| 词汇 | mach number |
| 词源 | Mach number; Mach angle. Mach number is the ratio of the speed of a body to the speed of sound in air. Almost exclusively used to measure flight speed, it has only become common in the last few decades, as increased aircraft speeds have made old mph measurements too cumbersome. Mach 1, for instance, is the speed of sound, 762 miles per hour at sea level, while Mach 2 is twice the speed of sound. The word derives from the name of German scientist Ernst Mach (1838–1916), who died 31 years before Captain Charles Yeager first broke the sound bar- rier over Edwards Air Force Base in Muroc, California. (On October 14, 1947 Chuck Yeager flew his Bell X-I rocket plane at Mach 1.015.) Because of Mach’s investigations into the super- sonic speed of projectiles and the shock waves produced at these speeds both the measurement unit and the Mach angle, the angle a shock wave makes with the direction of flight, were named in his honor. |
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