Compression of water (split from Waveguides)

[Ed LaFontaine]

the substance under given conditions

...is the qualifier you are overlooking...the given conditions are not absolute, they can change...and when that happens the characteristics of the material, including density, can change.

You are explaining yourself clearly...your conclusions are incorrect.

At the 4*C point in water at standard pressure, molecules are not moving

Says who?

Where is there any supportive argument in the literature for what you are concluding ?




edit: clarify

[y8s]

Originally posted by MJL21193
One glitch: What happens when you release the pressure? It will return to steam of course.
When I said the temperature needs to drop for water to be in a liquid state, I did mean at normal pressure.

Temperature and pressure both change when you release the steam.

look at a can of compressed air--you know, those "electronics dusters". Or even a propane tank. both have highly compressed gases to the point where they are liquid (no temp changes, they are stored at room temp)

if you quickly release the gas, what happens? pressure inside the can drops fast and the can is rigid so volume can't change to accomodate the pressure change. net result: the can gets COLD.

pressure drops inside the can and temperature drops to catch up with the pressure drop.

then after a short while, temperature re-equalizes with the room temperature and the can's internal pressure rises again.

you could do this with water if it was a gas at room temperature too.

[MartinQ]

Originally posted by MJL21193
At the 4*C point in water at standard pressure, molecules are not moving.

Ohhhh ... they certainly are moving. They will continue to do so until the energy level drops to 0 at around −273.15 °C (0 K). It's not until absolute zero when matter finally goes to sleep.

Originally posted by MJL21193
So, that is why I say there is no real compression, just displacement.

If there is any compression, then I'm afraid it is very real. If sound travels through water, then the water has been compressed and expanded as the wave passes through.

[hpasternack]

Under the circumstances, I think you're been treated pretty well, John. To your credit, you've shown you're willing to back up and ask questions. Maybe there's hope for you yet.

In my opinion, you're making this too complicated. It should be good enough to use the balls-and-springs analogy here. What you are saying is that for water, in its (not it's) liquid state, the springs between the balls are infinitely stiff. It follows that if you line up a series of balls and springs and push on the ball at one end, then the ball at the other end will start moving instantaneously. If this is true, then this represents transmission of information at infinite speed, something we ought to agree is impossible.

The thought experiment of the line of molecules extending from Earth to Proxima Centauri is just an extreme way to illustrate the point.

If, on the other hand, we concede that it takes some time for the displacement wave to travel from one end of the sample to the other, then it must be that in the interim the sample has been compressed -- one end moved, but the other didn't.

Since most of the space inside a volume of water is vacuum, you might want to ask yourself what the mechanism is that transmits the force from one molecule to another. Then research the properties of that force and understand why it acts more like a spring than like a perfectly rigid rod.

-Henry

[MJL21193]

Originally posted by Ed LaFontaine


...is the qualifier you are overlooking...the given conditions are not absolute, they can change...and when that happens the characteristics of the material, including density, can change.

You are explaining yourself clearly...your conclusions are incorrect.

Keep an open mind:
The medium is at 4*C, standard pressure - this is the condition before sound. When sound starts to move through it, it changes density and temperature. It only stands to reason that the excitation of molecules from the energy of the sound wave will increase temperature from friction. With this temperature change, you will see a density change, as density will decrease as temperature rises.
Energy from the sound wave is being dissipated in the medium - this produces heat.
For the above, the medium could be at any constant temperature or pressure. Injecting energy from a wave source produces movement which in turn produces heat from friction. Heat will increase temperature, density will lower.
How is this conclusion incorrect?

[MJL21193]

Originally posted by y8s



Temperature and pressure both change when you release the steam.

The idea was that steam will compress back to water without a temperature drop. I think that when you relese the pressure on the compressed water, given that there wasn't a temperature drop, it will revert to steam. My point is that in order for steam to condense into water, its temperature needs to drop.

Originally posted by MartinQ


Ohhhh ... they certainly are moving. They will continue to do so until the energy level drops to 0 at around −273.15 °C (0 K). It's not until absolute zero when matter finally goes to sleep.

That really doesn't matter. Energy into a system produces heat. Heat will effect a density decrease. Please read my reply to Ed - I'm getting tired of typing the same thing over and over.

Originally posted by MartinQ

If there is any compression, then I'm afraid it is very real. If sound travels through water, then the water has been compressed and expanded as the wave passes through.

You sound very sure of yourself. You being on the "right" side of the discussion makes that acceptable.

[MartinQ]

Originally posted by MJL21193
Please read my reply to Ed - I'm getting tired of typing the same thing over and over.

Awesome! I'm starting to feel the same way.

Originally posted by MJL21193
You sound very sure of yourself. You being on the "right" side of the discussion makes that acceptable.

I'm not sure what you're getting at or how to read this. Please enlighten me.

[scott wurcer]

Sorry if I missed this already posted, but this is my favorite resource on wave propagation in solids vs liquids vs gasses. Unfortunately a couple of the equations have broken links now but almost everything is there.



http://hyperphysics.phy-astr.gsu.edu.../sprop.html#c1

[Ed LaFontaine]

from post 95:

How is this conclusion incorrect?

I think you conclude from reading the word "maximum" that it describes a condition for density not to be exceeded. It can be exceeded when the standard conditions change. The presence of sound waves is not part of "standard conditions"

When sound starts to move through it, it changes density and temperature.

Injecting energy from a wave source produces movement which in turn produces heat from friction.

You conveniently omit the compression resulting from the passage of the sound wave.

The passage of a sound wave is not one sided. The density fluctuates from the high side to the low side of "standard pressure" in cycles.

Be careful, you have almost admitted to the compression of water by using those statements.

I'm getting tired of typing the same thing over and over.

Your fatigue stems from your dogged determination to avoid the conventions the majority of us are at peace with...it is a result of choices you make yourself...not something thrust upon you.

[MJL21193]

Originally posted by hpasternack

in its (not it's) liquid state

Maybe I would have only .01 posts per day if I were to proof read all of my contributions with the same vigor as you read yours. I do pretty good considering.
BTW, I know the difference between its and it's, but thanks for the corrective email and the lesson anyway.

Originally posted by hpasternack

Under the circumstances, I think you're been treated pretty well, John. To your credit, you've shown you're willing to back up and ask questions. Maybe there's hope for you yet.

The circumstances being that I don't agree with you? This is reason to be harsh?
I'm glad that you feel there is hope for me, and I am impressed that you have "compressed" your posting frequency down from 1 in a hundred days to voice your thoughts here.

Originally posted by hpasternack

What you are saying is that for water, in its (not it's) liquid state, the springs between the balls are infinitely stiff.

Not what I said at all actually.

Originally posted by MartinQ

I'm not sure what you're getting at or how to read this. Please enlighten me.