Howdy Borys Kapochkin,

"... the general (universal) physically justified and understandable regularity of wave attenuation ..." Yes!

Doing science needs different rules from using science. That past work has found a correlation between acoustic frequency and propagation distance in water is valid statistics and a usable observation, but like many other issues in the history of science useful does not explain. "... the theory of the process of absorbing the energy of acoustic waves in water ..." is needed to "do science." Excellent!

Your discussion of the dependence of propagation on wave type is important. The capillary and gravity waves on the surface of water due to the wind have very different internal dynamics from earthquake response of a tsunami. Energy absorption, and resulting propagation distance, is determined by the medium response to the wave presence and must be considered, as you note.

There is a "bottom line" tendency in humanity that is valuable for efficient living and improving life experiences. This "if it works, that is good enough" mentality spreads over science where it must be opposed, as you have done here. Rigor, not just useful, is essential to provide valid results "to be used." Good show!

Happy Trails, Len

Dear colleagues.

For more information see the preprint "REGULARITY OF THE WAVE ENERGY ABSORPTION PROCESS AS AN EXAMPLE OF THE PROPAGATION OF ACOUSTIC WAVES IN WATER". The authors of the idea (article) are interested in supporting publication in a specialized scientific journal outside of Ukraine.

Sincerely, Borуs.

For bending wave propagation in concrete and maybe gypsum boards, the loss factors follow a 1/f^1/2 trend indicating less loss per cycle at higher frequencies than at the low. This is a SEA empirical result eg published by Craik.

For propagation in air it is temperature and RH (relative humidity) dependant with higher losses for the high frequencies. The frequency region of highest loss is dependant on the RH. The effect is clear enough to be audible in a larger auditorium if the climate changes from low RH to high, on the reverberation times.

I am not an expert on underwater sound propagation. But I ca enaough to say that it is very complicated due to layering, channeling from layering (can also happen in air) giving far less losses than for an expected omnidirectional propagation (all energy shared equally in 3D). Other factors that matters are bubbles, waves or not, seabed absorption, the degree of diffusion of reflections and temperature gradients. The noise floor is also an issue in all detection, so near ice it is noisy. Sea living creatures may also make noise.

In general reverberation times are higher in the lows supporting your idea, but it is way more complex than that.

Dear Anders Buen,

Your information on less attenuation of high frequency waves in concrete is very important. In seismoacoustics, low-frequency waves are used for greater scanning depth.

You write about the propagation of sound in gases (in air). I think moist air can be thought of as a mixture of gas and liquid. The speed of sound in water is 1500 m/s and in air 330 m/s. In water, infrasound travels thousands of kilometers, but much less in air.

You wrote about hydroacoustics. The topic of discussion is the range of sound propagation in a waveguide. Bubbles, bottom sediments, waves on the surface are other processes. They reduce the range of infrasound from thousands of kilometers to 5 kilometers.

Sincerely, Boris.

Under water layering effects can make shadows or the sound propagation simply is refracted or deflected back. If the reflection is strong enough, the propagation will not go further, just back, or in another direction. I guess this is also an issue for seismic waves. The distance a sound can go is dependant on the source strength, the transfer path properties and the noise level at the receiver. Under water, we have reverb, like we have in rooms. Reverb will also limit the ability for the receiver to get useful information out of the signal, if any is left. At least in our fjords with limited size, that is an issue. I think it is in the north sea and Eastern sea as well, as the seabed is quite near the surface.

5 km in general sounds optimistic, under very good conditions with channeling, strong sources, it may be hundreds of km (I do not know the literature numbers here). There is literature out there on the possibilities of detecting and get useful information out of submarine activities. e.g. it is not a simple task and the conditions changes with time.

It is my frank opinion that Mr. Borys Kapochkin is wrongly discussing about the "sound propagation in the ocean" without knowing the very basic knowledge of sound propagation in a media, let it be water!..... He did not take care in defining the input sound energy and its frequency contents first. They are most important aspects for the long distance sound wave propagation in ocean under turbulent conditions.

The very basics points in my understanding are the followings:-

1. Beam divergence, dispersion, attenuation, etc. are the inherent properties of sound irrespective of any media.

2. Attenuation is the causes of all losses of sound energy, including losses due to divergence, dispersions, reflection, refraction, etc.

3. Sound attenuation increases with its frequency.

4. It is really foolish to discuss the propagation of transverse wave propagation in ocean and that to for long distance. Water can only hold and propagate longitudinal (pressure or compressional) waves.

5. Another foolish thing is to discuss the Sunami", the water waves of surface waves under this topic of "sound wave propagation in the ocean"....! Concepts of Boyle's Law is more appropriate to discuss and to understand about tsunami water waves with dispersive and diversive natures.

