Friction Calculator
Use our friction calculator to calculate friction force from coefficient of friction (μ) and normal force (N). Includes the friction formula in physics, what friction is in physics, and how to calculate friction (plus notes on finding μ and cases without a coefficient).
What Is Friction in Physics?
Friction is a force that resists relative motion (or the tendency of motion) between two surfaces in contact. In physics problems, friction often acts opposite the direction of motion along the surface.
A common simplified model uses a friction coefficient (μ) and the normal force (N) to estimate the friction force. This is widely used in introductory mechanics for sliding objects, blocks on ramps, and motion with surfaces.
This friction calculator uses the standard relationship F = μN.
Friction Formula
In the basic model, friction force equals the coefficient of friction times the normal force.
F is the friction force, μ is the friction coefficient, and N is the normal force.
Use this to calculate friction coefficient if you know F and N.
A straightforward friction calculation.
How to Calculate Friction Force
- 1
Enter the coefficient of friction (μ).
- 2
Enter the normal force (N).
- 3
The calculator returns the friction force using F = μ · N.
Frequently Asked Questions
Friction is a contact force that opposes relative motion (or impending motion) between surfaces. It acts along the surface and typically opposes sliding.
A common model is F = μN, where μ is the coefficient of friction and N is the normal force.
Rearrange the formula: μ = F/N, using the measured friction force F and normal force N.
If friction is the only horizontal force causing acceleration (or deceleration), you can use Newton’s second law: F = m·a. Then you can find μ by μ = F/N. On a flat surface with no vertical acceleration, N ≈ m·g.
You can’t use F = μN without μ. Instead, you’d need other information—like measured acceleration (F = m·a), a force balance from a free-body diagram, or experimental data—to determine the friction force directly.
Not always. Static friction can vary up to a maximum (often modeled as Fs ≤ μsN), while kinetic friction during sliding is often modeled as Fk = μkN. This calculator uses the common simplified magnitude relationship.