Everything is compressible...
picture of my girlfriend
I'm a bit disappointed nobody else seems to have heard of Ice-9...
w
picture of my girlfriend
I'm a bit disappointed nobody else seems to have heard of Ice-9...
w
G.Kleinschmidt said:
to each his own
wakibaki said:
She is a big gal ain't she?
Hmmm, ice nine? Are we now going to question whether sound can travel through a fictional material?
MJL21193 said:
Too busy at the moment with work, but I'm not finished yet.
I'll be back.
I'll wait, but I am interested to hear your answers to my questions.
-Justin
Yeah, the Cat's Cradle stuff.
Just testing for some signs of culture as opposed to mere education.
All the physics argument earlier started me thinking about the phases of water, and its triple point. I was doing that in school about 40 years ago when I read the story, I can never think about the subject without thinking about Kurt Vonnegut and Cat's Cradle.
Some other, subtler characteristic of the argument reminded me of the book too...
It's a genuinely science-based, totally human work of fiction. If you haven't read it you're not really educated, never mind cultured.
Anybody read anything about programmable matter? Quantum dots?
w
Just testing for some signs of culture as opposed to mere education.
All the physics argument earlier started me thinking about the phases of water, and its triple point. I was doing that in school about 40 years ago when I read the story, I can never think about the subject without thinking about Kurt Vonnegut and Cat's Cradle.
Some other, subtler characteristic of the argument reminded me of the book too...
It's a genuinely science-based, totally human work of fiction. If you haven't read it you're not really educated, never mind cultured.
Anybody read anything about programmable matter? Quantum dots?
w
A sound wave is a density disturbance that travels through the medium. A knowledge of the manner in which this density disturbance is generated and how it propagates is fundamental to an understanding of acoustics and sonar.
In the simplest form, if we consider a point source in a homogenous medium, the sound waves emanating from it in all directions can be visualized as a series of expanding concentric spheres, the surface of which represent, at any instant of time regions of maximum compression. Midway between these regions there are zones in which the molecules are fully stretched. In both these areas sound in the form of the potential energy of the strain set up in the elastic medium. In changing from a state of compression to one of tension and back again, a state of maximum kinetic energy is traversed. This energy contained in the sound wave is constantly changing between potential and kinetic energy as it moves forward. For most purposes, it is convenient to consider this energy transfer process in terms of a sine wave. In this diagram the energy of the wave is proportional to the square of the maximum acoustic pressure or amplitude. (A) The intensity ( I ) is defined as the energy crossing a unit area at right angles to the direction of propagation per unit time measured in Hz. The speed ( C ) is related to frequency ( f ) and wavelength ( / ) by the expression C = f / (something missing here)
One other important concept is the phase angle, which is defined by the point on the curve reached by the wave at any particular moment. When two different signals are in phase, their amplitudes add algebraically or reinforce each other; when 180 degrees out of phase they are subtracted; and in between these two limits the combined amplitude is the vector sum.
...from a bathymetry handbook
Don't ask anything more, I don't know where this book is, right now.
Only thing I can add is, this handbook was supplied with an echosounder made by a highly reputed military equipments' manufacturer
In the simplest form, if we consider a point source in a homogenous medium, the sound waves emanating from it in all directions can be visualized as a series of expanding concentric spheres, the surface of which represent, at any instant of time regions of maximum compression. Midway between these regions there are zones in which the molecules are fully stretched. In both these areas sound in the form of the potential energy of the strain set up in the elastic medium. In changing from a state of compression to one of tension and back again, a state of maximum kinetic energy is traversed. This energy contained in the sound wave is constantly changing between potential and kinetic energy as it moves forward. For most purposes, it is convenient to consider this energy transfer process in terms of a sine wave. In this diagram the energy of the wave is proportional to the square of the maximum acoustic pressure or amplitude. (A) The intensity ( I ) is defined as the energy crossing a unit area at right angles to the direction of propagation per unit time measured in Hz. The speed ( C ) is related to frequency ( f ) and wavelength ( / ) by the expression C = f / (something missing here)
One other important concept is the phase angle, which is defined by the point on the curve reached by the wave at any particular moment. When two different signals are in phase, their amplitudes add algebraically or reinforce each other; when 180 degrees out of phase they are subtracted; and in between these two limits the combined amplitude is the vector sum.
...from a bathymetry handbook
Don't ask anything more, I don't know where this book is, right now.
Only thing I can add is, this handbook was supplied with an echosounder made by a highly reputed military equipments' manufacturer
wakibaki said:
"Why don't you just make 10 louder?" is the question asked in the movie, see here...
Spinal Tap Scene
Anyways, back on the original subject. According to John's theory would it not be nearly impossible for sound to travel through water at great depths? I am assuming this due to the extreme pressure already exerted near the ocean floor.
Portlandmike said:
wakibaki said:
Once again, I didn't say that water in incompressible. Everything is compressible, under the right conditions.
despotic931 said:
It's not how I think it travels, it's how I know it travels.
Here's the point: Water that is subjected to less than 1GPa of pressure is treated as incompressible.That is to say that 1 gigaPascal of force needs to bear in order to effect a notable change in density in water at a fixed temperature. That's a lot of force.