Dear Palanichamy Perumal. To your answer, framed in an insulting form, I will answer with the famous saying of Socrates (this is an ancient Greek philosopher). Quote: "I know that I know nothing. But others know even less." I think you understood that the last phrase concerns you personally. In the topic of the discussion, I expressed doubt that the statistical relationship between the range of sound propagation and the frequency of an acoustic wave is not identical to the statement that there is a causal relationship between the frequency of the emission of a wave and the range of its propagation in water. I hope you understand this subtle difference. You have written many different words. For example, I learned from you that the range of sound propagation depends on turbulence. I was very surprised. I know about dynamic and kinematic viscosity, but I don't know about turbulence as an argument for calculating the sound propagation distance. If this is not an error, please provide a link to the formula for the sound propagation distance, where there is turbulence (Richardson and Reynolds criteria) or at least fluctuations in temperature, salinity, ... The second time I was surprised when I learned from you that the range of sound propagation in water depends on the divergence. I have a question about the divergence of what? On Wikipedia I found the definition "In physical terms, the divergence of a vector field is the extent to which the vector field flux behaves like a source at a given point". Divergence is considered only in relation to flows, not waves. In waves, the mass is not transferred, which means that there can be no divergence of the flow. If you are truly competent, back it up with facts. The third time I was surprised when I learned from you that the range of sound propagation in water depends on the sound dispersion. DISPERSION - dependence of the phase velocity of waves on frequency. Dispersion is not included in the sound damping equations. If you are truly competent, back it up with facts. And finally, I know for sure that transverse waves propagate far beyond the boundaries of their source of excitation and tsunamis are no exception. "TSUNAMI - marine gravitational waves of very large length, are transverse waves" https://studbooks.net/1857490/matematika_himiya_fizika/tsunami_poperechnye_morskie_gravitatsionnye_volny. We have had a very pleasant conversation for me. I thank you, Boris..

Howdy Borys Kapochkin,

I also find it pleasant to read all about acoustic propagation and find information in these replies that is interesting, although subject to validation as you have noted. I shall find it even more pleasant to read a reply that addresses your observations:

"for the entire frequency range of acoustic waves, the range of their propagation, measured not in units of measurement of distance, but in cycles, is a constant;" and

"In the topic of the discussion, I expressed doubt that the statistical relationship between the range of sound propagation and the frequency of an acoustic wave is not identical to the statement that there is a causal relationship between the frequency of the emission of a wave and the range of its propagation in water."

Science discovers, engineering uses, manufacturing applies. In Science, correlations be damned! - except as crutches for the present or as guides to comprehending the natural process behind the correlation in the future.

The heart of my earlier reply is here: a discussion about how acoustic attenuation in water occurs in view of the results in your report would be welcome.

Happy Trails, Len

Mr. Borys Kapochkin, "I know that I know nothing. But others know even less."......I do know where you got this!.... But according to me it conveys that we are in the same boat of "knowing nothing" and we are discussing about the great subject of "sound propagation in the ocean"...... Let us continue.....!!!!.....

I have written "Beam divergence, dispersion, attenuation, etc. are the inherent properties of sound irrespective of any media."

For this you have written that "sound propagation in water depends on the divergence".......This is somewhat confusing statement and to the extent wrong also.

It is just that "sound beam divergence occurs due to the propagation of sound in the medium".

Again, DISPERSION - dependence of the phase velocity of waves on frequency..... And everybody knows about this!....And also wrote that "The third time I was surprised when I learned from you that the range of sound propagation in water depends on the sound dispersion."

What I what to convey is DISPERSION occurs during the sound propagation in any media and not that "sound propagation in water depends on the sound dispersion." The main cause of dispersion in any media is scattering. And the wave-wave interference also contributes to some extent to the dispersion of sound waves..

Dispersion is frequency dependant wave velocity. Sound in water is not dispersive. The ocean waves are dispersive.

I propose to discuss the data on wind waves. This is a preprint of "REGULARITY OF THE PROCESS OF ABSORPTION OF ENERGY OF WAVES ON THE EXAMPLE OF THE PROPAGATION OF LONGITUDINAL (SOUND) AND TRANSVERSE (SURFACE) WAVES IN WATER".

