A science question

Percy,I agree that heat can be transferred by conduction and convection as well as by radiation (I mean the act of radiating, in this case). However, Holmes appears to think (and no one except me appears to correct his thought) that there are different kinds of heat, only one of which is infrared light. In fact, unless I am mistaken, ALL heat is infrared radiation (invisible light with long wave lengths).Holmes IS correct in that heat can move around within the earth system via conduction or convection as well as radiation (the act of radiating) but that the ONLY way it can be lost to space is via radiation (the act of radiating). However, he is INCORRECT if he thinks there are two or three different forms of heat energy. Either that or *I* am wrong in asserting that ALL heat is light, a point about which I would readily accept correction--myself not being an expert in the science of heat or light.--TheLit

I think Percy's point is that you are mistaken; all heat is the kinetic energy of atoms. Sometimes this energy is transmitted via IR radiation; other times it is transmitted via the direct collision of atoms.

I think that calling IR radiation "heat" is sort of incorrect.Heat is a measure of the velocity of the molecules of a material. It is a form of energy. If that is a definition of heat then IR radiation is not heat. If heat is energy in the electromagnetic spectrum then I don't see why radio and gama radiation isn't "heat" too.We call a lamp that radiates in the IR (or mostly in the IR) a "heat" lamp because that is how we sense it. The IR radiation transfers energy to our skin which produces a sensation of heat.My conclusion would be that IR radiation is not "heat" but then I think we might be using heat in too careless and colloquial a way.

You are mistaken, in fact. A body gives off radiation depending on its temperature. The hotter the object, the more its emitted radiation shifts from infrared into higher frequencies. A sufficiently hot object will radiate primarily in the ultraviolet.Electromagnetic radiation includes radiowaves, visible light, hard gamma radiation, and everything in between and also beyond. "Infrared" radiation is just light at a longer wavelength than what we can see directly.We tend to associate infrared radiation with heat because warm objects in our normal experience are radiating at that wavelength.I can't makes sense of "all heat is light". No one wavelength of light stands out as have any special association with heat in general. Light is just a form of energy.Cheers -- Sylas

I agree with the various replies already posted. The key points:

1. Heat is the motion of atoms and molecules.
   ​
2. Heat can be transmitted between atoms and molecules by contact. For example, a fast moving gas molecule colliding with a slow one will impart some of its kinetic energy, its heat, to the slower one. The slower one is now hotter, the hotter one is now cooler.
   ​
3. Heat can also be transmitted by electromagnetic radiation, but EMR is not heat, it is energy. As Sylas says, matter at temperatures we're comfortable with emits EMR in the infrared region. When a molecule in the heating element of a heat lamp becomes hot enough it gives off a photon of energy at a frequency in the infrared region and temporarily becomes cooler (the electricity passing through the element quickly heats it again). This photon strikes a molecule of your skin and gives up its energy to that molecule, which now vibrates faster, and you experience this as heat.
   ​
4. For completeness, and to avoid sending JonF into another coughing fit, heat can also be transmitted by convection, but this is not a transmission of heat between atoms and molecules, but merely the motion of atoms and molecules containing heat that are part of a viscous system and are moving because they are at a different temperature from other parts of the viscous system. Naturally, in a convecting system heat is also exchanged between atoms and molecules by collisions and EMR. (I suppose ancient catapults sending flaming tarballs over castle walls is another form of heat transmission. We could call this ballistic heat transmission. )

But we're getting off the subject. My original point, which is the same point others have also made, is that we can't measure all the contributions and losses of earth's heat to perform an accurate heat budget. But we *do* know that the earth is losing heat to space and not the other way around because the earth is hottest on the inside. If we were gaining heat from space we would be hottest on the outside. And we *do* know that the interior of the earth is hotter than the outside by direct measurements down a few miles, and by seismic studies revealing a molton interior.--Percy

Okay guys,I am actually confused, now. I thought all heat was IR (which I thought was part of the light spectrum).From this online dictionary heat is defined as: While this seems to be what Percy said (in much abbreviated format), this definition doesn't UNCONFUSE me at all. I would think that IF heat can be "transmitted...through empty space by radiation," then heat is, in fact, radiation (light)--regardless of whether it can be transmitted other ways or what different radiation wavelengths occur as the temperature (amount of heat?) increases.I likely have some fundamental misunderstanding of "heat." My last technical dealings with "heat" was in level I physics, in which case it was usually regarded as energy lost from a system due to friction.--TheLitThis message has been edited by TheLiteralist, 03-07-2005 00:15 AM

Percy,Are you saying that kinetic energy IS heat energy? I thought heat was merely a by product of kinetic energy.

Hi Sylas,I'm still convinced that IR is heat (I will readily concede if I can be made to understand...this ISN'T about theology after all). But the IR must continue to be radiated, also, I think--or else there would be no heat radiated from the object, right? I think that both temperature and the wavelengths emitted depend on the amount of kinetic energy present in the system; however, only the IR radiated is the heat of the object. (I could be wrong, I readily admit). This link seems to disagree with you guys (or I'm reading it wrong...entirely possible). While I agree that ALL wavelengths are energy...it appears to me that only (far) infrared wavelengths are HEAT energy (which I have always understood to be a type of energy all its own and different from, say, potential, kinetic, mechanical, or chemical energy). Apparently not even all of the infrared spectrum is considered to be "heat." Heat is also "just a form of energy." If all heat is actually IR, then all heat is light; however, not all light would be heat, if that makes sense. Now, if there are different kinds of heat (I don't believe this, yet), then not all heat is light...but no one has yet demonstrated that all heat isn't IR.I really don't think that kinetic energy (of molecules) IS heat; rather, molecular kinetic energy GENERATES heat (IR). I may be wrong, but if the amount of molecular kinetic energy increases (for whatever reason), IR will increase in amount radiated (temperature increases) and also the molecules will begin radiating in other wavelengths (including visible and beyond). However, the IR must continue to be generated or else there would be no heat felt from the object in question (the sun, for example, generates nearly the complete, if not the complete, light spectrum--including IR--and it VERY hot).Feel free to point out my ignorance...I'm truly curious why several very knowledgeable people are disagreeing with me...I can only surmise that I misunderstand the concept of "heat" fundamentally, in some way.--TheLit

