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 than six factory performance Mustang models were available (GT, Boss 302, Boss 429, Shelby GT350, Shelby GT500 and the Mach 1). Additionally, seven variations of V-8s were available in the '69–'70 models; most of these also available in the new Mach 1. Due to the Mach 1's success, the GT model was discontinued after 1969 following poor sales of 5,396 units versus the 72,458 sales for the Mach 1. The Mustang would not wear the "GT" badge again until 1982. The Mach 1 package was only available in the 'SportsRoof' body style (previously known as the 'Fastback'); never on the