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Friction Coefficient & Normal Force

Calculate μN for kinetic friction or a maximum static-friction estimate using a supplied coefficient.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

With coefficient 0.3 and normal force 200 N, μN is 60 N. For static friction, that is a limiting value; the actual static force can be smaller.

Kinetic friction magnitude = μkN; maximum static friction magnitude = μsN

Worked example

Enter these known values and leave the other values blank.

Selected friction coefficient
0.3
Normal contact force
200 N
Friction magnitude / static limit
60 N

Assumptions and limitations

  • Use a coefficient appropriate to the surfaces and conditions. Kinetic and static coefficients are different inputs and are not selected automatically.
  • For a sliding contact, the simple model gives kinetic friction magnitude. For static contact, μsN gives only the maximum; actual static friction adjusts up to that limit.
  • The coefficient, normal force and friction magnitude must be nonnegative. Coefficients are not universally bounded by 1.
  • The normal force is perpendicular to the contact surface and is not automatically equal to weight. The tool returns magnitude, not a force direction.

Common questions

Why is actual static friction sometimes below μN?

Static friction supplies the force needed to prevent slipping, up to its limiting value. A smaller tangential demand produces a smaller actual static-friction force.

Can I recover the coefficient?

Enter a positive normal force and the relevant friction magnitude or measured static limit. The quotient F/N is the corresponding model coefficient.

References

The pound-force uses the exact international pound and standard gravity instead of the rounded captured factor.

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