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Q&A: Speed of Sound vs. Speed of Light

18 Apr 2016, 07:01 UTC
Q&A: Speed of Sound vs. Speed of Light
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Question: I was outside yesterday and heard a loud sound up in the sky, kind of like a long roar. When I looked up I saw this airplane going over, but the sound was coming from way behind it in empty sky. The sky was clear, so nothing was hiding behind clouds, and that was the only airplane I could see. When I asked my teacher about it, he said something about the speed of light being faster than the speed of sound. But that didn’t really help me understand why the sound was behind the airplane. A friend told me to ask the question here, so maybe you can help? I’m in 6th grade, so please don’t get too complicated. Thanks! —VC, Billings, MT
Answer: I remember the first time I noticed that effect, and when I asked my uncle (a scientist) he said the same thing: the speed of light is faster than the speed of sound. By itself, that’s a correct answer to the question. But without further explanation, most people won’t really grasp what those two speeds have to do with the illusion. Here’s the numbers:

speed of sound = 340 m/s = 768 mph
speed ...

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