Static vs Kinetic Friction
See the difference between fₛ (adjustable up to μₛN) and fₖ (constant) in action.
Key Notes
Static friction f_s adjusts to match applied force, up to a maximum: f_s ≤ μ_s N.
Once motion begins, kinetic friction takes over: f_k = μ_k N (constant).
Generally μ_k < μ_s — which is why it's harder to start moving than to keep moving.
Friction acts parallel to the surface, opposing (actual or impending) relative motion.
Formulas
Max static friction
Upper bound on static friction.
Kinetic friction
Constant once moving.
Important Points
Friction is independent of area of contact (classical approximation) but depends on N.
Static vs Kinetic Friction notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.