| Mach number The ratio of the speed of a body to the speed of sound in a particular medium, usually the Earth's atmosphere. For example, an aircraft flying through air at twice the speed of sound has a Mach number of 2. The Mach number of an aircraft travelling at a given velocity depends on the altitude of the aircraft and other atmospheric conditions that affect the speed of sound near the aircraft. See also subsonic, supersonic, transonic. |
The speed of an object, measured in multiples of the speed of sound. Thus, an airplane traveling at the speed of sound is said to be at Mach 1; at twice the speed of sound, it is said to be at Mach 2.
Note: The unit is named after Ernst Mach, an Austrian physicist of the nineteenth century.
in fluid mechanics, ratio of the velocity of a fluid to the velocity of sound in that fluid, named after Ernst Mach (1838-1916), an Austrian physicist and philosopher. In the case of an object moving through a fluid, such as an aircraft in flight, the Mach number is equal to the velocity of the object relative to the fluid divided by the velocity of sound in that fluid. Mach numbers less than one indicate subsonic flow; those greater than one, supersonic flow. Fluid flow, in addition, is classified as compressible or incompressible on the basis of the Mach number. For example, gas flowing with a Mach number of less than three-tenths may be considered incompressible, or of constant density, an approximation that greatly simplifies the analysis of its behaviour. For Mach numbers greater than one, shock wave patterns develop on the moving body because of compression of the surrounding fluid. Streamlining alleviates shock wave effects