Mach number a small area around the object's leading edge. (Fig.1b) Fig. 1. "Mach number in transonic airflow around an airfoil; M < 1 (a) and M > 1 (b)." When an aircraft exceeds Mach 1 (i.e. the sound barrier), a large pressure difference is created just in front of the aircraft. This abrupt pressure difference, called a shock wave, spreads backward and outward from the aircraft in a cone shape (a so-called Mach cone). It is this shock wave that causes the sonic boom heard as a fast moving aircraft travels overhead. A person inside the aircraft will not hear this.
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