Mach (20°C, 1 atm) to Cosmic Velocity - First

Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium. Mach 1 at 20°C, 1 atm equals approximately 343.6 m/s (1,235 km/h).

Mach = velocity ÷ speed_of_sound. At 20°C: Mach 1 = 343.6 m/s. Speed of sound = √(γRT/M) where γ = heat capacity ratio.

To m/s (at 20°C): × 343.6. To km/h (at 20°C): × 1,237. Note: changes with altitude and temperature.

Fighter jets (Mach 1.5–2.5), commercial aircraft (Mach 0.8–0.85), space shuttle reentry (Mach 25), and missile speeds.

Concorde: Mach 2.04. SR-71 Blackbird: Mach 3.3. X-15: Mach 6.7. Meteorites enter at Mach 50+. Subsonic <1, supersonic >1, hypersonic >5.

Thinking Mach is constant — it varies with temperature/altitude. At 30,000 ft, Mach 1 ≈ 295 m/s (colder air = slower sound).

Mach 1 = speed of sound. Below Mach 1 = subsonic. Mach 1–5 = supersonic. Above Mach 5 = hypersonic. It's a ratio, not a fixed speed.

The first cosmic velocity (escape velocity from Earth's surface to orbit) is approximately 7,900 m/s (7.9 km/s), the minimum speed needed to achieve Earth orbit.

v₁ = √(GM/r) where G is gravitational constant, M is Earth's mass, r is Earth's radius. Approximately 7.9 km/s.

To km/h: × 3,600. To mph: × 17,672. 7.9 km/s = 28,440 km/h = 17,672 mph.

Minimum speed for satellites, space station orbit, and low Earth orbit (LEO) calculations.

ISS orbits at ~7.66 km/s. Below this speed, you fall back to Earth. Above it, you stay in orbit (if horizontal).

Confusing with escape velocity (second cosmic velocity, 11.2 km/s) — orbital velocity is lower.

Remember: ~8 km/s for orbit, ~11 km/s to escape. v₁ is minimum for orbit, not escape.