Friction Force Calculator

Formula

How this is calculated

Friction force is the product of the coefficient of friction and the normal force pressing the two surfaces together: f = μ·N. Enter the coefficient μ (dimensionless) and the normal force N in newtons to get the friction force f directly. The static/kinetic selector is a label: use the static coefficient μ_s for the maximum force before motion begins, or the kinetic coefficient μ_k for the force once sliding.

If you leave the normal force blank, it is derived from mass and surface angle as N = m·g·cos θ, where g = 9.80665 m/s² and θ is the incline angle measured from the horizontal (default 0° for a flat surface). On a level surface cos 0° = 1, so N equals the weight m·g; as the incline steepens the normal force decreases. You can also rearrange the relation to find the coefficient as μ = f/N.

Assumptions: dry (Coulomb) friction with a constant coefficient, surfaces in contact, and a normal force that is non-negative. The model ignores air resistance, rolling resistance, and any applied forces along the slope. Static friction reported here is the maximum value μ_s·N; the actual static friction can be anything from zero up to this limit depending on the applied force.