What is the difference between longitudinal (acoustic) waves and transverse (wind) waves in water? Acoustic waves have practically no dispersion. The speed of sound in water is the same for almost the entire frequency range and is determined only by density (the total mass of molecules and their associations) and compressibility. Phase velocity, wavelength and wave period are constant. As the wave propagates in water, only the energy of the wave (acoustic pressure) changes. Transverse (wind) waves in water are characterized by dispersion с=√(gλ/2π). Ensuring the constancy of the frequency of transverse waves is realized by changing the length and phase velocity of the wave. It is important to note that the wave height, as a characteristic of its energy, is not included in the equations for calculating the phase velocity, period, and angular velocity of the wind wave. Usually, the wave height is associated with the radius of the particle's orbit in the wave https://search.rsl.ru/ru/record/01006934294. Obviously, acoustic and wind waves have significant differences. We analyzed the known facts about the attenuation of transverse (wind) waves with depth. With increasing depth, the radius of the particle's orbit, like half the height of the wave, decreases in accordance with the well-known empirical formula in which the argument is the frequency of the wave https://search.rsl.ru/ru/record/01006934294. Because of this, researchers may also get the wrong impression about the frequency dependence of the shear wave attenuation. It has been established (https://search.rsl.ru/ru/record/01006934294) that a wave with a cycle length of 10 m at a depth at a depth of 1 cycle (10 m) will be 0.002 of its height at the surface; a wave with a cycle length of 100 m at a depth of 1 cycle (100 m) will also be 0.002 of its height at the surface and a wave with a cycle length of 1000 m at a depth of 1 cycle (1000 m) will be 0.002 of its height at the surface. Conclusion. The process of attenuation in water of more complex transverse waves is identical to the process of attenuation of simpler longitudinal waves. See preprint. "REGULARITY OF THE WAVE ENERGY ABSORPTION PROCESS AS AN EXAMPLE OF THE PROPAGATION OF ACOUSTIC WAVES IN WATER". Sincerely, Boris.

First let us clear some doubts over the terminologies being used in studying the Propagation of Sound Waves in solids, liquids and gases...

The word "Acoustics" is a general term and it constitutes all frequencies and all types of Bulk (longitudinal and transverse) waves and types of Surface (Rayleigh, Lamb, Stonley, etc.) waves.

Acoustic wave frequency is an important factor and through which one can classify the acoustic waves as Sub-sonics (0-20 Hz), Sonics Or Sound waves (20 Hz to 20 kHz), Ultrasonics (above 20 kHz) and upto 1000 kHz, Hypersonics (above 1000 kHz), etc.

Water or tidal waves and even tsunami waves comes under the Sub-sonics side.....

It is my understanding that during propagation of acoustics wave in any medium beam divergence and wave dispersion inherently occur due to the reason that the generated or the propagating acoustic/ sound waves are not coherent.. From all the above discussions it is known that attenuation of sound waves during its propagation is ocean could be easily understood. Whereas the term dispersion of wave (frequency dispersion) during its propagation in ocean could not be understood as easily as wave attenuation....

Frequency dispersion could be easily observed when ultrasound travel trough a polycrystalline medium. But while considering the acoustic wave propagation in ocean scattering, wave-wave interaction, interference, etc. are not being considered. Or the contribution due such factors are comparatively very small and hence not being taken into account experimentally, I suppose.

Errata: "Ultrasonics (above 20 kHz) and upto 1000 kHz, Hypersonics (above 1000 kHz), etc." must be read as

"Ultrasonics (above 20 kHz) and upto GHz, Hypersonics (above GHz), etc.".....

Dear Palanichamy Perumal. I think that it is advisable to correct your words about terminology in accordance with reliably known facts. For example, you have assigned to sound types of waves that are not moving in the volume of the compression front. Think of a thesis involving coherence. Waves are characterized by the invariance of frequency with distance from the source. Read carefully about the refraction of sound and the spatial inhomogeneity of the sound velocity field. And finally, about your final thesis... The process of the absence of sound dispersion in water has no clear physical explanation. The process of wave attenuation in water does not have a clear explanation, since the theoretical calculations of the range are tens of times higher than the measurements. For water, the Newton-Laplace formula (calculation of the speed of sound) cannot even be used, which works for other media. In this case, your statement that "dispersion of wave (frequency dispersion) during its propagation in the ocean could not be understood as easily as wave attenuation...." is analogous to saying that two to the power of zero is greater than one to the power of zero. Sincerely, Boris Kapochkin.

Dear Borys Kapochkin, I think that we are discussing something in which we are interested or in which we know something to some extent.....

I am a Physicist with Materials Science background and you seems to be Oceanographic expert. First what was confused me was that the sentence "sound propagation in the ocean has a correlation with frequency" . Now I understand that you only deal with sub-sonic (less than 20 Hz) acoustic wave propagation in ocean. I have really not worked anything with that type of sound wave propagation in ocean. But during 2004 I have really experienced the effect of tsunami at Kalpakkam, India. Please continue with your fruitful discussions. All the best....Palanichamy

You are absolutely right. Hydroacoustics is the most unexplored field of acoustics. The military does not allow the dissemination of knowledge in this area. Training in hydroacoustics, as a part of physics, is not carried out in civilian universities, but only in military research centers and enterprises. I'm not saying it's bad. This is reality.

