Every moving object constantly broadcasts pressure waves at the speed of sound. Drag the throttle and watch what happens to YOUR waves: at low speed they run ahead and warn the air you're coming; at M = 1 they pile into a wall on your nose; past it they can't escape a cone — the Mach cone. Then hit 🎯 Quiz and read Mach numbers straight off the geometry, like an engineer.
a = √(γRT) — every pulse expands at a, no matter how fast the source moves.sin μ = a·t / (V·t) = 1/M → μ = arcsin(1/M), defined only for M ≥ 1.M = 1/sin μ. This is Anderson §9.2's Mach wave — the infinitely weak limit of an oblique shock.