Things Faster Than the Speed of Sound

The speed of sound in dry air at 20°C is 343 metres per second — roughly 1,235 km/h or 767 mph. We call this Mach 1. Anything moving faster than Mach 1 through air is "supersonic."

Breaking the sound barrier was once thought impossible. Then Chuck Yeager did it in 1947, and now it's something jet fighters do casually. But the list of things that travel faster than sound — naturally, occasionally, or by design — is surprisingly varied.

What "the sound barrier" actually is

As an object approaches the speed of sound, the air it's pushing aside doesn't have time to flow around it smoothly. Pressure waves pile up at the leading edge, creating a steep wall of compressed air — a shockwave. The "barrier" is this resistance: just below Mach 1, drag rises sharply, and aircraft of the 1940s struggled to push through it.

Once you're past Mach 1, the shockwave actually trails behind you, and aerodynamic forces stabilise (in different ways than at subsonic speeds, but more predictably). The shockwave is what creates the sonic boom — a single continuous wave of pressure that you hear as a sharp crack when it passes you.

The speed of sound isn't constant

"The speed of sound" needs a qualifier. In dry air at 20°C, it's 343 m/s. But:

• In warmer air, sound moves faster. At 30°C, it's about 349 m/s.
• In colder air at high altitude (around 11,000 m), it drops to about 295 m/s.
• In water, sound moves at about 1,500 m/s — over four times faster than in air.
• In steel, sound moves at about 5,100 m/s.
• In diamond (the fastest of any common material), it's about 12,000 m/s.

So "supersonic" is context-dependent. A submarine moving at 30 m/s underwater isn't supersonic — it's subsonic for water. A bullet moving at 500 m/s through air is supersonic for air but slower than sound in water. See the speed of sound on our scale.

Things faster than sound: a tour

Sticking with the air baseline (343 m/s), here's a guided tour of supersonic items, from "casually exceeds" to "absurdly above":

Mach 1-2: Casually supersonic

Whip crack (Mach 1+). The cracking sound of a stockwhip is a small sonic boom. The whip's tip moves at over 343 m/s when properly snapped. This was actually the first human-made supersonic phenomenon — predating gunpowder. See on our scale.

Bullets (Mach 2-3). Most rifle rounds are well into supersonic territory. A .50 BMG round travels at around 900 m/s — Mach 2.6. The crack you hear from a passing rifle bullet is its sonic boom. See on our scale.

Concorde (Mach 2). The retired supersonic passenger jet cruised at 603 m/s, just over Mach 2. It crossed the Atlantic in 3.5 hours, fast enough to follow the sunset westward and arrive "before" you left, by local time. No successor exists, in 2026 still no commercial supersonic flight. See on our scale.

Mach 3-6: Genuinely fast

SR-71 Blackbird (Mach 3.3+). The fastest air-breathing aircraft ever flown, retired in 1998. The SR-71 routinely cruised above Mach 3, with measured speeds exceeding 980 m/s. It outran missiles. See on our scale.

Tank shells (Mach 5). Modern armour-piercing fin-stabilised discarding-sabot rounds (APFSDS) leave the muzzle at around 1,700 m/s. They're depleted uranium darts that penetrate armour through pure kinetic energy — no explosive. See on our scale.

X-15 (Mach 6+). A rocket-powered research aircraft from the 1960s. Reached over 2,000 m/s in level flight — fast enough to qualify pilots as astronauts (above 50 miles altitude). Carried by a B-52 to altitude, then dropped and rocket-powered. See on our scale.

Mach 10+: Hypersonic

Above Mach 5 is officially "hypersonic." The air behaves differently at these speeds — flow becomes turbulent in new ways, leading edges glow from compression heating, and conventional aerodynamics start to break down.

Pyroclastic flows (Mach 0.7). Wait — this one's below Mach 1, but it's worth noting it almost gets there. The 1902 Mount Pelée pyroclastic flow reached about 250 m/s. That's not hypersonic, but it makes you realise how genuinely fast volcanic eruptions can be. See on our scale.

Thrust SSC land-speed record (Mach 1.02). The first land vehicle to break the sound barrier, in 1997. Andy Green drove this jet-powered car at 1,228 km/h across the Nevada desert. The shockwave rolled spectators 2 km away. See on our scale.

Apollo Saturn V at escape velocity (Mach 33). The Saturn V moon rocket reached 11,200 m/s — escape velocity — about 12 minutes after launch. See on our scale.

International Space Station orbital velocity (Mach 22). The ISS orbits Earth at about 7,660 m/s. That's why a sunrise happens every 90 minutes for astronauts onboard. See on our scale.

Beyond rocket speeds

From here, things get astronomical:

Parker Solar Probe (Mach 540). The fastest human-made object ever, at perihelion. Reaches around 191,000 m/s as it whips around the Sun. Its heat shield endures temperatures of 1,400°C while the instruments inside stay at room temperature. See on our scale.

Earth's orbital velocity (Mach 87). Already covered in our other article — 29,800 m/s around the Sun. You're doing this right now.

Solar wind (Mach 1,000+). The stream of charged particles flowing from the Sun reaches 400-800 km/s in the inner Solar System. See on our scale.

Cosmic ray particles (~Mach 870,000). Individual subatomic particles arriving from deep space have been measured at 99.999...% of the speed of light — about 299,790,000 m/s. The energy in a single proton can rival a thrown baseball. See on our scale.

Why "Mach numbers" matter

For ordinary speed, "metres per second" works fine. For high-speed aerodynamics, it's the ratio to the speed of sound that matters. Two reasons:

First, aerodynamic drag and lift behave very differently above and below Mach 1. An aircraft designed for subsonic flight doesn't suddenly become a supersonic aircraft if you push it harder — it gets dragged down by the shockwaves it creates. Different aircraft designs are needed for subsonic, transonic, and supersonic regimes.

Second, the speed of sound varies with altitude (because temperature varies with altitude). An aircraft cruising at Mach 2 at high altitude is moving slower (in metres per second) than the same aircraft at low altitude, because the sound speed at altitude is lower. The Mach number captures something physically meaningful that absolute speed doesn't.

The honest perspective

The speed of sound in air sits in a particularly interesting position on the scale of speeds. It's fast enough to be impressive — faster than most things people encounter — but it's almost nothing compared to space-relevant speeds. The "sound barrier" felt insurmountable in the 1940s, but turned out to be a trivial obstacle compared to the energy thresholds of orbital flight, let alone interstellar travel.

Sound speed is the speed of information through molecules in air. It's slow because molecules are heavy and air is dilute. In a perfect vacuum, sound doesn't travel at all — there's nothing for the pressure waves to travel through.

The fastest man-made object ever (Parker Solar Probe) is moving about 555 times faster than sound. The fastest natural object we know of (cosmic ray particles) is moving roughly 870,000 times faster than sound. There's a lot of velocity range available above the sound barrier — we've barely begun to explore it.