?

The static coefficient µs applies before motion and is usually higher than the kinetic coefficient µk, which applies once sliding begins. Use µs for the maximum force before motion starts, and µk for the ongoing friction during motion.