Science Sunday: Breaking the Sound Barrier

In October of 2012, Felix Baumgartner broke the world record for the highest and fastest skydive. He fell 128,100 feet from a hot air balloon, and his maximum speed was 833.9 miles per hour. He was the first human to break the sound barrier unaided by a vehicle. Impressive! You can watch a video of the entire fall here. Kurt told me about this guy while we were waiting for the bus to take us home from church this morning. He was going through Facebook on his phone and saw a post about scientists who are designing an Iron Man-like suit, which would allow a wearer to fall from space without a parachute. I wanted to know if it would hurt when you went through the atmosphere, and he said, “No, humans have fallen from space before, and with the right protective suit, you’d be fine.”

“Wouldn’t you break the sound barrier?”

“Well, yes.”

“But what does that mean?”

And so this post was conceived. When we got home, Kurt got out the white board and began explaining.

“So normally, when you have a source of sound, you have waves going out from it, like a ripple.” Image

But when your source of sound is moving, *draws ovals around a second dot, just below the first circles* the ripples won’t be perfectly circular; they will be oblong, like this.”

“Those aren’t the best circles. Or ovals.”

“I know; they’re terrible.”

“Do you want to redo them?”

“No.”

“So this one *draws larger set of circles around a magnet* is moving at the speed of sound. As a result, it’s keeping up with the front edge of those sound waves it produces.

Image

*draws blue line* So when the edges of the sound waves stack up–because sound waves are just pressure waves–it’s the sum of the pressure of all the sound waves that have stacked up. This forms the sound barrier. *places 2nd magnet* so when you break the sound barrier, you get this sort of… shock wave. This is a sonic boom. And the way to draw the sound propagating from that is to just draw circles, because the sound is falling behind the source.” *draws circles*

Image

And that, friends, is why you cannot have a conversation with someone when you are running or biking together and one of you is more than a few feet ahead of the other. If you yell loud enough, your friend in front of you will still hear you, because there is still sound traveling in front of you, as you haven’t hit the sound barrier yet. The speed of sound is 340.29 meters per SECOND. That’s about a mile every 5 seconds. If you could bike that fast, I doubt anyone would want to be your biking partner anyway.

Welp! I learned something today. Did you?

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