Static and kinetic dry friction
Static friction is a responsive force with an approximate limit.
Key knowledge
In the simple dry-contact model, static friction adjusts to prevent tangential relative slip up to |F_s|≤μ_sN. During sliding, kinetic friction has magnitude approximately μ_kN and opposes relative sliding at the contact. Static friction need not be at its limit and can accelerate a body or act in its direction of motion.
Values and equations
|F_s|≤μ_sN; |F_k|≈μ_kN
- F_s,F_k,N
- Static/kinetic tangential contact force and normal-force magnitude N
- μ_s,μ_k
- Static-limit and kinetic dry-friction coefficients 1
Conditions and scope
- N≥0; empirical coefficients belong to the specified material pair and operating conditions.
- These relations are approximations, unsuitable as universal models of lubricated, adhesive, high-speed or velocity-dependent contacts. The direction is set by relative slip or the tendency to slip at the interface.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read §6.2 Static and Kinetic Friction, equations6.1–6.2 and empirical-model limitations. Do not adopt the source’s occasional shorthand “opposes motion” without the relative-contact qualifier, nor a universal μ<1 or μ_s>μ_k claim.
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Entry details
Permanent link to this entry ↗- Record identity
- foundation-physics-dry-friction
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions