Re: Re: Re: materials science
Compression results in the material occupying less volume. Compression can only occur when force is exerted from all directions or when the material is totally contained (preventing it from being displaced).
With the meager force applied by bending a strip of lead, you suggest the density of the lead will increase? Not likely. The side of the lead strip is not constrained in anyway and will displace outwards.
Yes, sound would not travel through it, neither would any other kind of kinetic energy.
In real terms it is impossible to completely contain anything for this test. No container will have infinitely stiff sides.
Andrew gave the example of the steel ruler being bent as an example of how easy it is to compress a material. I countered that by saying the metal is responding elastically and that the molecules are being displaced rather than compressed.
It's the displacement in the above examples that I'm talking about in terms of how water conducts sound.
Sound is a form of energy. It will excite the molecules it contacts by making them move. This movement is the transfer method through the medium. Efficiency of this transfer is dependent on the density and elasticity of the medium (determines speed of sound through the medium).
Sound energy will require the medium to expand in volume, as you cannot introduce energy to an open system without a volume increase. It is this increase in volume where the displacement by the energy transfer will show up.
So, same as the ruler, the water will be displaced rather than compressed.
Take a steel rod and heat the end. This is energy being introduced to the medium. The end of the steel rod that is being heated will expand. It expands because the molecules are moving more and need room to move.
It will contract as it cools, as the molecular movement returns to normal state.
Take a sealed can of soup and put it in an oven. Heat it up and take note of what happens. The walls of the can work to constrain the soups expansion but eventually the container fails.
Expansion of the liquid inside burst the can open.
despotic931 said:
Compression results in the material occupying less volume. Compression can only occur when force is exerted from all directions or when the material is totally contained (preventing it from being displaced).
With the meager force applied by bending a strip of lead, you suggest the density of the lead will increase? Not likely. The side of the lead strip is not constrained in anyway and will displace outwards.
despotic931 said:
Yes, sound would not travel through it, neither would any other kind of kinetic energy.
In real terms it is impossible to completely contain anything for this test. No container will have infinitely stiff sides.
despotic931 said:
Andrew gave the example of the steel ruler being bent as an example of how easy it is to compress a material. I countered that by saying the metal is responding elastically and that the molecules are being displaced rather than compressed.
It's the displacement in the above examples that I'm talking about in terms of how water conducts sound.
Sound is a form of energy. It will excite the molecules it contacts by making them move. This movement is the transfer method through the medium. Efficiency of this transfer is dependent on the density and elasticity of the medium (determines speed of sound through the medium).
Sound energy will require the medium to expand in volume, as you cannot introduce energy to an open system without a volume increase. It is this increase in volume where the displacement by the energy transfer will show up.
So, same as the ruler, the water will be displaced rather than compressed.
Take a steel rod and heat the end. This is energy being introduced to the medium. The end of the steel rod that is being heated will expand. It expands because the molecules are moving more and need room to move.
It will contract as it cools, as the molecular movement returns to normal state.
Take a sealed can of soup and put it in an oven. Heat it up and take note of what happens. The walls of the can work to constrain the soups expansion but eventually the container fails.
Expansion of the liquid inside burst the can open.
Re: Re: materials science
If not foolish, then arrogant, combative, and clueless.
Since you refused to actually comprehend the specifics of materials science... here it is...
Stress/strain are not both the result of applied force. One IS THE APPLIED FORCE, the other is the effect of that applied froce, both with specific meanings and definitions. Maybe you don't think this matters, maybe you don't understand the difference, who knows... but until you do, you really DO sound foolish.
You continue to ignore the particulars of this, making any "big brain" discussions impossible. If you can demonstrate you understand this difference, you'd be way ahead in making coherent arguments about properties of materials.
John L.
MJL21193 said:I've made through the dog days of August (my busiest time of the year) and I have some free time to get brow beaten and ridiculed again.
Really, do I look foolish? You "big-brained" fellows still refuse to discuss this intelligently (other than gtforme00).
Sy has yet to provide the evidence that he mentioned would be "trivially easy" to produce:
Yes, I'm serious.
Stress and strain are the result of applied force. Just like pressure is the result of applied force.
Look at the steel ruler as it flexes.
If not foolish, then arrogant, combative, and clueless.
Since you refused to actually comprehend the specifics of materials science... here it is...
Stress/strain are not both the result of applied force. One IS THE APPLIED FORCE, the other is the effect of that applied froce, both with specific meanings and definitions. Maybe you don't think this matters, maybe you don't understand the difference, who knows... but until you do, you really DO sound foolish.
You continue to ignore the particulars of this, making any "big brain" discussions impossible. If you can demonstrate you understand this difference, you'd be way ahead in making coherent arguments about properties of materials.
John L.
Re: Re: Re: materials science
No, the concept that when bent a metal strip will compress and not displace is rubbish.
I have had many opportunities in this thread and others to point out just how "arrogant" or "combative" or "clueless" some of you have been. I resist the temptation because I'm more courteous that that.
Please limit your comments to the topic and avoid the personal evaluation of my understanding, education or intelligence.
I'm here to discuss things reasonably, not listen to insults.
I will not bother to respond to any further posts that are insulting, whether they have relevant material or not.
I understand the difference between stress and strain. Stress is not an applied force - it is the result of applied force. Force begets stress, stress begets strain. Get it?
AndrewT said:
No, the concept that when bent a metal strip will compress and not displace is rubbish.
auplater said:
I have had many opportunities in this thread and others to point out just how "arrogant" or "combative" or "clueless" some of you have been. I resist the temptation because I'm more courteous that that.
Please limit your comments to the topic and avoid the personal evaluation of my understanding, education or intelligence.
I'm here to discuss things reasonably, not listen to insults.
I will not bother to respond to any further posts that are insulting, whether they have relevant material or not.
I understand the difference between stress and strain. Stress is not an applied force - it is the result of applied force. Force begets stress, stress begets strain. Get it?
I've resisted the temptation so far to contribute to this thread for two main reasons:
1) I don't feel qualified to comment on many of the ideas and concepts promoted, and am happy to learn from these contributions, and
2) I'm a proponent of lateral and alternative thinking - sometimes most of the world can be stuck in a rut, and it takes an unusal perspective to challenge the status quo.
However, I can't help stepping in here, and commenting that if you refuse to define your terms in the conventional way (or failing that, as a carefully expressed and specified alternative), constructive discussion is impossible.
Stress is DEFINED as force per unit area, so how can you possibly maintain that it is not an applied force? The definition insists that it is a force, and if not applied, how can it affect the system?
As 'your' stress is clearly a different concept from that generally accepted, can we therefore assume that some, if not all, of your other terms follow this rule? If so, your ideas may well be correct, but how could anyone tell, if they are expressed in meaningless (to the rest of us) terms?
1) I don't feel qualified to comment on many of the ideas and concepts promoted, and am happy to learn from these contributions, and
2) I'm a proponent of lateral and alternative thinking - sometimes most of the world can be stuck in a rut, and it takes an unusal perspective to challenge the status quo.
However, I can't help stepping in here, and commenting that if you refuse to define your terms in the conventional way (or failing that, as a carefully expressed and specified alternative), constructive discussion is impossible.
Stress is DEFINED as force per unit area, so how can you possibly maintain that it is not an applied force? The definition insists that it is a force, and if not applied, how can it affect the system?
As 'your' stress is clearly a different concept from that generally accepted, can we therefore assume that some, if not all, of your other terms follow this rule? If so, your ideas may well be correct, but how could anyone tell, if they are expressed in meaningless (to the rest of us) terms?
dnsey said:
Stress:
"Stress is a measure of the average amount of force exerted per unit area. It is a measure of the intensity of the total internal forces acting within a body across imaginary internal surfaces, as a reaction to external applied forces and body forces"
From the quickest Google search - Wikipedia.
Stress is not the force itself but the effect the force is having. Shear stress, compressive stress, tensile stress.
definitions
No, John... I'm not "right" here. Thousands of people much more intelligent than I have defined this so that they can converse intelligently about materials properties. But not you; apparently you want to redefine the entire field to suit yourself. Good luck with that
This is a definition. It's neither right or wrong... it's a definition. It's used to calculate and determine things, just as 1, 2, pi, j, those sorts of things.
But you don't want this to be true, so what's the point?
No, John... I'm not "right" here. Thousands of people much more intelligent than I have defined this so that they can converse intelligently about materials properties. But not you; apparently you want to redefine the entire field to suit yourself. Good luck with that
This is a definition. It's neither right or wrong... it's a definition. It's used to calculate and determine things, just as 1, 2, pi, j, those sorts of things.
But you don't want this to be true, so what's the point?
