Objects that travel faster than the speed of sound (740 mph) are classified as supersonic. Such speed is described by Mach numbers, named after the Austrian physicist Ernst Mach.
A plane moving at the speed of sound is considered to be traveling at Mach 1. When the speed of the plane exceeds Mach 1, an observer may hear a sonic boom, which results from sound waves forming a cone.
The following lesson explains the relationship between the velocity of a moving object and the vertex angle of the sound wave cone it produces.