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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

#51

Post by malingo »

Arjuna wrote: post #38
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,"

Speaking of the Saturn V... it's one of the most powerful machines that humans have ever created. It was equipped with five F-1 rocket engines, with each engine producing an absolutely staggering 1,500,000 pounds of thrust; that's a total of 7,500,000 pounds of thrust! Can you imagine being tucked into the small, cramped Command Module, sitting on top of this magnitude of power at lift-off? The whole thing, the techn…

Here is another video of the liftoff of Apollo 11 from one camera at the corner of the launch pad. Great narration too: http://vimeo.com/m/4366695

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

#52

Post by abduhl »

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…

I don't think this is correct. A sound wave propagates in three dimensions the same as an electrical field (spherically) and so should also obey the inverse square law.

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

#53

Post by malingo »

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…

Previous HN discussion about shuttle launches, with a very entertaining essay by Penn and Teller https://news.ycombinator.com/item?id=2793404

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

#54

Post by dkhar »

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…

Sound intensity actually falls off as 1/r², and here's a source:

http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.h...

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

#56

Post by femto »

abduhl wrote: post #52
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…

I don't think this is correct. A sound wave propagates in three dimensions the same as an electrical field (spherically) and so should also obey the inverse square law.

In this case, the atmosphere is essentially a thin (compared to the radius of the Earth) two dimensional sheet wrapping the Earth, so it's probably valid to think of the sound as propagating on a surface. There wouldn't be much loss of energy to space. Would the atmospheric interface with the ground reflect or absorb?

The divergence is probably even less that 1/r because the Earth is roughly sperical, and the sound will focus at the antipode of its source. There might even be a region, approaching the focus, where as the sound propagates its sound level is actually increasing, not decreasing!

It would be interesting to know what history has to say about Medellin, in Colombia, in 1883. Being at coordinates 6N 75E, it is roughly at the antipode of Krakatoa and could well have had an awful lot of energy dumped in it general direction a few hours after the eruption.

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

#57

Post by sillysaurus3 »

femto wrote: post #56
abduhl wrote: post #52

Earlier quoted context omitted.

I don't think this is correct. A sound wave propagates in three dimensions the same as an electrical field (spherically) and so should also obey the inverse square law.

In this case, the atmosphere is essentially a thin (compared to the radius of the Earth) two dimensional sheet wrapping the Earth, so it's probably valid to think of the sound as propagating on a surface. There wouldn't be much loss of energy to space. Would the atmospheric interface with the ground reflect or absorb? The divergence is probably even less that 1/r because the Earth is roughly sperical, and the sound w…

Would gravity affect soundwaves at all? If sound is traveling parallel to the Earth's surface, will it follow along the curvature of the Earth (implying gravity has an effect on it) or was it able to propagate around the Earth four times simply because the intensity was so great that it was able to still be heard despite the loss of energy in the "up-down" directions relative to the origin of the sound?

If I had to completely guess, I would think that gravity might have something to do with its behavior in this case, because if sound decayed at 1/r^2, it seems highly unlikely that the sound could survive four trips around the Earth. Yet we also have to explain how the sound was able to preserve itself even though sound travels "sort of spherically" (if you're up in the sky and someone shoots at you, you can hear it, so sound must be going up-down as well as left-right and every other direction) but if it was simply spherical in this case then it would decay into the upper atmosphere. If you imagine a sphere that grows from any point on the surface of the Earth, most of it will wind up in space, but since it circled the Earth, it must not have traveled exactly as sphere, which implies it didn't fall off as 1/r^2.

The most likely explanation seems to be that sound of huge intensity somehow follows the curvature of the Earth, which is very interesting. I wonder if gravity is influencing the soundwaves directly (which might actually be nonsense, since waves aren't matter, but something that travels through matter) or if gravity somehow sets up the propagation medium in a way that lets the sound curve around the earth without losing intensity as 1/r^2.

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

#58

Post by disillusioned »

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…

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 from the closest any humans are allowed to be (except for the brave rescue team in an APC 1 mile away).

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

#59

Post by sillysaurus3 »

dkhar wrote: post #54
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…

Sound intensity actually falls off as 1/r², and here's a source: http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.h...

If sound traveled as a sphere, then it wouldn't be able to circle the Earth. If you imagine a sphere growing from a point on the Earth's surface, most of it will wind up in space, and none of it will reach the opposite side of the Earth. The 1/r^2 falloff is probably just an approximation that holds true for short distances or smaller intensities.

In this case, the soundwave was able to follow the curvature of the Earth, which implies that it wouldn't decay as a sphere but rather a plane, which would be a 1/r falloff. I wonder why sound of massive intensity will follow Earth's curvature?

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

#60

Post by kruczek »

sillysaurus3 wrote: post #57
femto wrote: post #56

Earlier quoted context omitted.

In this case, the atmosphere is essentially a thin (compared to the radius of the Earth) two dimensional sheet wrapping the Earth, so it's probably valid to think of the sound as propagating on a surface. There wouldn't be much loss of energy to space. Would the atmospheric interface with the ground reflect or absorb? The divergence is probably even less that 1/r because the Earth is roughly sperical, and the sound w…

Would gravity affect soundwaves at all? If sound is traveling parallel to the Earth's surface, will it follow along the curvature of the Earth (implying gravity has an effect on it) or was it able to propagate around the Earth four times simply because the intensity was so great that it was able to still be heard despite the loss of energy in the "up-down" directions relative to the origin of the sound? If I had to c…

"which might actually be nonsense, since waves aren't matter, but something that travels through matter"

I don't think that's much of a nonsense. These are waves propagating through a medium - in this case mostly air. And particles of air are affected by gravity, therefore I would very much expect them to follow Earth's curvature.

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