Am I on the right track with this? Matter absorbs infra- red radiation (and heats up in the process) such that inter-molecular bonds are caused to bend and vibrate by the absorption of a photon. Molecular bonds are electrical in nature, and think of the bond as a spring; any stretching of those bonds would bring about both electrical and kinetic changes within the molecule.

Now, we are usually taught that there are three forms of heat transfer: conduction, convection and radiation. Conduction and convection are regarded as kinetic phenomena in which heating increases the motion of atoms in a solid or fluid, while radiation accounts for heat transfer in a vacuum.

Has anyone ever proposed that conduction and convection can be regarded as instances of radiation, modelling the greater motion of atoms in solids and fluids in terms of the kinetic effects of light emission and absorption among these atoms' electrons?

Since all heat is supposed to be accompanied by the emission of light, it would be interesting if all heat phenomena could be regarded as basically electromagnetic -- although there is probably no real theoretical or practical progress to be made by investigating such a notion!

Well, if you consider that structure of an a molecule is electronic. Molecules and atoms interact through forces. They dont really touch. There has to be some way to mediate the interaction. Could be that in kinetic interactions we really dont seen the photons because they are too "fast" at close distances for us to detect. It would be more consistant.

I think matter can absorb other parts of the EM spectrum and 'heat up' as well - eg, the surface of the Earth absorbs UV, and then re-radiates it to the atmosphere as IR; it is the property of 'greenhouse gases' (which are transparent to UV) to absorb and reflect IR that leads to lower atmospheric warming. We sense IR as heat.

conduction, convection and radiation are the three basic forms and are linked to the medium of transfer - solid, fluid, and vaccuum (though for radiation, that's a bit misleading because radiation can penetrate fluids and solids; it's more a difference between whether or not the transfer of energy is independent or dependent upon the medium)... but there are also some further catagories which identify energy transfer between different media (eg, between a fluid and a solid)...if you want some names and definitions, let me know...
Can't say for certain, but I believe that is how it's viewed at the sub molecular level (and the quantum level for all I know :huh: ) ... or...all electromagnetic phenomena could be regarded as 'kinetic'?
:unsure:

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That would be good too, Cran. I mean, Light can be viewed as photon's having K.E. . However, what do we do about the Potential energies? I mean, can we say that the P.E. of the moon due to the earth is Kinetic energy, or EM energy?

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Ah, now we're getting into physics... :blink:

rahuldandekar, what I know about physics is.... I have a nice picture of Einstein next to my computer monitor ...

I think the concept of potential energy is related to kinetics - it describes the object's potential to express kinetic energy - in natural mesoscopic and macroscopic systems, it is most often applied to relative position and gravitational potential energy - the moon is falling around a centre of gravity that it shares with the Earth, and both are falling around a centre of gravity they share with the sun ... if something were to get in the moon's way (eg a meteor) it would experience the expression of the moon gravitational potential energy as kinetic energy ... plus its own potential energy as kinetic energy ... and so would the moon - result? a shattered meteor, a hole on the moon, and the release of x amount of energy, including electromagnetic radiation (some rather excited photons - it's party time!) ... is EM radiation an expression of kinetic energy? why not? If it can do 'work' - ie, apply force - it must be kinetic by definition...

but physics... that's like maths ... pi, rho, sigma, tau, phi, chi, omega ... I don't know - it's all Greek to me :blink:

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You seem to forget that you can heat a gas simply by compressing it. The heating here is purely due to the mechanical work being done by compressing the gas and there is no radiation involved at all.

When a gas is heated by radiation, there are basically two processes possible: 1) molecules are dissociated by UV radiation with the fragments carrying away the excess energy of the UV radiation as kinetic energy and hence heating the ambient gas; 2) IR radiation leading to molecular vibrations and rotations which, through inelastic collisions, can transfer translational kinetic energy to other molecules or atoms and hence heating the gas in this way.

By the way, what I was always wondering is if what we subjectively perceive as 'heat' is actually the kinetic energy of the molecules hitting our skin or the infrared radiation associated with it. This might be an interesting question to pursue in this context.

