Dry Friction

Dry (Coulomb) friction opposes motion between solid surfaces in contact. Force magnitude depends on the normal force and a coefficient of friction.

Formulas

• Static: F_s ≤ μ_s N
• Kinetic: F_k = μ_k N

Example

With μ_k=0.25 and N=120 N: F_k = 0.25 × 120 = 30 N.

FAQs

Static vs kinetic?
Static holds objects at rest; kinetic applies during sliding.

Surface effects?
μ depends on materials, roughness, and lubrication.