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Friction Force Calculator

Determine the friction force by the coefficient of friction using the friction force calculator.

Clear
Friction force171.6164 N0.35 × 490.333 N normal force
Normal force490.3325 Nequal to the weight on level ground
Weight490.3325 N
Component down the slope0 Nweight × sin 0°
Net force-171.6164 Nfriction holds it — it stays put
Force still needed to move it171.6164 N
Angle at which it starts to slide19.29°arctan of the coefficient — independent of mass entirely
Coefficient needed to hold this slope0yours is enough
Work done against friction per metre171.6164 Jall of it becomes heat

The formula

F = µN, with N = mg cos θ on a slope

Area does not appear, and neither does mass

Friction is proportional to the force pressing the surfaces together, not to how much of them touch. A wide tyre and a narrow one of the same rubber, under the same load, generate the same friction in the simple model. Real tyres are more complicated, but the first-order result is genuinely area-independent.

The angle at which an object begins to slide is arctan µ, with no mass term at all — because increasing the mass raises the driving component and the friction in exactly the same proportion. A heavy crate and a light one of the same material slide at the same angle, which is a reliably surprising result.

Static friction is usually larger than kinetic, so more force is needed to start something moving than to keep it moving. That is the jerk you feel when a stuck drawer finally gives, and it is why this page takes a single coefficient: use the static value to ask whether it moves, and the kinetic value to ask how fast.