Mach number is the ratio of flight speed to sound speed at that time. It is faster than the speed of sound when it is greater than 1 and slower than the speed of sound when it is less than 1. Mach number was named in memory of Austrian scholar ernst mach (ernst mach, 1838- 19 16).
Mach is generally used in aerospace vehicles such as airplanes and rockets. Because the speed of sound propagation in air varies with different conditions, Mach is only a relative unit, and the specific speed of each Mach is not fixed.
At low temperature, the sound propagation speed is lower, and the specific speed corresponding to 1 Mach is lower. Therefore, relatively speaking, it is easier to reach a higher Mach number at high altitude than at low altitude (the speed of sound at sea level at zero degrees Celsius is about1193km/hr; The speed of sound at an altitude of 10,000 meters is about 1062 km/hr).
I'm glad to answer your question.