Chuck Yeager was the first person to break the sound barrier. At the time, there was trouble with the planes trying to get up to high speeds because as they would get closer to the speed of sound they would shake pretty furiously and the pilot would begin to lose control.
Chuck had been trying for weeks to go faster and faster, and finally on October 14, 1947, with two broken ribs he was able to make it. As he hit Mach 1, people on the ground heard what they thought was thunder and then a big BOOM.
If you’d like to read more, check out this article on Wired.
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