Friction Calculator
Calculate the friction force from the normal force and coefficient of friction.
Dimensionless. Use μs for static or μk for kinetic friction.
Friction Force (F_f)
Normal Force Used (N)
The F = μN Model
The force of dry friction between two surfaces is modeled as the product of a dimensionless coefficient of friction (μ) and the normal force (N) pressing the surfaces together: F_f = μ · N. On a flat, level surface with no other vertical forces, the normal force equals the object's weight, N = m · g.
- F_f - Friction force (N)
- μ - Coefficient of friction (dimensionless)
- N - Normal force (N)
- m - Mass (kg), g - Gravity (≈ 9.81 m/s²)
Static vs Kinetic Friction
Static friction (μs) resists the start of motion and can vary from zero up to a maximum value of μs · N. Kinetic friction (μk) acts on an object already sliding and is usually smaller than the maximum static friction, which is why it takes more force to start an object moving than to keep it moving.
Typical Coefficient Values
Coefficients depend strongly on the materials and surface conditions. The values below are approximate and for reference only.
| Material Pair | Static (μs) | Kinetic (μk) |
|---|---|---|
| Rubber on concrete (dry) | 1.0 | 0.8 |
| Steel on steel (dry) | 0.74 | 0.57 |
| Wood on wood | 0.4 | 0.3 |
| Glass on glass | 0.94 | 0.4 |
| Ice on ice | 0.1 | 0.03 |
Related Calculators
Note: This calculator uses the idealized dry-friction model F = μN and assumes a level surface when deriving the normal force from mass. Real coefficients vary with surface condition, temperature, and contamination. Results are for educational purposes.