Quick answer
The friction force is f = μN. A coefficient of 0.3 and a normal force of 100 N give 30 N.
Enter the coefficient of friction and the normal force. The calculator returns the friction force.
Related tools: Force Calculator: Force from mass and acceleration (Newton's second law). Centripetal Force Calculator: Force and acceleration for circular motion. Normal Force Calculator: Normal force on an object resting on a flat or inclined surface.
How to use the Friction Force Calculator
- Enter coefficient of friction μ (0 or more).
- Enter normal force (N) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Coefficient of friction μ | A number | ≥ 0 |
| Normal force | A number, in N | > 0 |
Formula and method
Formula
f = μ N
IEEE-754 double precision; shown to the decimals indicated.
Use the static coefficient for the maximum force before sliding, kinetic while sliding.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Coefficient of friction μ = 0.3; Normal force = 100.
| Result | Value |
|---|---|
| Friction force | 30 N |
Example 2
Inputs: Coefficient of friction μ = 0.05; Normal force = 2500.
| Result | Value |
|---|---|
| Friction force | 125 N |
Example 3
Inputs: Coefficient of friction μ = 0.8; Normal force = 49.03.
| Result | Value |
|---|---|
| Friction force | 39.224 N |
The first line is the headline result (friction force). IEEE-754 double precision; shown to the decimals indicated.
Worked example
A 10 kg box on a flat floor has N = 98.07 N, and with μ = 0.3 the friction force is 29.4 N. To move it, you must push with more than that (using static μ).
Where this estimate stops applying
The coefficient is dimensionless and depends on the surfaces. Friction is independent of contact area in the basic model. On a slope the normal force is mg cos θ.
How the result changes with coefficient of friction μ
Holding every other input at the first worked example, this table changes only coefficient of friction μ. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Coefficient of friction μ | Friction force |
|---|---|
| 0.15 | 15 N |
| 0.3 | 30 N |
| 0.6 | 60 N |
| 1.2 | 120 N |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Coefficient of friction μ: entering "-1" shows "Coefficient of friction μ must be at least 0." beside that field and no result.
- Normal force: entering "0" shows "Normal force must be greater than 0." beside that field and no result.
Choosing between the Friction Force Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Force Calculator](/science/force-calculator/) | mass and acceleration | Force |
| [Centripetal Force Calculator](/science/centripetal-force-calculator/) | mass, speed and radius | Centripetal force |
| [Normal Force Calculator](/science/normal-force/) | mass, incline angle and gravitational acceleration | Normal force |
| [Net Force Calculator](/science/net-force-calculator/) | force magnitudes and direction of each force | Net force |
| [Coefficient of Friction Calculator](/science/coefficient-of-friction-calculator/) | friction force and normal force | Coefficient of friction |
Background: motion and mechanics
For constant acceleration the standard relations are v = u + at, s = ut + ½at², v² = u² + 2as and s = ½(u + v)t. Pick the equation that contains your three known quantities and the one you want. Use SI units (metres, seconds, kilograms, newtons, joules) throughout or the answer will be off by a factor.
These equations stop applying when acceleration changes during the motion, as with a rocket burning fuel; that needs calculus or numerical methods.
Assumptions and limitations
- μ is dimensionless
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for coefficient of friction μ and normal force to confirm this.
Frequently asked questions
Does friction depend on speed?
Slightly, but the model treats it as constant.
What is the normal force on a flat surface?
The object's weight.
What's the difference from the coefficient calculator?
That page finds μ from a friction and normal force; this one multiplies a known μ by N to get the force.
What does the Friction Force Calculator calculate?
Friction force from the coefficient of friction and the normal force. It returns Friction force.
What formula does the Friction Force Calculator use?
f = μ N. Use the static coefficient for the maximum force before sliding, kinetic while sliding.
What do I need to enter in the friction Force Calculator?
You enter Coefficient of friction μ and Normal force (N).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. μ is dimensionless.
What is an example of a friction Force result?
With coefficient of friction μ 0.3 and normal force 100, the friction force is 30 N.
Related calculators
- Force Calculator — Force from mass and acceleration (Newton's second law).
- Centripetal Force Calculator — Force and acceleration for circular motion.
- Normal Force Calculator — Normal force on an object resting on a flat or inclined surface.
- Net Force Calculator — Resultant of several forces at different angles.
- Coefficient of Friction Calculator — Coefficient of friction from friction and normal forces.
- Momentum Calculator — Linear momentum from mass and velocity.
Sources
- OpenStax, University Physics Volume 1 (Rice University): mechanics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.