Friction resists sliding between surfaces. Static friction holds things in place up to a limit; kinetic friction acts once they slide. Tyres, brakes, shoes and screws all rely on it.
How to use the Friction Calculator
- Friction coefficient μ
- Normal force from…
- Normal force N
- Mass
- Surface angle
- Gravitational acceleration g
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the friction coefficient and either the normal force or the mass and slope angle. Typical values: rubber on dry asphalt 0.7–0.9, steel on steel 0.6 (dry) or 0.1 (lubricated), ice on ice 0.03.
Tips
- Pick a positive direction (usually up or forward) and keep the signs consistent.
- Every field has its own unit menu – mix km/h, m/s and mph freely.
- The equations of motion assume constant acceleration; split a journey into stages if it changes.
- Air resistance is ignored unless the calculator asks for drag.
Common mistakes to avoid
- Using a speed in km/h in a formula that needs m/s.
- Treating g as positive in one equation and negative in another.
- Confusing distance travelled with displacement.
Inputs explained
| Field | What to enter |
|---|---|
| Friction coefficient μ | A number |
| Normal force from… | Choose one: Enter the normal force, Mass on a surface |
| Normal force N | Units: N, kN, MN, mN, lbf, kgf … |
| Mass | Units: kg, g, mg, t, lb, oz |
| Surface angle | Units: °, rad, arcmin, arcsec, mrad |
| Gravitational acceleration g | Units: m/s², ft/s², g, cm/s² |
What each result means
- Friction force = [Friction coefficient μ]×[Normal force]
- Angle at which an object starts sliding (static) = deg(atan([Friction coefficient μ]))
Example values
How the main result changes when Friction coefficient μ changes and everything else stays at the example values above:
| Friction coefficient μ | Friction force (N) |
|---|---|
| 0.3 | 150 |
| 0.45 | 225 |
| 0.6 | 300 |
| 0.75 | 375 |
| 0.9 | 450 |
| 1.2 | 600 |
Formula
F = μ × N, N = m·g·cos θ on an inclineWorked example
Inputs — Friction coefficient μ: 0.6; Normal force from…: Enter the normal force; Normal force N: 500 N; Gravitational acceleration g: 9.80665 m/s².
Results — Normal force = 500 N; Friction force = 300 N; Angle at which an object starts sliding (static) = 30.96 °.
Key terms
- Normal force
- The force perpendicular to the contact surface.
Frequently asked questions
What is the difference between static and kinetic friction?
Static friction prevents sliding up to a maximum; kinetic friction acts while sliding and is usually smaller.
Does friction depend on contact area?
For dry solid surfaces, approximately not.
Can μ be greater than 1?
Yes – racing tyres and rubber on rough surfaces can exceed 1.
What is the angle of repose?
arctan(μs), the steepest slope on which an object stays put.
What formula does the Friction Calculator use?
F = μ × N, N = m·g·cos θ on an incline.