why use mach number
The Mach number is a ratio between the aircraft's speed (v) and the speed of sound (a). The Mach number is named for the Austrian physicist, Ernst Mach (1838-1916). Technically, as you can see, the Mach Number is not a speed but a speed ratio. However, it is used to indicate how fast one is going when compared to the speed of sound. Scientifically, the speed at which sound travels through a gas depends on 1) the ratio of the specific heat at constant pressure to the constant volume, 2) the temperature of the gas, and 3) the gas constant (pressure/density X temperature).