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Hi Thomas,

What we perceive subjectively as 'heat' is the increase in molecular excitation in the cells of our skin and nerve receptors, no matter how the energy is transferred to those cells ... and it is 'relative' - fill three large bowls or buckets with water (1 with hot, 1 with cold, and 1 with warm or tepid), then put one hand in the hot water and the other hand in the cold water for about 30 seconds - then put both hands in the tepid water... and it will feel 'hot' and 'cold' at the same time!

And heating gas by compression still produces IR photonic discharges due to the increased number of impacts between the molecules... that's where the 'heat' comes from.

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But then you should also have some kind of 'heat' sensation if you increase the energy transfer to the skin by increasing the density of the gas rather than the temperature ( the total energy transfer should be proportional to the product of both). On the other hand, the infrared radiation is unlikely to increase by much in this case as an increase of density also means an increase of IR absorption.

Your argument that a compression of a gas also produces IR radiation is correct if you have a molecular gas. However for an atomic gas there will not be any significant amount of IR radiation being produced because the kinetic energy gained in the course of the compression is much too small to excite atomic energy levels from the ground state.

The relativity in the subjective 'heat' sensation is obviously merely due to the 'conditioning' of the corresponding regions in the brain. If you just wait long enough, the temperature of the tepid water will feel the same for both hands.

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Yes
:huh: Don't follow you, there ... IR absorption by what? :huh:
:huh: Suggests there won't be much increase in temperature then...
<_< No, the relativity is due to relative differences (thermal gradients) because we sense heat and cold as relative not absolute values and it has nothing to do with conditioning any areas of the brain ... likewise, if you stood naked out in the snow for long enough, you would not feel cold... you would look blue, but you would not feel cold h34r:

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I would question this. The nerve cells for detecting heat do actually not reach into the outer layer of the skin and I can not imagine that molecules hitting the skin will produce any noticeable increase of the temperature (again, if they would, the heat sensation would be related to the air pressure rather than the temperature).

Absorption by the molecules. Any IR radiation emitted by a molecule can again be absorbed by another molecule and turned into mechanical energy again. If you increase the molecular density, you will have a corresponding increase in IR radiation produced in a given volume element, but this radiation will also be absorbed again more easily. Consequently, the amount of IR radiation reaching the skin should be pretty much independent of the molecular density.

The kinetic energy (i.e. the temperature) of the atoms will increase through the compression, but this will not be associated with any IR emission (unlike for a molecular gas).

I do not see how the nerve cells should be able to detect a thermal gradient. All they detect is the 'heat energy' that reaches them. The processing of this information is completely done by the brain, i.e. it is the latter which is responsible for the relativity of the heat sensation.

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Okay... and your references (author date title) for each point are....? <_<
I only ask, because they don't jibe with my (admittedly vague) memories of what I thought I'd learned :huh:

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Why do you need references here? It is just the logical application of some basic physics principles (for your information, I am a physicist by profession, so I can formulate my own insights if required and don't need to merely quote other sources).

Well, sometimes you just have to forget what you 'learned'. The point is that the official school and university curriculum contains many simplifications, half-truths and flawed views which prove inadequate when it comes to treating particular problems. I had to revise also many of the views I had been taught when I examined some topics more thoroughly.

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I'm sorry, Thomas, but I am not a physicist by profession, and therefore I am not in a position to compare your 'insights' with the 'simplifications, half-truths and flawed views which prove inadequate when it comes to treating particular problems' being marketed by 'the official school and university curriculum'... and whilst I am fully prepared to 'unlearn' anything (and have done, many times, after being convinced that it is wiser to do so... most often in, and by, the same 'official school and university curriculum'), I see no reason to do so based purely upon one person's 'insights'; physicist or otherwise... no offense intended.

As a professional physicist, you will understand both the requirement and the rationale.

I need to understand the principles you are applying, and why... I am a mere student, caught in the 'official etc', and a very poor physics student at that...

I ask that I may learn...

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