What is Mach Number ? History and The importance of Mach

What is Mach?

 

Mach, sometimes also referred to as a Mach number,  is a speed measurement based on the speed of sound. Since sound travels at different speeds in different conditions, the calculations here are given for 20°C in dry air at sea level. 

Symbol
Mach, Ma, M

Mach can be abbreviated as M, and is also sometimes abbreviated as Ma. For example, Mach 1 can be written as 1 M or 1 Ma.

Although Mach can be abbreviated M or Ma, the Mach number is typically expressed with the number after the unit name. For example, the expression Mach 3 is preferred rather than 3 Machs or 3 M.

The speed is classified as either subsonic, transonic, supersonic, or hypersonic depending on the Mach number.

Other name
Mach number

History

The Mach number is named after Moravian physicist and philosopher Ernst Mach, and is a designation proposed by aeronautical engineer Jakob Ackeret in 1929.

The importance of Mach

Mach is typically used in aviation and space exploration.
Mach 1 is traveling at the speed of sound; Mach 2, twice the speed of sound, and so on. In dry air at 0°C, the speed of sound is 1,193.3 kilometers per hour (741.5 miles per hour).

Only military aircraft are permitted to reach Mach 1 over the United States. The British-French Concorde airliner did reach supersonic speeds on its transoceanic flights, and had a Mach meter on the forward bulkhead of its passenger cabin.

Flight can be roughly classified in six categories:

Regime	Subsonic	Transonic	Speed of sound	Supersonic	Hypersonic	Hypervelocity
Mach	<0.8	0.8 – 1.2	1.0	1.2–5.0	5.0–10.0	>8.8