N-UNCOUNT
马赫(速度单位，1马赫等于1倍音速)
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.
例句
The hot air permitted higher speeds before the critical Mach number was exceeded...
热空气可使之在超过临界马赫数之前达到更快的速度。
The aim is to fly at about Mach 2, twice the speed of sound.
目标是以大约2马赫的速度飞行，也就是音速的两倍。