Sound speed is considered in Mach numbers as a standard because Mach number is a dimensionless quantity that allows us to compare the speed of an object to the speed of sound in the surrounding medium.
The speed of sound is the speed at which sound waves propagate through a medium, such as air. It varies depending on factors such as temperature, altitude, and composition of the medium. In dry air at sea level and at a temperature of approximately 20 degrees Celsius (68 degrees Fahrenheit), the speed of sound is around 343 meters per second (about 1,125 feet per second).
Using the speed of sound as a reference point allows us to express the speed of an object in terms of multiples of the speed of sound. This is where the concept of Mach number comes in. The Mach number is defined as the ratio of the speed of an object to the speed of sound in the same medium.
For example, if an airplane is flying at a speed equal to the speed of sound, its Mach number would be 1. If it is flying at twice the speed of sound, its Mach number would be 2, and so on. Mach numbers enable us to describe the velocity of an object relative to the speed at which disturbances, such as pressure waves or shock waves, propagate through the medium.
Using Mach numbers as a standard allows for a convenient and consistent way to compare and discuss the speed of objects in relation to the speed of sound, regardless of the specific conditions of the medium in which they are traveling.