Inclined Plane (with Friction)

On a frictionless incline at angle θ: a = g sinθ (down the slope), N = mg cosθ.

With kinetic friction μ: a = g(sinθ − μ cosθ).

Block stays at rest if tanθ ≤ μ_s. Angle of repose: θ_r = tan⁻¹(μ_s).

Going up: a = −g(sinθ + μ cosθ) (friction adds to gravity along slope).