Mach, << mahk, >> Ernst (1838-1916), was an Austrian physicist and psychologist. He studied the action of bodies moving at high speeds through gases, and developed an accurate method for measuring their speeds in terms of the speed of sound. This method is important in problems of supersonic flight.
Mach’s work remained obscure until the speed of aircraft began to approach the speed of sound. Then the term Mach number came to be used as a measure of speed. Mach 0.5 is half the speed of sound, or subsonic. Mach 1 is the speed of sound, or transonic. Mach 2 is twice the speed of sound, or supersonic, and so on. See Aerodynamics (Supersonic aerodynamics) .
Mach was deeply interested in the historical development of the ideas on which the science of mechanics is based. He claimed that all knowledge of the physical world comes to us by the five senses–sight, hearing, smell, taste, and feeling. He also taught that a scientific law was only a correlation between observed data. Mach was born at Turas, Moravia.
