Mach number which was also unit-first, and may have influenced the use of the term Mach. In the decade preceding faster-than-sound human flight, aeronautical engineers referred to the speed of sound as "Mach's number", never "Mach 1". Mach number is useful because the fluid behaves in a similar manner at a given Mach number, regardless of other variables. As modeled in the International Standard Atmosphere, dry air at mean sea level, standard temperature of , the speed of sound is . The speed of sound is not a constant; in a gas, it increases as the absolute temperature increases, and since atmospheric
Mach (crater) Mach (crater) Mach is a large lunar impact crater of the class known as a walled plain. It is located on the far side of the Moon and cannot be viewed directly from the Earth. Nearby craters of note include Joule to the northeast, Mitra attached to the western outer rim, and Henyey to the southwest. This is a prominent but eroded formation with multiple craters along the rim and interior. The crater Harvey breaks across the eastern rim, and its outer rampart spills across the interior floor of Mach. The overall shape of Mach resembles a pear, with a