Nov 30, 2019

What's in a Name, Mach

Ernst Waldfried Josef Wenzel Mach (d.1916) was an Austrian physicist and philosopher, noted for his contributions to physics such as study of shock waves. The ratio of one's speed to that of sound is named the Mach number in his honor.

Mach's main contribution to physics involved his description and photographs of spark shock-waves and then ballistic shock-waves. He showed when a bullet or shell moved faster than the speed of sound; it created a compression of air in front of it. Using schlieren photography, he and his son Ludwig were able to photograph the shadows of the invisible shock waves.

In homage, his name was given to: Mach, a lunar crater; Mach bands, an optical illusion; Mach number, the unit for speed relative to the speed of sound.

During the 1860s he discovered the physiological phenomenon that has come to be called Mach’s bands, the tendency of the human eye to see bright or dark bands near the boundaries between areas of sharply differing illumination.

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