Howdy Borys Kapochkin and Palanichamy Perumal,

Your recent clarifications and accommodation are very welcome.

Borys has reported research results that led to his inquiry in two questions that I have seen on ResearchGate about the physics of acoustic wave propagation in the ocean, specifically its relation to wavelengths. Now, “it is known that” the attenuation varies with frequency according to correlation results, however, any correlation of acoustic waves with frequency must be accompanied by an inverse correlation with the wavelength of those waves. His reported results show:

The distance of sound propagation in the ocean has a correlation with frequency. . .. Maybe it's a false correlation?

He clarifies his concern with his discussion, namely, “The results of our research determined for the first time that for the entire frequency range of acoustic waves, the range of their propagation, measured not in units of measurement of distance, but in cycles, is a constant: the same number of cycles corresponds to the same absorption of acoustic energy.”

He expressed a valid concern! Correlations may guide research that discovers a valid cause and effect relation, but the correlation may be due to another factor instead of the true cause, therefore he asks:

What is the physics of this phenomenon?

Personally, I would like to know the answer to this question. We have been treated in these threads to extensive information about wave propagation in oceans and air, which I appreciate because I enjoy learning, however . . .

I also have hoped with other ResearchGate questions that someone learned would treat us with a clear answer, and in lieu of that have offered a possibility which might evoke such a response. That approach worked for tropical cyclones with very helpful references provided by Janusz Pudykiewicz that repaired my speculation, so we try again and offer for consideration the following: (please pardon the declarative format, it is convenient in this speculation)

While water is incompressible for many engineering and approximate scientific uses, water does not know about that. It is a fluid of molecules and molecular clusters with sufficient unoccupied volume to allow compression and sufficient activity (molecular unrest) to fill an entire volume subject to the gravitation constraint for a liquid. When the compression is due to kinetic energy, which must be finite, the potential energy gradient of a compression reaction brings the motion to a halt, like a pendulum rising against the acceleration of gravity. Gradient of that potential energy reaction acts to accelerate fluid into a kinetic energy phase, the whole process repeats and is termed a wave, say an acoustic wave in our case. The directed motion of the kinetic energy phase determines the direction of continuing kinetic -> potential -> kinetic energy exchanges and the wave propagates. But you all know about this.

Molecular unrest is very efficient, however, and exchanges occur in water continually among energy forms due to collision, molecule spin and molecular internal oscillations. Per Huygens insight, the waveform radiates from each point and leads to curvature of the wavefront at its “ends” and eventually along its whole surface, weakening the intensity but not directly losing energy. Refraction and reflection also redirect energy without necessarily losing it. The temporal and spatial resolution of molecular unrest is much finer than these macroscopic happenings and resolves them precisely.

According to the research result cited by Borys, the attenuation of the studied acoustic waves was identical for each cycle regardless of frequency. This implies to me that the hybrid digital-analog computer of molecular unrest in water was capable of calculating energy exchanges more rapidly than they were occurring, thus rates of exchange (frequency) did not disturb the process. Also, it implies that the molecular unrest computer was capable of calculating energy changes over full wavelength distances without distance limitation in the process. (For air the molecular unrest performs 10^35 operations per second per cubic meter at STP. I was unable to find the equivalent value for sea water – it would be welcome.)

Now, given the range of fluid states between kinetic and potential energy extremes in a propagating wave, it is suggested that attenuation of energy occurs through slight randomization of the molecules during the cycles sufficient to account for the losses per cycle. The randomized motions would appear as heat.

Valid, rigorous, convincing, etc. are not claimed here, these are just thoughts that ring true enough to me to risk expressing them. “To know” is more elusive.

Happy Trails, Len

Dear Leonard Hall, We really appreciate your scientific assumptions, which force us to be creative. It is also difficult for me and my colleagues to imagine the physics of the same absorption of energy in a cycle with a spatial extent of 10 m and in a cycle with a spatial extent of 10 cm. In a wave, when a molecule moves at different distances within different cycle lengths, different work A = F * L is performed, which means that a different amount of energy must be spent. This suggests at least two options. The first option: in a short cycle, the work performed is less, and in a long cycle, more. But this has not been confirmed in practice (short waves attenuate more than long ones). The second option: the length of the path of the molecule in the wave cycle is the same for all wavelengths. Perhaps this is observed in a conductor with an alternating electric current (a wave is generated without mass transfer?). The electron path length is fixed and extremely small. In direct current, which can be analogous to flow (mass is transferred), energy losses are thousands of times greater. Conceptually, it sounds like this: THE PHYSICS OF SHAPE TRANSFER IN A WAVE IS CARDINALLY DIFFERENT FROM THE PHYSICS OF MASS TRANSFER IN A DIRECTIONAL FLOW. Perhaps this analogy has some meaning? Sincerely, Boris.

