Friction Force Calculator
Enter the mass, coefficient of friction and surface angle to instantly find the friction force, normal force, net force and resulting acceleration using the standard F = μN model.
kg
Surface preset (μ)
°
F_friction = μ × N (opposing motion)
- 1
Weight
m × g = 10 × 9.807 = 98.066 - 2
Normal force (flat surface)
N = W = 98.066 = 98.066 - 3
Friction force
μ × N = 0.5 × 98.066 = 49.033
How does this calculator work?
Friction force is F = μN where N is the normal force pressing the surfaces together. On a flat surface N = mg; on a slope at angle θ, N = mg·cos θ. Enter mass, friction coefficient and angle to get the friction force, normal force, net force and acceleration. A negative net force means the object stays still.
Formula
How this is calculated
Friction is the force that opposes relative motion between surfaces in contact. The simplest model — Amontons-Coulomb friction — says the friction force is proportional to the normal force pressing the surfaces together: F = μN, where μ (the coefficient of kinetic friction) is a dimensionless constant that depends on the materials and surface condition.
For a flat horizontal surface the normal force equals the weight: N = mg. On an inclined plane at angle θ from horizontal, the component of gravity perpendicular to the surface is N = mg·cos θ, and the component pulling the object down the slope is mg·sin θ. The net force along the slope is therefore mg·sin θ − μ·mg·cos θ; if this is positive the object accelerates downward, and if negative static friction holds it in place (this calculator uses kinetic μ throughout).
Limitations: the Coulomb model holds well for dry sliding contact at moderate speeds and pressures. It breaks down for lubricated surfaces, rolling contact, very high pressures, and speeds approaching material limits. Static friction (starting from rest) is typically 10–20% higher than kinetic friction and is not separately modelled here.
Frequently asked questions
Static friction acts when the object is not moving; it can be anywhere from zero up to μ_s·N and always exactly cancels the applied force until motion begins. Kinetic friction acts during sliding and equals μ_k·N (constant). This calculator uses kinetic friction. Typical μ_s is 10–20% higher than μ_k.
In the Coulomb model, increasing the area distributes the same normal force over more surface, reducing the pressure per unit area proportionally — so the total friction force stays constant. This counter-intuitive result holds well for dry, macroscopically smooth surfaces.
An object begins to slide when tan θ > μ, i.e. when the incline angle exceeds arctan(μ). For μ = 0.5 that is about 26.6°. You can read this directly from the net-force sign in the results.
Also known as
TG we-Calculate Editorial Team. (2026). Friction Force Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/friction-calculator
TG we-Calculate Editorial Team. "Friction Force Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/friction-calculator.
TG we-Calculate Editorial Team, "Friction Force Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/friction-calculator
@misc{wecalculate_friction_calculator, title = {Friction Force Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/friction-calculator}}, year = {2026}, note = {TG we-Calculate} }
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