Jack Fowble, age 14, of Seattle, 'WA for his question:

Where does the word Mach come from?

Ernst Mach was an Austrian scientist. He was curious about speed and about what happened to bodies moving at high speed through various gases. He worked out a method for measuring their speed in terms of the speed of sound. Mach died in 1916 and his work did not seem important until we wanted planes to fly faster than the speed of sound.

Then we needed a measuring unit to compare plane speed with the speed of sound. We named it in honor of Ernst Mach. Mach I is the speed of sound. Mach II is twice the speed of sound. Mach V is five times the speed of sound which, in ordinary air, is about one mile per second.