Friction Calculator
This friction calculator finds the friction force from mass, coefficient and slope: a 10 kg body with μ = 0.3 on flat ground has F = 0.3 × 10 × 9.81 ≈ 29.4 N. On an incline the downhill force comes in as well.
Example: Mass 10 kg · Coefficient of friction μ 0.3 · Slope angle 20 ° → Friction force: Friction force F = 27.65 N. Source: Wikipedia – Reibung (Coulombsches Reibungsgesetz). Updated: .
How it is calculated
The friction force is the product of the coefficient of friction and the normal force: F = μ · N. The normal force is the force with which the body presses perpendicular onto the surface. On flat ground it equals the weight m · g.
Static and kinetic friction
While a body is at rest, static friction pushes back up to a maximum of μ · N. Once it slides, the usually slightly smaller kinetic friction acts. The calculator uses the coefficient you enter for both: it shows when the body starts to slide and then gives the acceleration. According to Coulomb's law the contact area does not matter.
Inclined plane
On a slope with angle α the weight splits into the normal force N = m · g · cos α and the downhill force m · g · sin α. The body slides when the downhill force exceeds μ · N, that is beyond the critical angle arctan μ. The pulling force uphill at constant speed is the downhill force plus friction.
- Typical coefficients range from about 0.05 (lubricated) to 1 (rubber on asphalt).
- With an angle of 0 the calculator works on the flat surface.
- The acceleration due to gravity is 9.80665 m/s².
Frequently asked questions
How do you calculate the force of friction?
F = μ · N, with coefficient of friction μ and normal force N. On flat ground N = m · g. For 10 kg and μ = 0.3 that is about 29.4 N.
What is the difference between static and kinetic friction?
Static friction holds a resting body in place and is larger; kinetic friction acts on a sliding body. Both follow F = μ · N, just with different coefficients.
At what angle does a body slide down a slope?
Beyond the critical angle where tan α = μ. For μ = 0.5 that is about 26.6°, independent of mass.
Sources and legal basis
- Wikipedia – Reibung (Coulombsches Reibungsgesetz)
- Wikipedia – Friction (Coulomb friction, angle of repose)
- Wikipedia – Schiefe Ebene
- BIPM – SI-Broschüre: Normfallbeschleunigung g_n = 9,80665 m/s²
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