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Maximum Static Friction (f = μₛN)

Also known as breakaway friction

fs,max⁡=μsNf_{s,\max} = \mu_s N

Worked example: μs 0.6 on 500 N normal → 300 N — press Try an example to run it live, then adjust anything.

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Friction holds on →

Grade 11Grade 11 Physics

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UniversityEngineering Mechanics

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Maximum Static Friction (f = μₛN) explained

Nfsμs

Static friction is the only force in introductory mechanics that is written with an inequality: f ≤ μₛN. It supplies exactly whatever is needed to prevent sliding, up to a ceiling of μₛN, and this formula computes that ceiling. Press a 500 N normal load onto a surface with μₛ = 0.6 and you can push with anything up to 300 N and nothing moves; at 301 N the object breaks free and the weaker kinetic friction takes over.

That inequality is the single biggest trap: plugging μₛN in as "the friction force" on a stationary object is wrong unless the object is on the verge of slipping. The distinction pays real dividends — a car's tyres grip through static friction as long as they roll, which is why ABS pumps the brakes to keep them from locking into a lower-μₖ skid, and why a driven wheel spinning on ice suddenly has far less traction than one that is merely rolling.

Maximum Static Friction (f = μₛN) formula

fs,max⁡=μsNf_{s,\max} = \mu_s N
Where
  • fsf_s= Maximum static friction (N)
  • μs\mu_s= Coefficient of static friction
  • NN= Normal force (N)

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