(symbols M, NMa)
(Pronounced mock, after Ernst Mach, 1838-1916, Austrian scientist). A number expressing the ratio of the speed of a body or of a point on a body with respect to the surrounding air or other fluid, or the speed of a flow, to the speed of sound in the medium; the speed represented by this number. See Cauchy number. </dd>
If the Mach number is less than 1, the flow is called subsonic and local disturbances can propagate ahead of the flow. If the Mach number is greater than 1, the flow is called supersonic and disturbances cannot propagate ahead of the flow with the result that shock waves form.
Some authorities use mach number but engineering practice is to use a capital M in all words and combinations employing Mach. [[/a>|/a> ]]
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use