What is the coefficient of friction?

The coefficient of friction (μ) is a dimensionless number that describes how much resistive force exists between two surfaces. It is defined by the ratio μ = F / N, where F is the friction force and N is the normal force pressing the surfaces together. Higher values mean more friction.

What is the difference between static and kinetic friction?

Static friction (μs) acts on a stationary object and must be overcome to start motion. Kinetic friction (μk) acts on an already-moving object. The static coefficient is almost always larger than the kinetic coefficient for the same surface pair, which is why it takes more force to start something sliding than to keep it sliding.

What are typical coefficient of friction values?

Values vary widely: ice on ice is very low (μk ≈ 0.03), rubber on dry concrete is high (μk ≈ 0.80), steel on steel falls in between (μk ≈ 0.42–0.57), and Teflon on steel is extremely low (μk ≈ 0.04). See the reference table on this page for a broader list.

How is normal force related to weight?

On a flat horizontal surface, the normal force equals the object's weight: N = m × g, where g ≈ 9.81 m/s². On an inclined plane at angle θ from horizontal, the normal force is N = m × g × cos(θ). Use the calculated N as your input to find the friction force.

Can the coefficient of friction be greater than 1?

Yes. While many everyday surfaces have μ 1. There is no theoretical upper limit; the value simply reflects how "grippy" the surfaces are relative to the normal force.

Does friction depend on contact area?

In the classical Amontons-Coulomb model — the one this calculator uses — friction does not depend on the area of contact, only on the normal force and the coefficient μ. This is a good approximation for most rigid solid surfaces under everyday conditions.

Coefficient Of Friction Calculator

Calculate the coefficient of friction (static or kinetic), friction force, or normal force — select your unknown, enter two known values, and get the answer instantly.

Friction Type

Choose static (before motion begins) or kinetic (during sliding).

Solve for

Select the unknown variable, then enter the two known values.

F = μs × N

Coefficient of Friction (μs) (dimensionless)

Must be ≥ 0. Typical range: 0.01 – 1.5

Normal Force (N) (Newtons)

On flat surface: mass (kg) × 9.81

Result

Enter values on the left and click Calculate.

Common Friction Coefficients

Click a row to use that coefficient value in the calculator.

Surface Pair	μs	μk

Values are approximate and vary with surface condition, temperature, and lubrication.

Summary

The Coefficient of Friction Calculator solves the standard friction equation F = μ × N for any one of its three variables — coefficient of friction (μ), friction force (F), or normal force (N). It supports both static friction (the force needed to start motion) and kinetic friction (the force opposing ongoing sliding). Enter any two known values, select the unknown, and the result appears instantly. A built-in material reference table lists typical static and kinetic coefficients for common surface pairs.

How it works

Choose the friction type: Static (prevents motion) or Kinetic (opposes ongoing motion).
Select what you want to solve: Coefficient (μ), Friction Force (F), or Normal Force (N).
Enter the two known values in the input fields.
Click Calculate — the tool applies F = μ × N (rearranged as needed) and displays the result.
Optionally click any row in the reference table to pre-fill the coefficient field.

Use cases

Physics homework: find the coefficient of friction from measured force and weight data.
Engineering: determine whether a part will slide or remain stationary under a given load.
Automotive: estimate braking and tire-grip coefficients for different road conditions.
Manufacturing: calculate the friction force needed to move a workpiece on a conveyor surface.
Lab experiments: back-calculate μ from two measured quantities.
Safety checks: verify whether a surface coating provides sufficient friction to prevent slipping.
Inclined plane problems: combine with the normal force component (mg cos θ) to find friction.
Material selection: compare static vs. kinetic coefficients when designing joints or slides.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu