The sound spreads through the air very quickly. When an airplane reaches a speed equal to that of sound, its speed is said to be equal to Mach 1.
The sound moves through the air at a speed of 340 meters per second. In an hour it travels, then. 1 200 kilometers. Mach 1 is a unit of speed equivalent to that of sound. Consequently, Mach 2 will correspond to a speed of 2 400 kilometers per hour. In the latter case, the rocket or plane reaches a certain point before the noise produced by its engine. Then you hear a "concentration" of noises, called a "double bang". Ernst Mach is the name of an Austrian professor of physics and philosophy, born in 1838 and died in 1916.
 |
| FA 18 Hornet breaking sound barrier |
.
