Lane Ayres, age 119 of Frankfort, In ,, for the question:

What does the term Mach 1 mean?

The sound barrier is a big problem for speeding airplanes. As the plane reaches the speed of sound, a dense wall of air builds up ahead of it   a wall which must be crashed and scattered. The sound barrier got its name because the air cannot get out of the way of a plane traveling at the speed of sound. In designing and flying planes, this significant speed has been given a name. It is called Mach 1.

Mach numbers are given to fast airplane speeds rather than miles per hour. They indicate the ratio of the speed of sound to the speed of the plane. Mach 2 is twice, and Mach 3 is three times the speed of sound. Through ordinary air, the speed of sound is about one mile in five seconds, but it varies with temperature.