WEBVTT - How Sonic Booms Work

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<v Speaker 1>Welcome to brain Stuff from how stuff works dot com

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<v Speaker 1>where smart Happens. Hi Am Marshall Brain with today's question,

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<v Speaker 1>what causes a sonic boom from an airplane? You can

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<v Speaker 1>learn a lot about sonic booms by looking at the

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<v Speaker 1>wakes that boats leave in the water. If you toss

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<v Speaker 1>a pebble into a pond, little waves will form in

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<v Speaker 1>concentric circles and propagate away from the point of impact.

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<v Speaker 1>If a boat travels through the pond at three to

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<v Speaker 1>five miles per hour, little waves will propagate in the

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<v Speaker 1>same way, both ahead of and behind the boat, and

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<v Speaker 1>the boat will travel through those little waves. If a

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<v Speaker 1>boat travels faster than the waves can propagate through the water,

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<v Speaker 1>then the waves can't get out of the way of

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<v Speaker 1>the boat fast enough and they form awake. Awake is

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<v Speaker 1>a large single wave. It's formed out of all the

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<v Speaker 1>little waves would have propagated ahead of the boat but can't.

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<v Speaker 1>When an airplane travels through the air, it produces sound waves.

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<v Speaker 1>If the plane is traveling slower than the speed of sound,

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<v Speaker 1>which is something like seven miles per hour, then sound

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<v Speaker 1>waves can propagate ahead of the plane. If the plane

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<v Speaker 1>breaks the sound barrier and flies faster than the speed

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<v Speaker 1>of sound. It produces a sonic boom when it flies past.

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<v Speaker 1>The boom is the wake of the plane sound waves.

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<v Speaker 1>All of the sound waves that would have normally propagated

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<v Speaker 1>ahead of the plane are combined together, so at first

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<v Speaker 1>you hear nothing, and then you hear the boom that

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<v Speaker 1>those sound waves create together. It's just like being on

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<v Speaker 1>the shore of a smooth lake when a boat speeds passed.

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<v Speaker 1>There's no disturbance in the water as the boat comes by,

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<v Speaker 1>but eventually a large wave from the wake rolls onto shore.

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<v Speaker 1>When a plane flies passed its supersonic speeds, the exact

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<v Speaker 1>same thing happens, but instead of a large wake wave

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<v Speaker 1>from a boat, you get a sonic boom of sound

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<v Speaker 1>waves from an airplane. Be sure to check out our

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