Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 21/04/2007 15:09:40
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Sound !!
It's very important....without sound I would not be able to enjoy the comforting click of each key as I depress them on my keyboard !...this is just one of quite a few advantages of sound !
Light... from which I understand,...... lasts forever until it hits something yes ?.........Well.........does not the same thing happen to sound !! ?...What has happened to the click of my keyboard depressions.....?..is it still traveling somewhere where someone could pick it up a year from now ?...
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I am not sure but seem to recall that sound does travel on for I don't know how long, bouning from one thing to the next.. like in a canyon when you hear that echo....the sound travling through the canyon... It is a great question where does it go ..Hee hee. That is interesting..
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Light only seems to last forever because our main light source (the sun) is so far away that it does not matter if the light has to travel one metre or one mile more or less.
It is different when you have only a candle (for example). You'll have (barely) enough light as long as you remain close to the flame, but the intensity of the light decreases as soon as you go farther away. In fact, the intensity is inversely proportional to the square of the distance; at twice the distance the intensity (per unit of surface illuminated) will be reduced to one fourth and so on.
It's the same with sound. Your ears are maybe about 50 cm from the keys on your keyboard, but if you move up to 5 m, the sound level of the click you hear will be already 100 times less.
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Light only seems to last forever because our main light source (the sun) is so far away that it does not matter if the light has to travel one metre or one mile more or less.
It is different when you have only a candle (for example). You'll have (barely) enough light as long as you remain close to the flame, but the intensity of the light decreases as soon as you go farther away. In fact, the intensity is inversely proportional to the square of the distance; at twice the distance the intensity (per unit of surface illuminated) will be reduced to one fourth and so on.
It's the same with sound. Your ears are maybe about 50 cm from the keys on your keyboard, but if you move up to 5 m, the sound level of the click you hear will be already 100 times less.
This Is wonderful ..ERIC IS GREAT !!
Thank you Eric....so....does the sound eventually dissipate into nothingness and can never be listened to again?
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I think there's a difference.
As light is an electromagnetic wave it can propogate in a vacuum and go a very long way... Look up at teh sky at night and some of those stars are thousands of light years away. There is of course a loss of intensity with distance, but stars avery very bright. Now consider a LASER beam shining up into space, it wouldn't see the same inverse square law for loss of intensity as it is a collimated beam - within the diffraction limit anyway. This is why it is possible to shine a beam at the moon and measure the reflected light. In theory a photon of light could go on 'forever' provided it didn't hit anything.
Sound is different. You hear sound beacuse of movement of air molecules. It is possible to focus sound to overcome the inverse square law but as a sound travels it will decrease in volume as the process of transmision of sound through a gas is 'lossy' - it is not 100% efficient. Eventually it will reach an intensity that is no greater than the random thermal vibrations and movement of the air molecules. At that point it is indistinguishable from heat and I think you can truly say it has faded to nothing. This will always happen. You can't transmit a sound in vacuum, and there will always be a gradual loss of intensity as ait travels through a gas, liquid or solid.
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I think there's a difference.
As light is an electromagnetic wave it can propogate in a vacuum and go a very long way... Look up at teh sky at night and some of those stars are thousands of light years away. There is of course a loss of intensity with distance, but stars avery very bright. Now consider a LASER beam shining up into space, it wouldn't see the same inverse square law for loss of intensity as it is a collimated beam - within the diffraction limit anyway. This is why it is possible to shine a beam at the moon and measure the reflected light. In theory a photon of light could go on 'forever' provided it didn't hit anything.
Sound is different. You hear sound beacuse of movement of air molecules. It is possible to focus sound to overcome the inverse square law but as a sound travels it will decrease in volume as the process of transmision of sound through a gas is 'lossy' - it is not 100% efficient. Eventually it will reach an intensity that is no greater than the random thermal vibrations and movement of the air molecules. At that point it is indistinguishable from heat and I think you can truly say it has faded to nothing. This will always happen. You can't transmit a sound in vacuum, and there will always be a gradual loss of intensity as ait travels through a gas, liquid or solid.
This is wonderful....BATROOST IS ALSO GREAT !! [;)]
So, Space is actually a very quiet place indeed !!..is it just air molecules that sound travels through ?..what about other gases ?
In fact are there other gases that would be an even better conduit for sound to travel through...ie: better clarity. ?..depth..?...volume ?...
Does this mean that when a big old star goes nova...it's as silent as my local library ?
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Sound (i.e. compression waves) will travel through any gas, solid or liquid - probably plasma as well though not really my field.
It's only really a vacuum that won't transmit a sound.
The denser a substance the faster sound will travel, so for example it travels about 10 times faster in steel than air.
As to how different molecules in the gas affect the transmission of the sound.... that's a really good question...! I'm guesing that lighter molecules are easier to move around (i.e. accelerate/decelerate) but then you might need to reduce the tempoerature to see teh affect as otherwise they'd be moving more quickly. As I said: good question!
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Sound (i.e. compression waves) will travel through any gas, solid or liquid - probably plasma as well though not really my field.
It's only really a vacuum that won't transmit a sound.
The denser a substance the faster sound will travel, so for example it travels about 10 times faster in steel than air.
This also explains how a stethoscope works : the sound is not propagated in an ever wider mass of air (or water or whatever) but in a rod or a tube of constant diameter. As it travels farther from the source, it does not spread out over a greater width. So, in a stethoscope it can retain its intensity, or at least most of it.
Other example : if you lay your head on a rail, you can hear the train coming over a very large distance, but not indefinitely. Every time the rail touches a sleeper (also known as "tie"), some of the sound is transmitted to that sleeper (and lost to the rail) and dissipates into the ballast.
As to how different molecules in the gas affect the transmission of the sound.... that's a really good question...! I'm guesing that lighter molecules are easier to move around (i.e. accelerate/decelerate) but then you might need to reduce the tempoerature to see teh affect as otherwise they'd be moving more quickly. As I said: good question!
You have an illustration when you inhale helium gas : you start speaking with a high pitched voice. There is a topic on that on this forum :
http://www.thenakedscientists.com/forum/index.php?topic=1036.0
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Sound (i.e. compression waves) will travel through any gas, solid or liquid - probably plasma as well though not really my field.
It's only really a vacuum that won't transmit a sound.
The denser a substance the faster sound will travel, so for example it travels about 10 times faster in steel than air.
As to how different molecules in the gas affect the transmission of the sound.... that's a really good question...! I'm guesing that lighter molecules are easier to move around (i.e. accelerate/decelerate) but then you might need to reduce the tempoerature to see teh affect as otherwise they'd be moving more quickly. As I said: good question!
THANK YOU BATROOST
I wonder how fast sound would travel through a piece of neutron star which is well dense !....so fast maybe that perhaps (if it were possible !!) one might conduct a conversation in morse code with someone on the other side of the star !
I also wonder if leaving one air molecule in a vacuum tube would be enough to propagate sound !
THANKs Batroost.
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hehehe frogs hhahaha sry random