Friction Force Calculator (Static and Kinetic)
Enter the mass, the friction coefficients and the slope angle (0 for flat).
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Friction Force Calculator (Static and Kinetic) by TheCalcTools
How the Friction Force Calculator (Static and Kinetic) works
Friction is proportional to the normal force pressing the surfaces together: static friction up to μsN stops an object starting to move; kinetic friction μkN resists it once sliding. On a slope N = mg cos θ.
An object slides down a slope on its own when tan θ is greater than μs, the friction angle.
The formula
Worked example
Using the default values shown in the calculator:
| Mass (kg) | 20 |
|---|---|
| Static coefficient μs | 0.5 |
| Kinetic coefficient μk | 0.4 |
| Slope angle (degrees) | 20 |
- A 20 kg box on a 20° slope: normal force 184.30 N, maximum static friction 92.15 N.
- Gravity pulls it down the slope with 67.08 N: No: static friction holds it.
Result:
| Normal force (N) | 184.30 |
|---|---|
| Maximum static friction (N) | 92.15 |
| Kinetic friction while sliding (N) | 73.72 |
| Force down the slope (N) | 67.08 |
| Does it slide on its own? | No: static friction holds it |
| Steepest slope before sliding (degrees) | 26.57 |
Frequently asked questions
Why is kinetic friction lower than static?
Once moving, the microscopic contact points have less time to bond, so the resistance drops.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.