a ratio of the speed (of an object, etc.) to the speed of sound in the fluid or other medium through which the object travels. Usually used to describe supersonic speeds
The jet traveled at Mach 3.
{i} family name; Ernst Mach (1838-1916), Austrian physicist and philosopher who presented the Mach number for the first time
Mach is used as a unit of measurement in stating the speed of a moving object in relation to the speed of sound. For example, if an aircraft is travelling at Mach 1, it is travelling at exactly the speed of sound. Mach number. a unit for measuring speed, especially of an aircraft, in relation to the speed of sound. Mach 1 is the speed of sound, Mach 2 is twice the speed of sound etc (Ernst Mach (1838-1916), Austrian scientist)