Acoustic sound waves can be measured in the uPa range - that's microPascals. This is an insufficient amount of force to compress water.
To compress anything, it needs to be in a closed system - no matter can escape from any direction. If force from a sound wave is brought to bear on water that is not in a closed system, matter will be pushed out. No compression will result, just displacement.
Sound waves produce areas of high and low pressure within a medium. This is the result of excitation of the molecules (increased motion) from the positive portion of the wave. The negative portion of the wave creates a low pressure region (reduced motion). Pressure is not the same as density. Pressure is force. Force in this case is kinetic energy moving through the water.
Still a couple questions,
Is this how sound travels through all mediums, or is water just an anomaly?
Have you thought about shock compression? I believe I mentioned it earlier.
I think you need to come to terms with the idea that there isn't displacement without compression. Even if I put my hand in a swimming pool, and push it forward displacing the water, for a split second before the water is displaced there is an amount of compression.
-Justin
Is this how sound travels through all mediums, or is water just an anomaly?
Have you thought about shock compression? I believe I mentioned it earlier.
I think you need to come to terms with the idea that there isn't displacement without compression. Even if I put my hand in a swimming pool, and push it forward displacing the water, for a split second before the water is displaced there is an amount of compression.
-Justin
despotic931 said:
For the most part, in most circumstances, sound energy will displace rather than compress in all mediums.
Shock waves are the product of a rapid rise in pressure, temperature or density. This has little to do with the propagation of sound through a medium in the usual sense. A couple of good examples of shock wave in water are Tsunami (you can drown in the displaced water) and "water hammer" - this is what you hear in some household plumbing pipes when you turn off the faucet quickly. A loud banging sound. Pipes have broken from this increase in pressure. The way to tame it is to have trapped air in the pipes in a few places. Air, unlike water, is easily compressed and will absorb the pressure increase.
What the rest of you need to come to terms with is the primary mechanism for sound transfer through water is displacement.
There is always some compression with applied pressure, I know this, BUT this is NOT how sound travels through water.The amount of compression that that results from sound waves traveling through water is unmeasurable - it's practically non-existent due to the small amount of force involved.
It goes back to what I've been saying all along: it takes a lot less force to move something as opposed to crushing it - displacement rather than compression.
MJL21193 said:
This observation is just "trivia" (and not in anyway a contribution to the debate). I haven't read all the posts so this might have been mentioned already but the first page got me thinking of an interesting experience I had over 40 yrs ago when I was about 10/12 yrs old.
We were on holidays and standing ankle deep in a mountain stream with a hard rocky bottom. I guess the water varied in depth between 4" and 15". We were throwing stones upstream and they were travelling 30 or 40 yards. They were probably between an egg and a tennis ball in size. I can clearly remember hearing the stones hit the rocky bottom of the stream before hearing the sound of the splash as the stone broke the surface of the water. I can recall being intrigued by the phenomenon but just knew enough science to think that the sound was travelling through the rocks under the water faster than through the air. I hadn't thought of the water as the medium.
We were on holidays and standing ankle deep in a mountain stream with a hard rocky bottom. I guess the water varied in depth between 4" and 15". We were throwing stones upstream and they were travelling 30 or 40 yards. They were probably between an egg and a tennis ball in size. I can clearly remember hearing the stones hit the rocky bottom of the stream before hearing the sound of the splash as the stone broke the surface of the water. I can recall being intrigued by the phenomenon but just knew enough science to think that the sound was travelling through the rocks under the water faster than through the air. I hadn't thought of the water as the medium.
I could honestly come to terms with the fact that there is some displacement taking place, but I have yet to be convinced that it is the primary mechanism for sound transfer.
If sound was carried through water by displacement, then the sound wave would easily transfer from the water to the air above as it was displaced by the water. Instead in real life sound does not pass easily from one medium to another. Ever been under water and had someone yelling at you from the surface, it's hard to hear them. Or been above the water while someone under water makes noise, it's hard to hear them too. All I'm saying is that if sound was transmitted by displacement it would have a much easier time passing from one medium to the next, especially from a denser medium to a low density medium (under water to above water). Think of listening to a train track with your ear pressed up against it for an oncoming train. If the sound was traveling down that track via displacement then it would reverberate into the surrounding air much more efficiently than it does. Compression and the density of the metal used in the track allows that sound to travel long distances down it, but it does not make for a very efficient transfer of the sound wave from the track to the surrounding air.
-Justin
If sound was carried through water by displacement, then the sound wave would easily transfer from the water to the air above as it was displaced by the water. Instead in real life sound does not pass easily from one medium to another. Ever been under water and had someone yelling at you from the surface, it's hard to hear them. Or been above the water while someone under water makes noise, it's hard to hear them too. All I'm saying is that if sound was transmitted by displacement it would have a much easier time passing from one medium to the next, especially from a denser medium to a low density medium (under water to above water). Think of listening to a train track with your ear pressed up against it for an oncoming train. If the sound was traveling down that track via displacement then it would reverberate into the surrounding air much more efficiently than it does. Compression and the density of the metal used in the track allows that sound to travel long distances down it, but it does not make for a very efficient transfer of the sound wave from the track to the surrounding air.
-Justin
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