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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

#41

Post by Anechoic »

001sky wrote: post #39
Anechoic wrote: post #33

Earlier quoted context omitted.

Some of the newer non-lethal weapons the US military use for crowd control include a directional infrasound "gun" that basically vibrates your inner organs fast enough to make everyone super nauseous. Do you have a cite for this? A "directional" outdoor infrasound weapon would be huge (10s of feet) and quick web search seems to indicate these types of weapon are at best "not mature" and at worst fiction.

http://www.globalsecurity.org/military/systems/munitions/acc...

That article describes a theoretical infrasound weapon, not something that is being used today:

But this [infrasound weapon] has seemed to be not a very practical weapon, since large banks of speakers were required to provide directionality, and power demands were deemed excessive.

The article goes on to describe LRAD which does exist and has been deployed, but is a high-frequency weapon, not an infrasound weapon (and can be defended against with a good pair of earplugs).

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

#42

Post by gumby »

BrandonMarc wrote: post #15
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,"

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

Indeed; this is the principle behind the fire piston http://en.wikipedia.org/wiki/Fire_piston

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

#43

Post by th0ma5 »

One thing I only see a little bit about is the negative pressure pole created on the opposite side of the earth? I guess I need to spend some time at the library, but I've only seen this stated as a trivia item, but no further details, like was the effect as pronounced at that point given this is when the reflections outward all met up again?

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

#44

Post by post_break »

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…

Standing next to the thing makes you feel like an ant. I visit it once and a while and I just think to myself "we did this, this thing blasted off of the face of the earth with humans at the top"

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

#45

Post by [deleted] »

aatish wrote: post #12
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?

The sound was only audible up to 3000 miles in radius, or about 1/13th the globe. It wasn't audible in the other side of the Earth (although it was detectable.)

[deleted]

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

#46

Post by hmsimha »

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?

I suspect that due to variations in the earth's surface, and fluctuations in pressure due to things like air currents (and to a lesser extent perhaps even natural and man-made formations) the shock wave didn't travel uniformly in all directions, and wouldn't have been audible from the antipode.

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

#47

Post by jychang »

th0ma5 wrote: post #43

One thing I only see a little bit about is the negative pressure pole created on the opposite side of the earth? I guess I need to spend some time at the library, but I've only seen this stated as a trivia item, but no further details, like was the effect as pronounced at that point given this is when the reflections outward all met up again?

Sound doesn't travel at the same speed given different air pressures and temps. I think the waves wouldn't meet up at certain point.

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

#48

Post by [deleted] »

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…

[deleted]

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

#49

Post by ivansavz »

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 lines) and that total must be split over all possible directions. The total electric field must be split over the surface area of increasingly larger and larger spheres hence the 1/r² behaviour (1/4πr² to be precise). The sound energy is spread uniformly over a circle with circumference C=2πr, hence giving a 1/r decay, over short distances.

For longer distances, the curvature of the earth will play a role. Come to think of it, it must have been really loud somewhere diametrically opposite to Krakatoa, 17 hours after the eruption...

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

#50

Post by dingaling »

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…

> Speaking of the Saturn V... it's one of the most powerful machines that humans have ever created.

In the interest of completeness, here are the two most powerful launchers even flown in terms of first-stage lift-off thrust

N-1: 4,600 tonnes / 10 million lb

Energia: 3,600 tonnes / 7.9 million lb

Saturn V is currently in third place but will be pushed down if / when Falcon Heavy flies.

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