- a number indicating the ratio of the speed of an object to the speed of sound in the medium through which the object is moving. Abbreviation: M
- short for Mach number
- Ernst (ɛrnst). 1838–1916, Austrian physicist and philosopher. He devised the system of speed measurement using the Mach number. He also founded logical positivism, asserting that the validity of a scientific law is proved only after empirical testing
- (often not capital) the ratio of the speed of a body in a particular medium to the speed of sound in that medium. Mach number 1 corresponds to the speed of soundOften shortened to: Mach
measure of speed relative to the speed of sound (technically Mach number), 1937, named in honor of Austrian physicist Ernst Mach (1838-1916).
- Austrian physicist and philosopher who experimented with supersonic projectiles and the flow of gases, obtaining early photographs of shock waves and gas jets. His work laid an important foundation for later developments in the science of projectiles and aeronautical design, and the Mach number and Mach bands were named for him.
- 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.