# Shock waves faster than the speed of sound? (explosion question)

**URL:** <https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855>\
**Category:** Factual Questions\
**Created:** [July 22, 2009, 2:26pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855 "2009-07-22T14:26:25Z")\
**Posts on this page:** 11\
**Page:** 1

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**Author:** ![cgg419](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cgg419/32/2847_2.png) [@cgg419](https://boards.straightdope.com/u/cgg419)\
**Post date:** [July 22, 2009, 2:26pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/1 "2009-07-22T14:26:25Z")

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I just heard a brief sound, the whole apartment building shook, and then a second or two later, I heard what sounded like an explosion.

There is a quarry just down the road, although in living/being in this town part time for 20 years I’ve never heard anything similar.  
Did somebody just set off a bomb?

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**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\
**Post date:** [July 22, 2009, 2:29pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/2 "2009-07-22T14:29:53Z")

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Noise travels through earth and stone faster than through air.

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**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\
**Post date:** [July 22, 2009, 2:48pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/3 "2009-07-22T14:48:41Z")

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**Quartz** has correctly described what you experienced.

However, shock waves can go faster than the speed of sound of the medium, but it has to be a truly large release of energy for the shock to be supersonic at a distance.

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**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\
**Post date:** [July 22, 2009, 4:53pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/4 "2009-07-22T16:53:20Z")

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> [@Quartz](#):
>
> Noise travels through earth and stone faster than through air.

> [@Pleonast](#):
>
> **Quartz** has correctly described what you experienced.

Figures **Quartz** would know. 😃

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**Author:** ![cgg419](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cgg419/32/2847_2.png) [@cgg419](https://boards.straightdope.com/u/cgg419)\
**Post date:** [July 22, 2009, 5:38pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/5 "2009-07-22T17:38:34Z")

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I appreciate the responses, but for a layman (that is slightly embarassed that he doesn’t quite understand)…does that mean I did or did not hear an explosion? 😕 :smack:

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**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\
**Post date:** [July 22, 2009, 6:19pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/6 "2009-07-22T18:19:41Z")

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Don’t be embarrassed to ask for more detailed explanations. That’s the whole point of the SDMB. 🙂

Here is what happened:

1. Explosives are detonated in the quarry.
2. The energy not used to break rocks propagates out in the form of sound waves.
3. The sound travels at the speed of sound in the medium its in. The speed of sound through the earth is something like ten times greater than the speed of sound through air.
4. The sound traveling through the earth reaches you. Since your ears are in air, you can’t hear this sound. Instead, you feel it and the secondary vibrations created by it.
5. Finally the sound traveling through the air reaches you.

So, in simple terms, you felt the explosion first (because sound propagates through earth very fast) and then you heard the explosion later.

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**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\
**Post date:** [July 22, 2009, 6:24pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/7 "2009-07-22T18:24:32Z")

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But as the sound travels through the earth, the ground and objects can be disrupted enough to make their own sound(s). You might feel \*\*and \*\*hear something prior to the full, air-carried sound wave finding its way into your head, where you ears and brain work to translate it into a sound.

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**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\
**Post date:** [July 22, 2009, 6:55pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/8 "2009-07-22T18:55:32Z")

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> [@Philster](#):
>
> But as the sound travels through the earth, the ground and objects can be disrupted enough to make their own sound(s). You might feel \*\*and \*\*hear something prior to the full, air-carried sound wave finding its way into your head, where you ears and brain work to translate it into a sound.

So is it right to say that the “brief sound” as the apartment shook was the equivalent of the cup-n-string telephone? That is, s/he heard the apartment (the cup) transmitting the sound through the Earth (the string)?

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**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\
**Post date:** [July 22, 2009, 7:12pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/9 "2009-07-22T19:12:37Z")

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Yes

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**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [July 22, 2009, 7:16pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/10 "2009-07-22T19:16:42Z")

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Nitpick: Shock waves are by definition supersonic. It doesn’t usually travel far though, as **Pleonast** said. In most situations where you get to hear a “shock wave” (e.g. explosive going off at a survivable distance, or a supersonic aircraft passing overhead), the shock wave loses energy and becomes a normal sound wave before it reaches you.

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**Author:** ![cgg419](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cgg419/32/2847_2.png) [@cgg419](https://boards.straightdope.com/u/cgg419)\
**Post date:** [July 23, 2009, 1:11pm UTC](https://boards.straightdope.com/t/shock-waves-faster-than-the-speed-of-sound-explosion-question/503855/11 "2009-07-23T13:11:16Z")

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Ignorance fought.  
Thanks everybody 🆒