Mach number

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Mach number is the ratio of an object's speed to the local speed of sound in the surrounding medium. It is dimensionless and is commonly used to classify compressible flows.

Subsonic motion has a Mach number below one, transonic flow lies near one, supersonic flow is above one, and hypersonic flow is commonly taken as greater than five. The local speed of sound depends on temperature, composition, and thermodynamic state.

As Mach number approaches and exceeds one, compressibility, shock waves, heating, and wave drag become important. Different parts of an aircraft or flow can be locally subsonic or supersonic at the same time.

The quantity is used in aerodynamics, rocketry, ballistics, gas dynamics, and atmospheric science. It is named after physicist Ernst Mach.

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• Source / publisher: Wikipedia
• URL type: WWW
• Credits: Wikipedia
• URL: https://en.wikipedia.org/wiki/Mach_number