CF,I could be wrong, but I am not convinced, yet. Right now, I see it this way:

• Kinetic energy is NOT heat energy; however, kinetic energy produces heat energy, and the heat energy of a system is always directly proportional to the kinetic energy of the same system
• Kinetic energy (and, indirectly, heat energy) can be transferred to another object by physical contact (i.e., by molecular collisions). If this transferrance of kinetic energy occurs, then the kinetic energy and, therefore, the heat energy of the contacted object will increase (while the kinetic energy and heat of the first object decrease).
• If radiated heat energy (IR light) contacts another object, it indirectly increases the heat energy by increasing the kinetic energy of the irradiated object

Either I'm wrong or you guys are confusing kinetic energy with heat energy. Since the heat energy of a system is directly dependant upon kinetic energy of the system, this would be completely understandable. The two forms of energy, while extremely interrelated and interdependant, are completely different forms of energy...I thought. Temperature is a measurement of kinetic energy only because heat energy is always generated by kinetic energy (and always in dependable proportion to the kinetic energy).OTOH, several knowledgeable people are agreeing with you and finding my assertions problematic; for this reason only, I permit a shadow of doubt in my mind about my position on this matter. It's just that, so far, I haven't seen anything to change my mind.--TheLitThis message has been edited by TheLiteralist, 03-07-2005 00:13 AM

This statement is simply wrong. The reason you don't feel them as "heat" are two fold (I believe). One is that the intensity of the remote control is very very low. If it put out the several 10's of watts that a bathroom "heat" lamp put out you would feel it so some degree. Also the different wave lengths of EM radiation react differently with your skin. Some are poor at transmitting the energy they carry and so will not be experienced as much as heat (or not at all). Gamma radiation will, in a lot of lower intensites not be experienced at all as most will pass through you. Some radio waves will definitly be experienced as heat. There was a suggestion that by using the right wavelengths it would be possible to heat a home by making each room into a large microwave. As long as they didn't penetrate too deeply they could warm you without warming the air and so be very efficient. I think they would have a major PR problem though (however good the science behind it) .So a wide range of different wavelengths will allow an energy transfer. That will raise the kenetic energy of the skin and be experienced as heat. Some wavelengths will be inefficient some not.There is no "heat" energy. Heat is a manifestation of the kenetic energy of the atoms of materials. It is colloquially called "heat energy" for that reason.

Hi JonF, Well, I was hoping that my constant "L" (the rate at which the earth loses energy to space) would make knowing the complex movements of heat energy within the earth unnecessary.I wonder if understanding the complexities of heat movement within the earth system is necessary for estimating the current energy contained by the earth system or the rate at which the earth generates energy. I was hoping not and thought that a mean earth temperature plus some calculations based on the rotational/revolving motions of the earth might do the trick.Oh well...whether it can be done or not...I certainly can't do it! So, it's pointless anyways, I guess.--TheLit

Your link is a rather simplified non-technical description, but it is quite correct. It says that

quote:

---

Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat. The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared.

---

In other words, in our experience, the things we consider to be "warm" are emitting in the far infrared; and more particularly our bodies are adapted to detect heat at these kinds of temperatures.The peak wavelength in centimeters of heat radiation times the temperature in degrees Kelvin of the emitting blackbody is a constant 0.2898. This is Wien's Law. A warm kitten is around 310 Kelvin. A fire is around 600 Kelvin. The peak wavelengths for these warm things is thus 10^-3 to 5*10^-4 centimeters, which is infrared.As something gets hotter, it starts to glow. This just means that the emitted heat is starting to include visible light. But long before this point we are reaching temperatures which are too hot for us to have any useful sensory detection. Things that hot burn instantly, and no special heat sense is required. Our finer senses are tuned to work well with cooler temperatures.Visible light is around 5*10^-5 centimeters. A blackbody at 6000 degrees will peak at around this temperature; and that is indeed the temperature of the Sun. So the Sun's heat radiation is actually visible light. We see this with our eyes, but it does not appear to us as heat, even though it is. The heat we feel on a warm day is (I think?) mostly the indirect infrared radiation from our environment which has been heated up by the Sun.Added in edit: Put another way; our vision system has adapted to work well with solar radiation; and our heat sense has adapted to be most sensitive to the range of temperatures in our local environment on Earth.If you get something even hotter, like around 60,000 degrees, it will radiate heat in the ultraviolet.Cheers -- SylasThis message has been edited by Sylas, 03-07-2005 01:59 AM

NosyNed, Okay. I guess that could be batted around for a bit. To prevent that, I will concede (not only due to your post but also due to Sylas's post)--for now, for argument's sake--that no particular light wavelength can be classified as heat.This actually would make the discussion clearer perhaps (for me, anyways)...thanks.
--TheLit

As a pretty good rule of thumb: always go with Sylas's posts. If they are different from mine 99/100 it is mine that is wrong.This message has been edited by NosyNed, 03-07-2005 02:35 AM

Ha ha.Well, you two are agreeing this time--for what it's worth.