Hi MJ,
can you compress water with the force of your hands?
I can compress steel with the force available to my little pinkie.
Try this experiment:
pick up a steel rule, six or 12 inch, it matters not.
Now clasp one end and hold it out horizontally. Use your pinkie to apply a little force to the other end. Press down. The steel rule bends. Try a lighter force, it still bends.
Clamp the rule in a vice. How light a force can you apply and still see the deflection due to the rule bending?
What is happening to the rule while you have been bending it?
One side has been compressing (getting shorter) and the other side has been extending (getting longer).
You have been compressing Steel with the tiniest forces your finger can provide.
Water is even more compressible than steel. Try to find an experiment that shows how compressible. Ah! transmit sound, that should do it.
can you compress water with the force of your hands?
I can compress steel with the force available to my little pinkie.
Try this experiment:
pick up a steel rule, six or 12 inch, it matters not.
Now clasp one end and hold it out horizontally. Use your pinkie to apply a little force to the other end. Press down. The steel rule bends. Try a lighter force, it still bends.
Clamp the rule in a vice. How light a force can you apply and still see the deflection due to the rule bending?
What is happening to the rule while you have been bending it?
One side has been compressing (getting shorter) and the other side has been extending (getting longer).
You have been compressing Steel with the tiniest forces your finger can provide.
Water is even more compressible than steel. Try to find an experiment that shows how compressible. Ah! transmit sound, that should do it.
/sreten.
Wunderland
Looks like Alice is still mired in the rabbit hole... it's amusing how the anti-compression argument spirals 'round and 'round.
Such an extraordinary set of claims should be viable for the Nobel prize in physics, were it to survive peer review after publication, one would think.. eh?
John L.
Looks like Alice is still mired in the rabbit hole... it's amusing how the anti-compression argument spirals 'round and 'round.
Such an extraordinary set of claims should be viable for the Nobel prize in physics, were it to survive peer review after publication, one would think.. eh?
John L.
MJL21193 said:
A SONAR transducer in its most simple form is a puck of ceramic material. We pot these inside of epoxy housings for various reasons, but the essential function of the bare puck can suit our discussion.
Maybe this gif will work:
By applying a very high voltage (thousands of volts) to either metallized surface of the puck, the puck will elongate in shape, like a bipole source. Yes there will be some displaced fluid that "wraps around" the sides of the transducer and cancels out the pressure difference (hence defining the directivity of the transducer). However not all of the displaced molecules will be able to make trip around the sides to equalize the pressure. These molecules will have to be compressed into the adjacent fluid forming a pressure wave.
Keep in mind that the displacements we are talking about are on the micro-inch scale. It doesn't take much of a relative difference in pressure to result in a very large SPL. An underwater SPL of 140 dB (1 uPa reference) will only require 10 Pa (0.00145 psi) of increased pressure.
More important than the amount of displacement or the pressure required is the time aspect of this example.
No signal, whether physical or electrical can travel faster than the speed of light, which is itself finite. If we displace some molecules at the ocean floor and they are hundreds of meters from the surface, the time it takes to displace the molecules at the surface must be a some time other than zero (when the first molecules were displaced). In order for this to occur, there must be compression somewhere in the system until the pressure signal has time to pass through the medium.
Another interesting example would be to consider a long rigid pipe that is full of water. If a valve is opened at the entrance to the pipe, it is required that there be some non-zero amount of time before the water at the exit of the pipe moves in response to the inrush at the valve. I would submit that there must be compression of the water in this circumstance as well.
Replace the valve in the above example with a SONAR transducer. I could place a ceramic puck of equal diameter to the inside diameter of the pipe in the entrance of rigid pipe of water. If I excite this transducer and produce a displacement of the transducer, the water cannot wrap around the sides of the transducer and a plane wave will travel in the water towards the exit. This displacement cannot occur at all places in the water simultaneously or it will violate the speed of light limit, so it travels as a pressure (compression) wave towards the open end of the pipe, the speed at which it travels is the speed of sound.
Regards,
David Malphurs
sreten said:
Once again, I didn't say that water is inelastic. How many time do I need to say this? Water has elasticity. Got it?
AndrewT said:
Hi Andrew,
Nice analogy, but not an accurate one. Compression and tension in your example are stresses and strains. There isn't compression (density increase) of the metals structure in your example.
This is elasticity at work and a good example of it. The bending of the steel ruler deforms the crystal structure of the metal by (you guessed it) displacement.
