A science question

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Microwave radiation represents a good compromise of energy, transmission and absorption that makes it very useful for cooking. Like IR it is absorbed by matter (not all matter - microwaves pass through plastic and paper with little effect, but not water and many types of glass which absorb them readily), but unlike IR it also passes through much of matter. The additional energy of microwaves enables a fair percentage of them to penetrate to the interior of food and heat it faster.

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I could be wrong, but I think microwaves and IR heat objects through different mechanisms. IR is directly absorbed and transfered into kinetic energy. Microwaves cause polar molecules to flip in synch with the EM waves causing friction between molecules which is then transfered into kinetic energy. This is why paper does not heat up but water, because it is polar, does heat up. Does this qualify as separate mechanisms, or am I smoking out of the wrong pipe again?

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Taking the simple case of an atom moving at a constant velocity in a vacuum, why isn't its velocity a measure of its heat? Why wouldn't increased velocity be interpreted as increased heat.

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Increased velocity is increased kinetic energy. Temperature is the average kinetic energy of a body. For temperature or the transfer of heat you need at least two atoms. I would expect that without two atoms you would not be able to measure the "heat" content of a single atom. Kind of a Maxwell's Demon sort of exercise.ABE:
Sylas snuck this tidbit in as well. We seem to agree at some level:"Heat seems to be a macro-level phenomenon; really only defined in terms of large systems; not individual molecules or individual photons."This message has been edited by Loudmouth, 03-07-2005 15:20 AM

Implication under debate: "Light is not heat; except when it's part of the radiative transfer of energy from hot objects to cold ones."

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Following the implications of this, say we have a hot object and a cold object, both emitting EMR with a profile appropriate to temperature. Some proportion of this EMR from each strikes the other and is absorbed, but only the EMR from the hotter to the colder object is heat, according to your definition. This means the EMR from the colder to the hotter is...what? You've said it isn't heat, but then what is it? This seems contradictory.
  —Percy

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I think the implication is wrong as well. I do agree that light is photons which have the capability of heating an object. However, light itself is not heat. In your example the colder object is still heating the hotter object through EMR, just at a slower rate than the hotter object's heat loss, in keeping with the Laws of Thermo. If heat transfer is through EMR I think Sylas was incorrect when he stated "from hot objects to cold ones". If he removes that part of the statement I think he is correct.This message has been edited by Loudmouth, 03-07-2005 16:08 AM