What Is Mach (Ma)?
Mach, written as Ma, is a unit that tells you how fast something is moving compared to the speed of sound in the air around it. Mach 1 means the object is moving at the same speed as sound. Mach 2 means it is going twice as fast as sound, and Mach 0.5 means it is moving at half the speed of sound.
The important thing to remember is that the speed of sound is not always the same. It changes with temperature and with the kind of gas the sound travels through. So Mach is a comparison, not one fixed speed.
Definition
Mach number is the ratio between the speed of an object and the local speed of sound.
In simple words:
Mach number = (speed of object) ÷ (speed of sound in that place)
For example, if a jet is flying at the speed of sound, its Mach number is 1. If it is flying at three times the speed of sound, its Mach number is 3.
At about 20 °C near sea level, the speed of sound in air is about 343 meters per second, which is about 1235 kilometers per hour or about 767 miles per hour. At this temperature:
- Mach 1 is about 343 m/s
- Mach 2 is about 686 m/s
- Mach 3 is about 1029 m/s
But if the air is colder or thinner, the speed of sound is different, so the exact speed for Mach 1 also changes.
History / Origin
The word Mach comes from the name of an Austrian scientist called Ernst Mach, who lived in the 1800s and early 1900s. He studied how objects move at very high speeds, including speeds close to and faster than the speed of sound.
In the early days of flight, most airplanes were much slower than sound. As aircraft became faster, scientists needed a simple way to talk about how close they were to the speed of sound. They started using Mach numbers in the first half of the 1900s, especially during and after World War II, when jets and rockets were developed.
The idea of Mach number became very important when people studied shock waves, sonic booms, and the problems that happen when aircraft get near or above the speed of sound. Today, Mach numbers are a basic tool in aerodynamics and space science.
Symbol & Abbreviation
The usual symbol for Mach number is Ma. In many books and flight reports, you may see it written as a capital M.
- Name Mach number
- Symbol Ma or M
- Type of unit it is a ratio, so it has no physical dimension
Examples of how it is written:
- Ma 0.8 or M 0.8 means eight tenths of the speed of sound
- Ma 1.0 or M 1.0 means the speed of sound
- Ma 3.5 or M 3.5 means three and a half times the speed of sound
Current Use Around the World
Mach numbers are used all over the world when talking about very fast speeds in air or gas. They are not used much for cars or trains, because those are far below the speed of sound. Instead, Mach is mainly used for:
- Military jets to describe high speed flight, for example Mach 1.5 or Mach 2
- Supersonic and hypersonic aircraft such as experimental planes and research vehicles
- Spacecraft and missiles moving through the atmosphere
- Rockets when they pass through the thick parts of the air near Earth
- Wind tunnels where models are tested at specific Mach numbers
- Weather and gas flow studies for flows in pipes, nozzles, and around objects
Engineers and pilots use Mach numbers because they tell not just how fast something is, but also what kind of airflow and forces they can expect. For example, air behaves differently in these ranges:
- Subsonic Mach less than 1, slower than sound
- Transonic around Mach 0.8 to 1.2, where some parts of the air flow are faster than sound and some are slower
- Supersonic Mach 1 to about Mach 5
- Hypersonic above Mach 5
Example Conversions
Because Mach is a ratio, you first need the speed of sound for your conditions, then you can convert. To keep it simple, we will use the common value of the speed of sound in air at 20 °C near sea level, which is about:
- 343 meters per second
- 1235 kilometers per hour
- 767 miles per hour
From Mach to other speed units
| Mach | m/s (approx) | km/h (approx) | mph (approx) |
|---|---|---|---|
| Mach 0.5 | 171 m/s | 618 km/h | 384 mph |
| Mach 1 | 343 m/s | 1235 km/h | 767 mph |
| Mach 2 | 686 m/s | 2470 km/h | 1534 mph |
| Mach 3 | 1029 m/s | 3705 km/h | 2301 mph |
From speed to Mach using the same simple value for the speed of sound:
- 800 km/h ÷ 1235 km/h ≈ Mach 0.65
- 1000 km/h ÷ 1235 km/h ≈ Mach 0.81
- 2000 km/h ÷ 1235 km/h ≈ Mach 1.62
- 300 m/s ÷ 343 m/s ≈ Mach 0.87
Remember, these are only approximate values. The real Mach value depends on the actual speed of sound where the object is, which changes with temperature and the gas.
Related Units
Mach is related to other units that measure speed. These are some common ones:
- Meters per second (m/s) the standard scientific unit for speed
- Kilometers per hour (km/h) often used for cars, trains, and planes
- Miles per hour (mph) used in some countries for road speeds and aircraft
- Knots (kt) used in aviation and ships, one knot is one nautical mile per hour
- Speed of light (c) used in space science, sometimes speeds are compared to c in a similar way as to Mach, but for light instead of sound
Mach number is different from these because it has no fixed size. It always depends on the local speed of sound. But you can always convert between Mach and these units if you know the speed of sound.
FAQs
Q: What does Mach 1 mean?
A: Mach 1 means an object is moving at the same speed as sound in the air or gas around it. At normal temperature near sea level, this is about 343 m/s or 1235 km/h.
Q: Is Mach a fixed speed?
A: No. Mach is a ratio. Mach 1 is the speed of sound at that place, which changes with temperature and the gas. So Mach 1 on a cold day is slower than Mach 1 on a warm day.
Q: What is the speed of sound?
A: The speed of sound is how fast sound waves travel through a material. In dry air at 20 °C near sea level, it is about 343 m/s. It is faster in warmer air and slower in colder air.
Q: What is supersonic speed?
A: Supersonic speed means faster than the speed of sound, so a Mach number higher than 1. For example, Mach 1.2 or Mach 2 are supersonic speeds.
Q: What is hypersonic speed?
A: Hypersonic speed usually means Mach 5 or higher. At these speeds, the air around an object becomes extremely hot, and special materials and designs are needed.
Q: Why do pilots use Mach instead of km/h or mph?
A: Pilots and engineers use Mach because it tells them how close they are to the speed of sound, which is important for how the aircraft behaves. The same Mach number causes similar airflow effects, even if the exact km/h or mph value changes with altitude and temperature.
Q: Can cars reach Mach 1?
A: Normal cars cannot. A few special rocket powered cars for land speed records have come close to or passed Mach 1, but they are not used on regular roads.
Q: Is Mach used only in air?
A: Mach can be used for any gas or fluid where sound can travel, such as air or other gases. The idea is the same, speed divided by speed of sound in that medium.