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Oh, hi kids. I'm Dr. Darden, an engineer here at NASA Langley Research Center. I've done

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sonic boom research here for many many years. What's a sonic boom? Doesn't it have to do

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with the speed of airplanes? Yes it does. A sonic boom occurs when an airplane travels

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faster than the speed of sound. We do lots of sonic boom testing in this wind tunnel.

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In fact, the first models that we used were no larger than my fingernail. When an airplane

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travels through the air, it generates pressure waves that travel at the speed of sound in

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all directions. A plane flying at the speed of sound moves at the same speed as the disturbances,

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causing a shock wave to form. When the plane flies faster than the speed of sound, this

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shock wave forms a cone shape attached to the nose of the airplane. Air pressure just

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inside the cone is high, and air pressure ahead of the cone is normal. This shock wave

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or cone extends to the ground, perhaps 10 to 15 miles. The sonic boom is heard when

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the sudden change in pressure crosses your ear. Let me demonstrate for you with this

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balloon. The air pressure inside this balloon is higher than the air pressure outside the

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balloon. If I pop the balloon, a shock wave is generated much like a sonic boom. Could

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there be a very high frequency sound that people can't hear but dogs can? Absolutely,

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but remember that very high frequency sound can't come from far away. Because high frequency

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sounds don't travel very far. That's right. Thanks, Dr. Darden. You're welcome. Goodbye

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and good luck.