Howdy Borys Kapochkin,

"In a wave, when a molecule moves at different distances within different cycle lengths, different work A = F * L is performed, which means that a different amount of energy must be spent."

Ahhh! but in the oscillations of a waveform the energy is not "spent," it is "invested" with a nearly 100% return. If the molecular unrest implementing the oscillations is very much "faster" or "has longer reach" than the oscillations they will be treated alike, whether 10 cm or 10 m. The distance of individual molecule movement is sufficient to implement the movement of the wave, which is much longer than the molecular motions.

A third option: the bulk response of wave propagation by molecular unrest is equally efficient over the wavelength range considered in your research and the losses are due to a partial randomization of the molecules in the invest-return economics of the kinetic potential energy transformations. Attenuation is about energy leaking from the oscillations rather than being about the work performed within them.

Happy Trails, Len

According to the "classical" theory, the attenuation of sound in water occurs as a result of friction and the transfer of wave energy into internal energy, into heat. Sound attenuation is explained by the viscosity of water. The greater the viscosity, the greater the absorption of sound wave energy.

It is stated that the speed of sound in water does not depend on the viscosity, but depends on the elasticity of the water. Viscosity and elasticity are different concepts. But in the formulas for calculating the coefficient of dynamic viscosity, viscosity is associated with the parameters of the state of sea water (temperature, salinity and pressure). In the formulas for calculating the speed of sound, the elasticity of water is also associated with the parameters of the state of sea water (temperature, salinity and pressure). I think that the complex of inconsistencies and contradictions is obvious.

We have not touched upon the topic of differences in wave propagation in compressible and incompressible fluids.

We have not considered the issue of wave transfer of its form. There are no questions for wind surface waves. For sound, the question of transferring the form is ...

This is not the whole list of questions to the "classical" theory of sound attenuation in water.

How to come to an understanding of the physics of the process of sound attenuation in water? The authors of the preprint REGULARITY OF THE WAVE ENERGY ABSORPTION PROCESS AS AN EXAMPLE OF THE PROPAGATION OF ACOUSTIC WAVES IN WATER cut the "Gordean knot" of these problems. Quote: "The expression "cut the Gordian knot" means to find a non-trivial, bold and simple solution to a complex, confusing issue." The theory of these authors works. There is no understanding of the mechanism. This problem must be solved.

Howdy Borys Kapochkin,

Excellent! From the classical theory: the attenuation of sound in water occurs as a result of friction and the transfer of wave energy into internal energy, into heat. This words well my communication attempt in : the losses are due to a partial randomization of the molecules in the invest-return economics of the kinetic potential energy transformations.

Classical: It is stated that the speed of sound in water does not depend on the viscosity, but depends on the elasticity of the water. Of course! The kinetic theory of fluids includes the awareness (assumption?) that individual molecular exchanges are loss free. Viscosity occurs through randomization of coordinated motion, say of a wave, causing loss of energy from that motion. The transmission of sound must be by the coordinated motion which is carried on despite escape of a few molecules. It is carried on by kinetic potential energy transmission, thus elasticity, not viscosity. It's actually not that hard - as we have agreed "science is simple."

"inconsistencies and contradictions" are sourced in an effort to explain with insufficient understanding and/or inappropriate analogs. The heat produced during sound energy attenuation is not due to surface friction like screeching tires in a panic stop, it is a consequence of slight randomization of the molecules involved in passing along the coordinated motion of waves such that those molecules no longer contribute to the wave motion and their randomized motion is read as heat.

I appreciate this opportunity to think this through to this understanding. If your reference does it better that's fine with me and better for other readers.

Perspective on molecular events and classical interpretation: "latent heat." "Latent heat" is convenient, but the nature of thermal energy in evaporation - vapor transport - condensation is lost in the impression the term leaves. During evaporation of water, for the most part energetic (fast) molecules escape the liquid surface. During condensation of water vapor, for the most part low energy (slow) molecules are captured. Evaporation cools a surface because "hot" molecules leave while condensation heats the air because "cool" molecules leave the air to arrive at the liquid. "Latent heat" is a convenient, but misleading, term to account for this process by stating in its definition that "latent heat" is "transferred" during the process. Bosh! Since the "cool" molecules leave the air "to arrive" in the liquid, the air surrounding a condensation site is left with higher average molecular energy and therefore "appears" to have been "warmed." "Latent heat" is only a convenient fiction. [Please, do not let this personal realization confuse the sound attenuation issue, I add it because it also offers an alternative to convenient wording of phenomena and may clarify the kinetic theory background. I've not yet seen it elsewhere.]

