Editing Speed of sound (section)

==Mach number==
{{Main|Mach number}}
Mach number, a useful quantity in aerodynamics, is the ratio of air [[speed]] to the local speed of sound. At altitude, for reasons explained, Mach number is a function of temperature.
Aircraft [[flight instruments]], however, operate using pressure differential to compute Mach number, not temperature. The assumption is that a particular pressure represents a particular altitude and, therefore, a standard temperature. Aircraft flight instruments need to operate this way because the stagnation pressure sensed by a [[Pitot tube]] is dependent on altitude as well as speed.