Free · Kinematics calculators — How things move ⏱️

Friction, Normal Force & Coefficient

Relate sliding friction or limiting static friction to normal force and a nonnegative friction coefficient.

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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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Formula and method

A friction magnitude of 30 N under a 100 N normal load gives a coefficient of 0.3. At the same normal load, a zero coefficient gives zero friction.

Friction magnitude = coefficient × normal force

Worked example

Enter these known values and leave the other values blank.

Normal force magnitude
100 N
Sliding or limiting friction magnitude
30 N
Friction coefficient
0.3

Assumptions and limitations

  • Normal force is positive; coefficient and friction magnitude are nonnegative. The coefficient is dimensionless and is not universally bounded by one.
  • Use kinetic friction for steady sliding or maximum static friction at impending slip. Below impending slip, actual static friction can be smaller than μsN, so this equality cannot identify μs from an arbitrary static force.
  • This is the simple dry-friction model. Surface condition, speed, lubrication and temperature can change measured friction. Zero friction and zero coefficient do not uniquely determine the normal force.

Common questions

Does a stationary object always experience μN of friction?

No. Static friction adjusts to the applied tangential load up to its limit. Use the limiting value to infer a static friction coefficient.

Can a friction coefficient exceed one?

Yes. This model accepts nonnegative coefficients without imposing an upper limit of one.

References

Bookify requires positive normal force and nonnegative friction magnitude and coefficient. The pound-force uses the exact international pound and standard gravity instead of the rounded captured factor.

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