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 Five "Mach 6", two different single-seater cars created specifically for stunt races. The designs of the Mach 4 and Mach 6 are vaguely reminiscent of the Mach Five's (as in the original American comics), although the only functions the Mach 6 features are the jump jacks, which are standard equipment in race cars in the movie. Little about the Mach 4 is known, as it appears only briefly in the film and is portrayed as a red-colored companion to the 6. The film portrays the Mach Five as initially being a regular everyday vehicle, justifying the existence of its trunk door