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
Ford Mustang Mach 1 (without Ram Air) remained optional on every model. Chart does not reflect the Boss 351 variant of the 351 Cleveland or 250cid I6, as neither were available in the Mach 1 package. The 1972 R-code 351HO package - essentially the solid-lifter Boss 351 motor from 1971 with a reduction in compression from 11.0:1 to 8.8:1 - is listed here, as it was available with the Mach 1 package that year. The Mach 1 name continued with the advent of the Mustang II in 1974. The downsized vehicle - fitted with the 2.8 L V6 rated at - outsold the Mach