Let me get this straight. When I say that stress is the result of applied force, this is wrong? This is my own "interpretation" of the definition?
Gravity is a force. It exerts force of everything here on Earth. When a force comes to bear on an object, stress is developed. A stone laying on the ground is in compressive stress from the force of gravity.
A roof on a building is dealing with several stresses that are the result of the force of gravity. Compressive stress, tensile stress, torsional stress, shear stress, etc. All at the same time, from one source.
Force is not the same as stress.
Gravity is a force. It exerts force of everything here on Earth. When a force comes to bear on an object, stress is developed. A stone laying on the ground is in compressive stress from the force of gravity.
A roof on a building is dealing with several stresses that are the result of the force of gravity. Compressive stress, tensile stress, torsional stress, shear stress, etc. All at the same time, from one source.
Force is not the same as stress.
It's been your position all along and now you deny ever saying it? This is a direct quote from your first post:
Or how bout this gem?
So you did say it and you tried to justify it by making the semantic argument that the word "compression" can only be used to mean "reduction in overall volume". You claimed compression can't be the mechanism of sound transmission because the volume of the body of water isn't reduced, which is a silly word game that proves nothing.
If you really do know better and you're doing this to try to educate other people then please stop. Spewing a bunch of misinformation is not a responsible way to accomplish that goal.
Re: Re: Re: Re: materials science
I have a feeling that what you have just said will come back to bite you later, but here is my take on it. I'll start with an example, granted it has nothing to do with the argument at hand, but that doesn't seem to matter from what I gather...
Say we have a blacksmith, say he is heating that same steel rod that you just mentioned, and hammering it into a flat length (maybe for a sword or something, you get the idea). Anyways, you're going to have me believe that as his hammer comes down on that red glowing steel and crushes it against the anvil that there is no molecular compression taking place? I will agree that there is displacement, but that is only a part of what is going on. The same molecular elasticity that you keep bringing up is what causes the molecules to not remain compressed. I'll give you the fact that to compress something and make it remain compressed is extremely hard and requires a great amount of force, but causing momentary localized molecular compression of any medium is much much easier.
The same holds true for common air then I suppose? If contained in our imaginary container, under the pressure of 1 atmosphere, sound would not be able to travel through it even?
I think you missed his point, but thats ok.
Ummmm, ok, you should go and read this again... 1st hit on Google when you type "Sound in water" ...I say "again" because I'm sure you've seen it, but it seems like you've taken out the parts you want to hear, and forgotten the rest.
Good, that's an example of thermal expansion, really has nothing to do with sound waves. Now if I was real smart I'd start telling you that thermal contraction is evidence of compression, but there is already enough stuff that has been made up and taken out of context in this thread.
I'm sorry if I sound like my open mind is closing, but you've failed to prove to me that compression doesn't take place in a sound wave traveling through water. Now, after failing to prove it, you are claiming that you never claimed it. I expected that if you really believed what you said you would go down with your own ship John.
-Justin
MJL21193 said:
I have a feeling that what you have just said will come back to bite you later, but here is my take on it. I'll start with an example, granted it has nothing to do with the argument at hand, but that doesn't seem to matter from what I gather...
Say we have a blacksmith, say he is heating that same steel rod that you just mentioned, and hammering it into a flat length (maybe for a sword or something, you get the idea). Anyways, you're going to have me believe that as his hammer comes down on that red glowing steel and crushes it against the anvil that there is no molecular compression taking place? I will agree that there is displacement, but that is only a part of what is going on. The same molecular elasticity that you keep bringing up is what causes the molecules to not remain compressed. I'll give you the fact that to compress something and make it remain compressed is extremely hard and requires a great amount of force, but causing momentary localized molecular compression of any medium is much much easier.
MJL21193 said:
The same holds true for common air then I suppose? If contained in our imaginary container, under the pressure of 1 atmosphere, sound would not be able to travel through it even?
MJL21193 said:
I think you missed his point, but thats ok.
MJL21193 said:
Ummmm, ok, you should go and read this again... 1st hit on Google when you type "Sound in water" ...I say "again" because I'm sure you've seen it, but it seems like you've taken out the parts you want to hear, and forgotten the rest.
MJL21193 said:
Good, that's an example of thermal expansion, really has nothing to do with sound waves. Now if I was real smart I'd start telling you that thermal contraction is evidence of compression, but there is already enough stuff that has been made up and taken out of context in this thread.