A text on elasticity will explain it in depth.
gtforme00 said:
Hi David,
displacement of water is very easy. Imagine a bathtub. Now the given is that the rim of the bathtub is perfectly level and it is filled with water up to the rim. You slowly put your hand in the water near one side and see what? Water spills from the entire tub, not just from where you've put your hand in.
Now, that's a large displacement with little effort. Millions of molecules were displaced. Get the picture?
Your tube example is an interesting one, but the time lag involved for the water to shoot out of the exit with be very small indeed. Remember, I'm not saying that water is incompressible, just that sound waves travel through a medium primarily by displacement. I have acknowledged that some very slight compression takes place, but it does not factor in as the means of energy transfer.
The transducer in your example would act like a pump and setting the water in motion, not the molecules themselves (although some still may). This is flow (forward and back), not a true sound wave.
contrarian, with a touch of certainty
A contrarian is someone who poses as a skeptic, refusing to accept consensus conclusions in science on the ground that there is still some uncertainty.
...some text deleted...
Contrarians often refer to their endless demands for more study and their claims that doubts still remain—no matter what the consensus—as "sound science," a bit of doublespeak that is the scientific equivalent of the filibuster.
...from another one of those searches.
A contrarian is someone who poses as a skeptic, refusing to accept consensus conclusions in science on the ground that there is still some uncertainty.
...some text deleted...
Contrarians often refer to their endless demands for more study and their claims that doubts still remain—no matter what the consensus—as "sound science," a bit of doublespeak that is the scientific equivalent of the filibuster.
...from another one of those searches.
MJL21193 said:
You mean like, if I push on a spring that's attached to a ball, and the ball moves, then the spring does not factor in in the energy transfer?
It's true, none of the energy is peranently stored in the spring any more than the molecules remain permanently crowded, but to suggest that either does not factor (participate) in the energy transfer is to deliberately close your eyes to the reality. How else can the energy be transferred other than via the mutual repulsion of the electrons in their orbitals?
If you are saying that the compression is small compared to a molecular diameter, well and good, but it is mischevous to attempt to subvert the compression model of the process, since it permits meaningful predictions which are only obfuscated by your position.
w
I don't know why this discussion (which should have been the simplest of all time) got to me so much but I just couldn't leave it alone without asking an expert to confirm we're not all taking crazy pills. I'm leaving the man's name out of this because it was gracious enough of him to answer an unsolicited email from me. The last thing I want to do is drag him into this. but he's a professor at an american university and one of his areas of expertise is underwater acoustics.
this is my email and his response:
So what do you know, sound compresses water and this is how sound propagates. In case you missed it the very first thing the man said was
"Water is compressible. Sound propagates by a compression wave."
can this be over now?
this is my email and his response:
So what do you know, sound compresses water and this is how sound propagates. In case you missed it the very first thing the man said was
"Water is compressible. Sound propagates by a compression wave."
can this be over now?
John, I'm fascinated by your insistence on spelling "its" with an apostrophe, even though you know by now that adding the apostrophe makes a different word entirely.
-Henry
[Edit: It's interesting to note that the professor in poptart's message just above makes the same mistake. Hmmm. What is the world coming to?]
-Henry
[Edit: It's interesting to note that the professor in poptart's message just above makes the same mistake. Hmmm. What is the world coming to?]
wakibaki said:
Everyone deserves to be heard with an open mind. However it is only the week minded who open their minds and believe what is poured into them on simply a whim.
poptart said:
I'm sure there are those that would like it to end, but I fear that John will never succeed his theory to the truth. Also, not only do I find this thread entertaining, it is also educational!
hpasternack said:
If we look at the length and topic of this thread it seems to be just as baffling...
MJL21193 said:
Hi,
I see. Pop at the only the thing you can and ignore the rest.
Utterly tedious. I'm now getting to the point were I believe you
are simply being belligerent and have no interest in the actual
subject. All you are interested in is your facetious arguments.
So there is no point continuing this "discussion".
/sreten.
despotic931 said:
I am sure that your position is motivated by a sense of fairness and egalitarianism, unfortunately these are no more proof against the self-deluded than the dissembling (e.g fascism). Sometimes a more militant approach is thrust upon us. Sometimes we need to have confidence in what we consider reasonable to the extent that we can firmly reject views that we know are not. John's use of language has been extremely devious, hence we need to be extremely forthright.
Peter Aczel said:
Quoted slightly out of context - he's more concerned with the 'subjectivist' position in this comment - but in my opinion the time for open minds is long past here.
w
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