Science & Engineering

Mach number.

Find the speed of sound in air at a given temperature, then compare an object's speed with it.

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Mach number formula

Mach number is the ratio of object speed to the local speed of sound: M = v ÷ a. For dry air in this simplified model, a = √(γRT), with absolute temperature T in kelvin. Because temperature changes the speed of sound, the same airspeed can have different Mach numbers at different temperatures.

Reference: NASA Glenn Research Center, Speed of Sound and NASA Mach-number definition.