Alexander agreed that it was a quite complex knot holding that chariot at Phrygian Gordium, but a sword "cuts through" it easily enough, and there was a world to be conquered - like phenomena to be explained. Good addition!

Happy Trails, Len

Howdy Borys Kapochkin,

I have written up part of our above discussion on your questions Maybe it's a false correlation? and What is the physics of this phenomenon? about the research results you have cited on acoustic propagation in the ocean. My write-up includes a quote from J. Frenkel's Kinetic Theory of Liquids and separates items in your replies from my speculations. As a contribution to exploration and discovery, I like it this way, but someone else may read it so you should know I did it and request improvements you would like. This version does communicate better. It can be found on my project, Whence Insight, on my site here on ResearchGate. It is Thoughts on Acoustic Wave Propagation and Attenuation in the Ocean and a *.docx file is attached there.

This has been an example of learning and experiencing an insight through discoveries in our exchange and belongs on "Whence Insight" as an illustration. Please request changes of portions that may lead to negative feedback for yourself.

Happy Trails, Len

Dear Leonard Hall. In your text, the problematic issue of the physics of evaporation from the water surface is touched upon. I specialized in the surface layer of water and I know for sure that the physics of evaporation is still not clear. The classical explanation that "During the evaporation of water mostly energetic (fast) molecules escape from the surface of the liquid" always seemed fantastic to me. After all, it is known (measured) that water has a huge surface tension due to the peculiarities of its molecular structure (the dipole moment of the H2O molecule) and its result - hydrogen bonding, which are specifically manifested in the skin layer of water at the boundary between the ocean and atmosphere phases. In order to overcome this natural barrier, under the conditions of the Earth's gravity directed in the opposite direction of the movement of the "energetic" molecule, a huge amount of energy (the speed of the molecule) is required. There is no mechanism for obtaining and transferring such an amount of energy to a water molecule (at natural water temperatures in the Earth's ecosystem).

However, it is known that the process of evaporation occurs constantly. So there is another mechanism. It seems that this mechanism is connected (or determined entirely) by the effect of the partial pressure of water vapor in the atmosphere. The amount of water vapor deficit determines the rate of evaporation and works according to the type of operation of the vacuum cleaner. It seems to me that this mechanism of evaporation is physically more real. The students and I considered various hydrometeorological conditions, which in principle agree with this thesis. What molecules (most or least "energetic") fly out (react) to this pulling mechanism, which are in the strongly structured skin-layer of water? And why does this skin layer of water always have a lower temperature relative to water in the volume: as a result of evaporation or as a result of energy radiation according to the Stefan-Boltzmann law? Or their combinations?

I am very grateful to you for starting a discussion about the evaporation process.

Sincerely, Nataliіa Kucherenko.

Howdy Natalіa Kucherenko,

Your comments are welcome. From them and your ResearchGate profile it is clear you are knowledgeable here. I agree that any topic in science may be treated better: that has been a regular occurrence in the history of science.

We have several topics here to address: an example of molecular unrest in evaporation which I used to enlarge awareness for the sound attenuation discussion; the concept of "latent heat" which seems to be misleading to me; the nature of evaporation from a water surface as molecular events; and your concept of atmospheric water vapor deficit as "drawing water" from the liquid.

My introduction to a more careful look at evaporation came from a question raised by a meteorologist colleague back in '82. He asked if evaporation was affected by atmospheric pressure, thinking that denser air might interfere with it. I checked into the topic and found that the Gibbs Free energy in the water was enhanced by the pressure on the surface, thus higher atmospheric pressure enhanced evaporation. Interesting, and in full accord with Dalton's discovery of partial pressures of the various gasses in moist air.

"Latent heat" as a convenient, if misleading, term was covered well enough in my earlier notes, but your question whether the classic view is valid, that more energetic molecules leave and thereby cool the surface, turns out to be quite interesting. On the one hand, when one reviews the distribution of molecular velocities in a fluid one finds very fast molecules in that tail of the distribution. That their momentum results from multi-molecule collisions is one explanation, but that they are fast enough to escape through the skin-layer of water is the case. While the surface tension of the skin-layer is strong enough to support a water spider with surface dimples that provide vertical tension support, a water spider foot is gigantic compared to molecular spacing. Further, when treating molecules as wave functions in Wave Mechanics, one finds that a molecule could actually "tunnel through" a barrier such as the hydrogen bonding of the surface to which you refer. The "free energy" of an individual molecule would be the measure to weigh against gravitation, which is a mild force by comparison. After all, molecular forces in a thread are strong enough to support a garment made of such threads against gravity. I find the classic view acceptable for molecules that leave a water surface.

