Coulomb Friction Force and Coefficient

Content

Solve the dry Coulomb friction relation for friction-force magnitude, coefficient of friction, or normal load, with force-unit conversion and clear static-limit interpretation.

Inputs

Result

Friction force
32.5N

Kinetic friction magnitude during sliding; the friction vector opposes relative sliding.

Friction force32.5 N
Normal load250 N
Coefficient μ0.13
ConditionKinetic sliding

Use magnitudes only. Direction is not solved: friction acts opposite impending motion or relative sliding.

How to use

  1. Select Friction force, Coefficient, or Normal load as the unknown.
  2. Choose kinetic sliding or maximum static friction. Enter the two required magnitudes and select each force unit.
  3. Select Calculate to update the single result panel. Select Reset to restore the kinetic example of N = 250 N and μ = 0.13.
  4. Read the canonical result first, then check the supporting values converted to newtons.
  5. Correct any red warning before use. A static result is a limiting value, not the actual self-adjusting static force below impending slip.
  6. Use a coefficient validated for the material pair, surface condition, environment, pressure, temperature, speed, and friction regime.
  7. Do not use this model where lubrication, adhesion, stick-slip, anisotropy, thermal effects, or speed-dependent behavior dominates.

Equations used

F = μN — friction-force magnitude or maximum static friction.
μ = F/N — dimensionless coefficient for N > 0.
N = F/μ — normal load for μ > 0.

Symbols and units: F is friction-force magnitude and N is positive compressive normal load; both use N, kN, lbf, or kgf. μ is dimensionless. Force conversion uses 1 kN = 1000 N, 1 lbf = 4.4482216152605 N, and 1 kgf = 9.80665 N.

Sign convention: entered values are non-negative magnitudes. The friction vector opposes impending or relative sliding. For static contact, 0 ≤ |fₛ| ≤ μₛN and this calculator reports the maximum static friction μₛN.

Assumptions and limits: constant Coulomb coefficient and positive compressive N. The model omits speed, temperature, nominal pressure, lubrication, running-in, adhesion, stick-slip, and directional dependence.