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 (rather than having it serve solely as an excuse for Spritle and Chim-Chim to stow away in the vehicle). The Mach Five is later modified with gadgets and becomes Speed's alternate car for off-track races such as the Casa Cristo 5000, as well as everyday driving like a normal car. The Mach Five originally belonged to Speed's older brother Rex, who relinquished ownership of it to Speed before he left the Racer home. Speed's main car for races on the WRL track (Thunderhead, etc.) is the Mach 6. The Mach 6 was destroyed in a fixed race, but was later