Mach Numbers and the Sound Barrier
理解する Supersonic Speed
Learn About MachWhen an aircraft reaches Mach 1, it's traveling at the speed of sound. Go faster, and you're supersonic. But what exactly is a Mach number, why does the speed of sound change, and what happens when you break the sound barrier? This guide explains the physics behind some of the fastest speeds humans achieve.
What Is a Mach Number?
Mach number is the ratio of an object's speed to the local speed of sound:
Mach = Object speed ÷ Speed of sound
- Mach 0.5: Half the speed of sound (subsonic)
- Mach 1.0: The speed of sound (sonic)
- Mach 2.0: Twice the speed of sound (supersonic)
Named after Austrian physicist Ernst Mach (1838-1916), who studied shock waves.
Why the Speed of Sound Varies
The speed of sound depends on air temperature (and thus altitude):
| Altitude | Temperature | Speed of Sound |
|---|---|---|
| Sea level | 15°C (59°F) | 761 mph (1,225 km/h) |
| 10,000 ft | -5°C (23°F) | 722 mph (1,162 km/h) |
| 20,000 ft | -25°C (-13°F) | 685 mph (1,102 km/h) |
| 35,000 ft | -54°C (-65°F) | 660 mph (1,062 km/h) |
| 40,000 ft | -57°C (-70°F) | 659 mph (1,061 km/h) |
Sound travels faster in warmer air because air molecules move more energetically.
Speed Regimes
| Regime | Mach Range | Characteristics |
|---|---|---|
| Subsonic | Below Mach 0.8 | Normal airflow, most aircraft |
| Transonic | Mach 0.8-1.2 | Mixed sub/supersonic flow, instability |
| Supersonic | Mach 1.2-5.0 | Shock waves, sonic booms |
| Hypersonic | Mach 5.0-10.0 | Extreme heating, specialized vehicles |
| High hypersonic | Above Mach 10 | Re-entry vehicles, theoretical aircraft |
Mach Conversion at Different Altitudes
At Sea Level (15°C)
| Mach | MPH | KM/H |
|---|---|---|
| 0.5 | 380 | 612 |
| 0.85 | 647 | 1,041 |
| 1.0 | 761 | 1,225 |
| 2.0 | 1,522 | 2,450 |
| 3.0 | 2,283 | 3,675 |
At Cruise Altitude (35,000 ft, -54°C)
| Mach | MPH | KM/H |
|---|---|---|
| 0.5 | 330 | 531 |
| 0.85 | 561 | 903 |
| 1.0 | 660 | 1,062 |
| 2.0 | 1,320 | 2,124 |
| 3.0 | 1,980 | 3,186 |
“The first supersonic flight was made by Chuck Yeager in the Bell X-1 on October 14, 1947, reaching Mach 1.06 at 43,000 feet.”
Famous Aircraft Speeds
| Aircraft | Max Mach | MPH | KM/H |
|---|---|---|---|
| Boeing 747 | 0.92 | ~614 | ~988 |
| Concorde | 2.04 | ~1,350 | ~2,173 |
| F-22 Raptor | 2.25 | ~1,500 | ~2,414 |
| SR-71 Blackbird | 3.32 | ~2,193 | ~3,529 |
| X-15 (record) | 6.70 | ~4,520 | ~7,274 |
| Space Shuttle (re-entry) | ~25 | ~17,500 | ~28,000 |
Why Mach Numbers Matter
Aircraft Design
Aerodynamics change dramatically at different Mach regimes. Aircraft designed for subsonic flight won't work supersonically, and vice versa.
Pilot Communication
Pilots use Mach numbers at high altitudes because true airspeed becomes misleading as air density changes. "Mach 0.85" means the same thing regardless of altitude.
Structural Limits
Aircraft have maximum operating Mach numbers (Mmo) beyond which structural damage or control problems occur.
まとめ
Mach numbers provide a universal way to describe speed relative to sound—essential in aviation and aerospace. Mach 1 is the speed of sound, which varies with temperature (about 660-760 mph depending on altitude). 理解する Mach numbers helps interpret aircraft performance data and appreciate the remarkable achievement of supersonic and hypersonic flight.