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The Sound So Loud That It Circled the Earth Four Times

nautil.us

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Re: The Sound So Loud That It Circled the Earth Four Times

#71

Post by DanBC »

dandelany wrote: post #28
jbert wrote: post #5

Nice. I hadn't thought of there being a limit (due to vacuum) to sound intensity. Reminds me of this recent comment on reddit: http://np.reddit.com/r/space/comments/2h9y9g/the_first_launc... "the Saturn V rocket produced a SWL (Sound Power Level) of about 220 decibels, which is sufficient to melt concrete nearby and set grass aflame a mile away,"

Yes! My favorite example of this is the sound made by the space shuttle's solid rocket boosters at liftoff. Techies who have seen recordings of shuttle launches generally assume the guttural crackling, popping roar sound they hear is due to a badly adjusted microphone clipping the loud sounds. In fact, this was a physical phenomenon that could be heard in real life, due to the pressure waves physically "clipping" aga…

Is this brap noise like "cavitation" you get from propellors in water?

Re: The Sound So Loud That It Circled the Earth Four Times

#72

Post by marcosscriven »

disillusioned wrote: post #58
dandelany wrote: post #28

Earlier quoted context omitted.

Yes! My favorite example of this is the sound made by the space shuttle's solid rocket boosters at liftoff. Techies who have seen recordings of shuttle launches generally assume the guttural crackling, popping roar sound they hear is due to a badly adjusted microphone clipping the loud sounds. In fact, this was a physical phenomenon that could be heard in real life, due to the pressure waves physically "clipping" aga…

I had the privilege of watching STS-134 launch from the press site and everyone tells you: "it's loud. louder than loud. you will be surprised by how loud it was." and that still wasn't enough to prepare me. It is loud. It is literally like the sound is clipping, the brapping noise moves through your teeth, it vibrates your clothes, you feel it inside of you. It is incredible, and I was so lucky to have watched it fr…

I recall being thrilled to be able to see STS-124 in May 2008, only because the previous launch had been delayed, and the new date coincided with our holiday. Among other things it was taking up parts to fix a toilet on the ISS!

I remember also being struck by not only how loud it was, but also how bright. It's something that photos or video just can't capture.

Re: The Sound So Loud That It Circled the Earth Four Times

#73

Post by gambiting »

josu wrote: post #19
jbert wrote: post #5

Nice. I hadn't thought of there being a limit (due to vacuum) to sound intensity. Reminds me of this recent comment on reddit: http://np.reddit.com/r/space/comments/2h9y9g/the_first_launc... "the Saturn V rocket produced a SWL (Sound Power Level) of about 220 decibels, which is sufficient to melt concrete nearby and set grass aflame a mile away,"

But the article says: "This limit happens to be about 194 decibels for a sound in Earth’s atmosphere." Therefore, wouldn't 220db be like -280°C? EDIT: Somewhat of an answer: 194.09(P) = 1 (ONE) AIR ATMOSPHERE = 14.6962 POUNDS PER SQUARE INCH = 14.6962 P.S.I.= 1 ATM SOUND WAVES DISTORT AND ARE NOW DEFINED AS SHOCK WAVES AND THEY BEGIN TO FOLLOW SHOCK WAVE BEHAVIOR. PARTICLE VELOCITY (BLAST WIND) = 590 FEET / SECOND =…

-280C would be -7 Kelvin, and therefore impossible.

Re: The Sound So Loud That It Circled the Earth Four Times

#74

Post by pcrh »

ivansavz wrote: post #49

Interestingly, the sound intensity will decay as a 1/r law, where r is the distance from the source. (I'm assuming conservation of sound energy as it travels horizontally, i.e., no loss to interactions with atmosphere and terrain). Compare with the 1/r² laws like the strength of an electric field at a distance r from charge Q: E(r)=kQ/r². In both cases there is a total of something (sound energy or electric field lin…

The antipode of Krakatoa is Bogotá, Colombia. I wonder what the news reports from there said at the time?

Re: The Sound So Loud That It Circled the Earth Four Times

#75

Post by sillysaurus3 »

jonsen wrote: post #68
sillysaurus3 wrote: post #65

Earlier quoted context omitted.