On the other hand, your concept of water vapor deficit as a mechanism of "drawing" molecules from the liquid reminds one of the classic Greek philosophers' question whether the sun or the wind were more effective in "drawing water" from a puddle as it dried. Certainly evaporation is more rapid with a large water vapor deficit in the atmosphere, but in keeping with Borys original question herein whether correlation of sound attenuation with frequency were a "false correlation," one must ask whether the vapor deficit causes or enables evaporation, and how does nature perform the process? Remembering that evaporation is the net loss of molecules from the liquid which is also receiving water vapor molecules from the moist air, one must ask whether the latter is the more important effect of the vapor deficit. For myself, I am unable to see the "vacuum cleaner" analog as valid by comparison to condensation that accompanies evaporation in nature.

Your concept is imaginative, however, and my deepest experience in education, including the bastions of truth in science (for the moment), has been learning what was wrong with what I had been taught. A brick fell when dropped as surely in Aristotelian Physics as in General Relativity, but the latter is the preferred explanation (for now). There is much to know, keep thinking even if I am not convinced - you are the measure of value in your life.

Happy Trails, Len

P.S. This is great, but if we were to extend this discussion, perhaps you should start a fresh thread as a discussion or question to separate evaporation from the acoustics focus here. lfh

Dear Leonard Hall, I have to make some clarifications. Discussion "The distance of sound propagation in the ocean has a correlation with frequency. But sound in water has no dispersion. Maybe it's a false correlation?" I started, but the author of the idea (see the preprint REGULARITY OF THE WAVE ENERGY ABSORPTION PROCESS AS AN EXAMPLE OF THE PROPAGATION OF ACOUSTIC WAVES IN WATER) is Natalia Kucherenko.

Howdy Borys Kapochkin,

Thank you for that clarification. Actually, I had briefly checked the reference you cited and noted that you were listed as editor with others as authors. I had not made the connection with Natalia Kucherenko and her recent reply until now. I am pleased to have her view, and yours, but I am in debt to whoever authored and whoever communicated the idea because it triggered the line of thought and form of expression I discovered and expressed concerning acoustic wave propagation and attenuation in the ocean. Much of that thought was new to me as an application of familiar ideas - I hope it has been useful to others, however imperfect.

It has been written that researchers in the Renaissance were not smarter than in earlier eras but that better communication and mutual triggering of new insights for one another fueled a rapid increase in research results. Online communication nowadays is even better. Not all insights are valid, but all are valuable exploration. Oh, and we all know that "false correlation" only means it does not express a physical cause, statistically the variables are correlated so perhaps we could call it a "misleading correlation" instead.

Happy Trails, Len

Dear Colleagues. The discussion of the process of water evaporation aroused more interest in me than the topic of discussion about acoustics. I will allow myself to participate.

1. It turned out to be surprising to me that evaporation is not a simple trivial process. I never understood the physical principle of the spread of odors in the air. Now it feels like it's one and the same. Maybe I'm wrong.

2. You wrote that at high atmospheric pressure, evaporation increases. I want to draw attention to two contradictions.

A. According to the Boyle-Mariotte law, an increase in atmospheric pressure can occur only with a decrease in temperature (volume is a constant). On a climatic scale, evaporation should increase in winter. But in winter the water is cold and the number of fast molecules in the water drops sharply. This is a contradiction.

I have often observed that towels dry faster in cold dry air than in hot moist air. This is my personal experience and I believe it. But the number of fast molecules in cold water is less. This is a contradiction.

B). In accordance with Avogadro's law, a decrease in the concentration of water in the air (a decrease in the partial pressure of H2O) leads to an increase in atmospheric pressure (H2O is lighter than nitrogen and oxygen) and an increase in evaporation. This indirectly confirms Natalia's thesis.

3. Puddles, lakes, rivers and oceans form a cold surface film 3 mm thick. In 1 square meter of this layer, the number of water molecules is 10 to the power of 26. All these molecules are colder than water in volume by several degrees. Sometimes they are colder by 10 degrees Celsius. This layer was first discovered in 1940, when the sea was covered with ice at a water temperature of +4 degrees Celsius. The surface layer is colder, but its density is less (it does not sink). Here, water consists of associations of several molecules, and for this reason the number of single fast molecules is much less than in the volume. How fast molecules from the depths end up near the surface is hard for me to understand.