I'm sorry if I sound like my open mind is closing, but you've failed to prove to me that compression doesn't take place in a sound wave traveling through water. Now, after failing to prove it, you are claiming that you never claimed it. I expected that if you really believed what you said you would go down with your own ship John.
-Justin
poptart said:
Compression to increase pressure in the medium without actual compression of the medium - this is what I have been saying.
Air is easily compressed, therefore it may well be compressed by a sound wave of sufficient energy. Since sound travel through air is the most relevant one, the "compression wave" label is less than perfect but it applies. Better to stick with the actual name - longitudinal wave.
Ever hear of a water compressor? How about a water pump? Have a look for diaphragm water pumps and see how they operate. Funny how they don't call these "water compressors", as they operate in an identical fashion to a sound transducer.
MartinQ said:
Well, your take on it, like auplater's, is incorrect. Stress is the effect the applied force is having on the object.
Do some reading.
Re: Re: Re: Re: Re: materials science
How will that come back to bite me? Read the definition of "compression".
Displacement is mainly what is going on. There is some local compression happening, a very small amount directly under the smith's hammer. This amounts to next to nothing though (yes, just like the compression that results from sound traveling through a liquid).
Interesting that you bring this up as it really drives home what I'm talking about here. The smith's hammer can pound a piece of metal into a thin sheet by displacement. This is exactly my point.
Applying your ideas, the smith's hammer would pound on the metal and the metal would respond by getting smaller, as it is compressed. Good thing that doesn't happen in the real world, right?
Air is easily compressed. A sound wave of sufficient energy will pass through this medium, even if it is contained.
Justin, you are working hard to miss every point. The counter arguments you put forth show some consideration of the ideas, but you fail to grasp what it is I'm saying here.
It isn't difficult or complicated.
despotic931 said:
How will that come back to bite me? Read the definition of "compression".
despotic931 said:
Displacement is mainly what is going on. There is some local compression happening, a very small amount directly under the smith's hammer. This amounts to next to nothing though (yes, just like the compression that results from sound traveling through a liquid).
Interesting that you bring this up as it really drives home what I'm talking about here. The smith's hammer can pound a piece of metal into a thin sheet by displacement. This is exactly my point.
Applying your ideas, the smith's hammer would pound on the metal and the metal would respond by getting smaller, as it is compressed. Good thing that doesn't happen in the real world, right?
despotic931 said:
Air is easily compressed. A sound wave of sufficient energy will pass through this medium, even if it is contained.
despotic931 said:
Justin, you are working hard to miss every point. The counter arguments you put forth show some consideration of the ideas, but you fail to grasp what it is I'm saying here.
It isn't difficult or complicated.
John, you appear to have conceded that compression does in fact take place when a longitudinal force is applied to a solid or liquid, be it lead or water or whatever. It seems however that you are still positing that this compression is unimportant and unrelated to any displacement that results. Your claim then being that displacement and sound travel can occur without any compression at all?
By what mechanism, then, does displacement occur when a localized force is applied? Displacement is not a force or mechanism itself as far as I understand, it is a vector giving the difference between two states of a system. If compression is not the mechanism, what is? Thermal? Electrical? Magnetic? Quantum? Can you explain your thinking here? As far as I can tell, either the molecules are compressed together and the material's elastic properties transmit the compression wave, or the force is instantaneously (hard definition) 'converted' to displacement (which is impossible thanks to relativity and common sense).
By what mechanism, then, does displacement occur when a localized force is applied? Displacement is not a force or mechanism itself as far as I understand, it is a vector giving the difference between two states of a system. If compression is not the mechanism, what is? Thermal? Electrical? Magnetic? Quantum? Can you explain your thinking here? As far as I can tell, either the molecules are compressed together and the material's elastic properties transmit the compression wave, or the force is instantaneously (hard definition) 'converted' to displacement (which is impossible thanks to relativity and common sense).
Re: Re: Re: Re: Re: Re: materials science
Well I'm glad I drove home what you were talking about, now if you could only re-read what you just said and understand it then we would be even!...
Or is this something that you will say, and then deny you said later?
I'm not working hard to miss anything John. Actually, I think I've probably worked the hardest out of all the people here to not miss any of your points! I have never said that displacement does not take place in any of the examples you've given (and you can actually go back and read everything I've written and see that that is true), but in my work to try not to miss anything I seem to notice that you've slipped away from your original point. Originally you had set out in this thread to prove that sound does not travel through water by compression. Now it just seems that you are out to prove something, anything, anything at all, just as long as it's something. Poptart's last post really drives how what I'm talking about.
