Wednesday, November 4, 2009

Mach number

Mach number (Ma or M) (generally pronounced /ˈmɑːk/, sometimes /ˈmɑːx/ or /ˈmæk/) is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance. It is commonly used to represent an object's (such as an aircraft or missile) speed, when it is travelling at (or at multiples of) the speed of sound.

An F/A-18 Hornet at transonic speed and displaying thePrandtl–Glauert singularity just before reaching the speed of sound
\ M = \frac {{v_s}}{{u}}

where

\ M is the Mach number
\ v_s is the speed of the source (the object relative to the medium) and
\ u is the speed of sound in the medium

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