Friction Calculator
Friction on the flat or a slope, with the angle of repose.
Work out Friction. Friction on the flat or a slope, with the angle of repose. Free, with no account and nothing to download.
Rubber on dry road 0.7, steel on steel 0.6, ice on ice 0.05, PTFE 0.04.
Anything pushing it along the surface, on top of gravity.
Friction force
29.42 N
It holds — friction exceeds the driving force
Friction does not depend on contact area, which is the part nobody believes on first hearing. A brick slides the same whichever face is down, because spreading the same weight over more area reduces the pressure in exact proportion. On a slope the normal force is mg·cos θ rather than mg, so friction falls as the slope steepens at the same time as gravity's pull along the slope rises. Both work against you at once, which is why the transition from gripping to sliding feels so sudden. The angle of repose, arctan(μ), is the slope at which something begins to slide under its own weight, and it depends on nothing but the coefficient — not mass, not size. It is why every loose pile of the same material settles to the same angle.
How the Friction Calculator works
Enter mass, coefficient and slope angle for the friction force, the normal force and whether the object actually moves. It also gives the angle of repose — the slope at which something begins to slide under its own weight.
Also known as: coefficient of friction calculator · angle of repose calculator · inclined plane friction calculator · friction force formula
Frequently asked questions
How do I calculate friction force?
f = μN, where N is the normal force. On the flat that is mg; on a slope it is mg·cos θ, which is smaller.
Does contact area affect friction?
No, and almost nobody believes this at first. A brick slides the same whichever face is down, because spreading the same weight over more area reduces the pressure in exact proportion.
What is the angle of repose?
arctan(μ) — the slope at which an object starts to slide under gravity alone. It depends on the coefficient and nothing else, which is why every loose pile of the same material settles to the same angle.
Why does sliding feel so sudden on a slope?
Because both effects work against you at once. As the slope steepens, gravity's pull along it rises while the normal force and therefore friction fall. The margin closes from both ends.
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