Nah, imagine a point on the earth. Now trace rays from that point in every possible direction. All of those rays will eventually lead to space or to the ground, and none will reach the other side of the Earth. Since molecules are physically further apart the higher you go in the atmosphere, it seems unlikely that the energy would be redirected at the edges, only dispersed. That must mean the wave is literally followi…

Sound waves can diffract around objects, which is why one can still hear someone calling even when hiding behind a tree. : http://en.m.wikipedia.org/wiki/Difraction

Is diffraction the reason why soundwaves could travel around the whole Earth? My previous understanding of diffraction was that obstacles cause waves to propagate in different ways. But the thinning of the atmosphere isn't really an "obstacle." The molecules that soundwaves use to propagate are simply further apart from each other, meaning waves are more likely to disperse and lose energy than to keep traveling or bounce. That would imply the boom from the volcano should disperse into space and go silent rather than travel around the Earth. But since that doesn't happen, it seems like the waves follow wherever the atmosphere is thick.

I'm having trouble understanding how diffraction would cause that end result of "waves go where the atmosphere is." If waves could bounce off of the thin atmosphere near space, that would make total sense. But they can't bounce due to thin atmosphere, only disperse, so it seems like there's some other phenomenon in play.

Re: The Sound So Loud That It Circled the Earth Four Times

#76

Post by jonsen »

sillysaurus3 wrote: post #75
jonsen wrote: post #68

Earlier quoted context omitted.

Sound waves can diffract around objects, which is why one can still hear someone calling even when hiding behind a tree. : http://en.m.wikipedia.org/wiki/Difraction

Is diffraction the reason why soundwaves could travel around the whole Earth? My previous understanding of diffraction was that obstacles cause waves to propagate in different ways. But the thinning of the atmosphere isn't really an "obstacle." The molecules that soundwaves use to propagate are simply further apart from each other, meaning waves are more likely to disperse and lose energy than to keep traveling or bo…

Sound waves are points of high pressure and points of low pressure. At each point of high pressure the pressure tends to spread uniformly in all directions. Likewise at points of low pressure there is sucking from all directions. Opposite directions cancel, i.e. orthogonal to the wave direction. All in all the sum of all points of pressure creates a moving wavefront. Which naturally bends around obstacles. The earth is just a very big obstacle.

Re: The Sound So Loud That It Circled the Earth Four Times

#77

Post by aruggirello »

marcosdumay wrote: post #22
BrandonMarc wrote: post #15

Earlier quoted context omitted.

Wait, the sound caused the grass to catch fire?!

A 220 dB sound is quite strong. As an example, its intensity (in W/solid angle) is 14 orders of magnitude (AKA 100 billion times) highter than the 80 dB people usualy use as a safety limit.

Are you sure? Shouldn't a 140 dB difference in intensity equate to just about 2^14, hence 16384 times stronger?

Re: The Sound So Loud That It Circled the Earth Four Times

#78

Post by junto »

pcrh wrote: post #74
ivansavz wrote: post #49

Interestingly, the sound intensity will decay as a 1/r law, where r is the distance from the source. (I'm assuming conservation of sound energy as it travels horizontally, i.e., no loss to interactions with atmosphere and terrain). Compare with the 1/r² laws like the strength of an electric field at a distance r from charge Q: E(r)=kQ/r². In both cases there is a total of something (sound energy or electric field lin…

The antipode of Krakatoa is Bogotá, Colombia. I wonder what the news reports from there said at the time?

I would assume that energy follows the path of least resistance. Hence, all the energy went up and out and not down.

Notably Bogota sits in a huge valley, so they are also less likely to have been affected by the surface sound wave as well.

Re: The Sound So Loud That It Circled the Earth Four Times

#79

Post by junto »

rspeer wrote: post #32
danielweber wrote: post #11

So the sound got harder to hear as you were farther away, but what if you were at the exact antipode on Earth? Would it have been audible at all?

Something that makes this extra intriguing: the exact antipode of Krakatoa seems to be in an inhabited area on the banks of the Rio Magdalena in Colombia. I wonder if anyone was there at the time to notice a pressure wave coming from all directions.

Its in a huge valley if that has any bearing.
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