Why do you ignore things you don't want to hear, and accuse others of doing the same?
I'm not telling you you're wrong, I'm telling you to get back to proving what you set out to prove! That is unless you don't believe it anymore...
-Justin
MJL21193 said:
Well I'm glad I drove home what you were talking about, now if you could only re-read what you just said and understand it then we would be even!...
MJL21193 said:
Or is this something that you will say, and then deny you said later?
MJL21193 said:
I'm not working hard to miss anything John. Actually, I think I've probably worked the hardest out of all the people here to not miss any of your points! I have never said that displacement does not take place in any of the examples you've given (and you can actually go back and read everything I've written and see that that is true), but in my work to try not to miss anything I seem to notice that you've slipped away from your original point. Originally you had set out in this thread to prove that sound does not travel through water by compression. Now it just seems that you are out to prove something, anything, anything at all, just as long as it's something. Poptart's last post really drives how what I'm talking about.
Why do you ignore things you don't want to hear, and accuse others of doing the same?
I'm not telling you you're wrong, I'm telling you to get back to proving what you set out to prove! That is unless you don't believe it anymore...
-Justin
uhm, ah,...Mongo is having trouble understanding just what this means...He gets hung up on there being a result (increase pressure) due to compression when compression is not present...if that is what you're saying, (and what you are saying IS changing as we go, tra--la-la--la-la) you are truly leading us through an exercise with too much wasted effort
Mongo knows if he hits a horse hard enough it will fall over, kinda empirical, ya know?
error401 said:
I have conceded nothing. I have always said that there is always some compression whenever a force is brought to bear, but that the amount of compression is so infinitesimally small, it does not figure as the main means of sound travel through a medium.
error401 said:
Displacement occurs when the molecules increase movement. They need room to move, and this is by displacement. I have cited examples earlier of how easy it is to displace water. It takes very little energy compared to compression.
The mechanism for energy transfer is kinetic. Energy from sound excites the molecules to a higher energy state (more movement). This energy is passed to the molecules in it's path by pushing. Given the density of water and the fact that it requires more force than is available from the sound wave to shorten the distance between molecules, the distance between molecules is not reduced (except for the infinitesimally small amount mentioned above). There is a loss of efficiency in the energy transfer, as the molecules in water are not lined up in a neat row. Water has low elasticity and the molecules, once moved, may not return to their original place.
Picture a thick (1/2" or so) layer of sand on a table. All of the grains are in contact with each other. Push your finger into the edge of the sand layer and see the energy transfer though the sand. It will not be transmitted directly to the other side of the sand layer, as there is lack of cohesion (elasticity) between the grains.
Instead, you will see displacement (in all directions).
Re: Re: Re: Re: Re: Re: Re: materials science
I've been saying the same thing all along. At an early stage I said that sound does not compress water. I still say that. The question is how sound travels through water, and this is by displacement, not compression. I said there is always SOME compression with applied force, but it does not have an impact on how sound travels. It's the same as saying that when I blink my eyelids, there is an effect on atmospheric conditions. My eye-blink has no notable effect on atmospheric conditions, but it's there and it happened just the same.
Put things in perspective. That will help.
Welcome back Ed,
Pressure is not the same as compression. What do you suppose the pressure would be at 100 metres below sea level if you were to dive there? How much more compact would the water be at that depth, considering it's only 1.8% more compact at the deepest part of the ocean, under thousands of metres of water?
Think about these things.
despotic931 said:
I've been saying the same thing all along. At an early stage I said that sound does not compress water. I still say that. The question is how sound travels through water, and this is by displacement, not compression. I said there is always SOME compression with applied force, but it does not have an impact on how sound travels. It's the same as saying that when I blink my eyelids, there is an effect on atmospheric conditions. My eye-blink has no notable effect on atmospheric conditions, but it's there and it happened just the same.
Put things in perspective. That will help.
Ed LaFontaine said:
Welcome back Ed,
Pressure is not the same as compression. What do you suppose the pressure would be at 100 metres below sea level if you were to dive there? How much more compact would the water be at that depth, considering it's only 1.8% more compact at the deepest part of the ocean, under thousands of metres of water?
Think about these things.
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