4. It's hard for me to imagine that fast molecules in the volume of water "know" about the partial pressure Н2О in the air. I don't understand how the water molecules in the air keep the fast molecules out of the water. Most likely they are forcibly pulled out into the atmosphere. Maybe I'm wrong.

5. I don't understand how the fast molecules in the water know that there is a strong wind over the water. Why, at the same water temperature, with wind in the air, the number of fast molecules in the water increases.

For me and, in general, for physics teachers at school, all this is very interesting.

Howdy Borys Kapochkin,

Great stuff, and of course this direction of the discussion is of interest to me also.

Firstly it is important to realize that molecular diffusion, wind, and turbulent diffusion in the wind are all involved whether it is the delivery of the scent of a flower or the distribution of water vapor in the air. Our agreement that science is simple is only true with understanding - it is not trivial, just clear.

Secondly, the water surface enables the pressure of the atmosphere to increase the Gibbs Free energy in the water, but that pressure is due to atmospheric circulations and synoptic pressure variations, as are the wind, sunshine, and turbulence over a water surface. The Boyle-Mariotte law and Avogadro's law are overwhelmed by the weather for an open water surface.

"I have often observed that towels dry faster in cold dry air than in hot moist air." Yes! the drying of the towels is due to net evaporation: condensation from the moist air, especially unto the evaporation-cooled towel, would reduce the net loss. Back home in Northern Minnesota it was standard procedure to freeze-dry one's wash in the winter. However, the vapor pressure over ice is only half the vapor pressure over water, thus freeze drying is delayed by that condition, but in a water droplet cloud, ice crystals thrive, grow large in the droplet humidity level and fall out of the cloud as snow.

Your point 3: You would enjoy reading in Kinetic Theory of Liquids by J. Frenkel to explore the answer and confirmation of your observations. He starts out with ice (called water rock by P. A. Shumskii in his Principles of Structural Glaciology) and the transition from ice to water turns out to be very complex. Ice is an amorphous solid as you may see in its capacity to flow as a glacier with pressure melting and refreezing allowing shape changes. Until it has been warmed to about 4 C (40 F) water includes clusters of molecules as ice fragments that explain its reduced density and appearance at the surface. Sea Ice with brine between relatively pure H2O crystals is even more fascinating. However, it is the distribution of molecular velocities that includes higher energy molecules, and it is these that leave from the surface rather than rising from the warmer water below the surface. And, of course, evaporation is less per unit area in cold water than in warm water.

Your point 4: molecules do not know anything except what to do next in the molecular unrest in a fluid, and they "know" that as collision behavior. This is true of both the water and the humid air. Water vapor molecules in the air that strike the water surface in their natural motion will tend to enter the fluid, while "fast enough" water molecules in the liquid will escape if moving toward the surface. It is very dynamic and the balance is net evaporation (or condensation in a different thermal environment). Think of the action of a pump on a shallow well with a piston that forces air from the space in the pipe above the water: the water is not pulled up into the pipe, it is pushed up into the pipe by atmospheric pressure on the well water surface, and then only until the downward force of the weight of the water column in the pipe equals that atmospheric pressure at about 10 meters or 33 feet - less at higher elevations. Similarly, no molecules are pulled in any direction during evaporation except at the water-skin where the nature of water molecules described by Natalia Kucherenko in her earlier contribution applies.

Your point 5: If you consider the humidity of the air in the surface layer over the water as supplemented by the evaporation process, then previously evaporated molecules become part of the return condensation flow. With a container over an area of the water surface isolating a volume, the air in the container will become saturated, that is no vapor deficit in the volume, or 100% humidity. Conversely, if a strong wind removed evaporated molecules from the air surface layer over the water the return flow would be reduced due to the lower vapor pressure of the passing air and net evaporation would be increased. The molecules are just doing their own thing in their environment and the net result follows.

Happy Trails, Len

Howdy Borys Kapochkin,

My wife told me about the joy/sorrow event of an earthquake close to home there. Nature is unaware of kindness ~Tao Te Ching. You may enjoy learning while you experience sorrow: survivors in centuries to come will benefit from what you learn by study of the current events that are tragic for today's casualties .

I had been concerned about the emphasis that developed in this thread on pressure that does enhance evaporation, since it is only a small effect, while "that lucky old sun" is far more important in supplying energy for the molecular unrest. When you again have time for evaporation it will be good to feel the energy in the molecular unrest without undue emphasis on pressure. Just a thought for future discussion.

Happy Trails, with sympathy for unhappy experiences, Len