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 rear axle was optional, and the 428 CJ/SCJ included a "traction lok" with a 3.91 or 4.30 ratio, 31 spline axle shafts and a nodular case. In 1970, the 3.91 ratio was a "traction-lok", while the 4.30 ratio was a Detroit Locker. Mach 1s came with upgraded suspension to varying degrees dependent upon powertrain choices. Big block cars had front shock tower reinforcement, thicker sway bars (no rear bar for 69), and heavier springs and shocks. 428 CJ/SCJ 4 speed cars also came with staggered rear shocks. Standard on Mach 1s was a fierce but cosmetic hood scoop that had