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Author Topic:   A science question
TheLiteralist
Inactive Member


Message 61 of 148 (190408)
03-07-2005 3:05 AM


Kinetic Energy vs. Light Energy
Everybody,
Due to the most recent posts by Ned and Sylas, I concede (for argument’s sake) that the wavelength is irrelevant to defining heat.
The problem then becomes even simpler.
Heat is light--always. All the laws that apply to light apply to heat. Heat can be radiated, reflected, refracted, or absorbed. Therefore, heat, regardless of it’s source, is a candidate for being lost to space via radiation.
Kinetic energy produces light--always. Usually this light is invisible and is felt as heat.
Heat (or light) is NOT kinetic energy, but heat is very, very closely related to kinetic energy. Kinetic energy produces heat. Heat produces kinetic energy.
I think (emphasize: THINK) it is only an illusion that heat is conducted. I believe the kinetic energy is conducted, and the heat results from the increased kinetic energy. Similarly, irradiation increases the kinetic energy--not the light energy--of the absorbing system. However, increased heat results from the increased kinetic energy.
(Am I arguing apples and oranges? I feel like I'm making much ado about nothing, in a way--OTOH, it seems fundamental to the discussion--plus I'm having fun blathering on about it, I suppose.)
--TheLit

Replies to this message:
 Message 64 by Sylas, posted 03-07-2005 4:45 AM TheLiteralist has replied
 Message 79 by crashfrog, posted 03-07-2005 12:41 PM TheLiteralist has replied

  
TheLiteralist
Inactive Member


Message 62 of 148 (190411)
03-07-2005 3:10 AM
Reply to: Message 57 by Sylas
03-07-2005 1:09 AM


IR from the Sun?
Sylas,
Just in case you're curious...
From this link:
More than half the Sun's power output is in the form of infrared light, though much of it is absorbed by the Earth's atmosphere.
Of course, being absorbed by the earth's atmosphere is still being absorbed by the earth system (it's mighty convenient for us, too, I imagine...I'm only too happy to have a bit of the IR for myself, but I am just as happy to let the atmosphere have the rest...I believe in sharing!).
--TheLit

This message is a reply to:
 Message 57 by Sylas, posted 03-07-2005 1:09 AM Sylas has replied

Replies to this message:
 Message 63 by Sylas, posted 03-07-2005 4:26 AM TheLiteralist has not replied
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Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 63 of 148 (190420)
03-07-2005 4:26 AM
Reply to: Message 62 by TheLiteralist
03-07-2005 3:10 AM


Re: IR from the Sun?
Your link correct, but it is not in conflict with the information people have been trying to explain to you. You need to understand that a light source has a spectrum, with a range of frequencies, and this spectrum depends on (amongst other things) temperature. There is no one frequency which means "heat". This is the first and most important think people are explaining to you.
I have said that the Sun (being much hotter than most things in our normal experience) radiates at shorter wavelengths, with a peak at the visible wavelengths. Your link says that most of the power output of the Sun is infrared. How can both these things be true?
The solar spectrum is quite close to a blackbody spectrum, with a temperature of about 5800 degrees Kelvin and a peak in the power spectrum at a wavelength of around 500 nm. Blackbody is a very important kind of spectrum; you can find a lot about it on the web. Here is a picture of the power spectrum for three stars. One is cooler than the Sun and one is hotter. Discussion available at The Solar Spectrum (University of Tennessee).
Notice how in each case, the spectrum rises rapidly to the peak, and then tails off into the longer wavelengths. Some light is at a longer wavelength than the peak, and some is at a shorter wavelength. The shape of a blackbody spectrum means than more power is emitted at wavelengths longer than the peak than at wavelengths less than the peak.
Now as has been explained, the Sun has the peak in the visible spectrum, and so the long tail of the spectrum goes off into infrared. This means that the peak is visible light, but there is more power at longer wavelengths than at shorter wavelengths, which is what your link is saying.
Your link provides an image of the Sun at 1083 nm, which is about 10000 Angstroms. This is only one infrared wavelength; not the whole spectrum; and it is about twice the wavelength of visible light. It is, in fact, just a little longer than the peak wavelength the cooler star Antares. It is a peak for a body at about 2400 Kelvin; half the Sun’s temperature.
This is still significantly less infrared than the far infrared which the link you gave a few posts ago singled out as thermal radiation. What we normally think of as thermal has a wavelength more like 5000 nm. So ANY light can be heat radiation.
Now if we apply Planck’s equation (ref Blackbody Radiation at Rutgers University) to the wavelength of 1083 nm, and using the solar temperature of 5800 Kelvin, we get a power magnitude Bλ of 9*1012. But the peak wavelength is about 500 nm (which is visible yellow) and this has a power magnitude of 2.7*1013; which is three times greater.
Sure; most of the power is infrared. But it is spread out over a large range of the spectrum. For good vision focus, you want to single out a small part of the spectrum, and to get the most power in a small range you should go to the peak.
All of this is simply to explain why your link is correct, and why this does not conflict with the other information people have been explaining. And as an object gets hotter than the Sun, you soon get to a point where most power output is ultraviolet, with a peak in the far ultraviolet. Have a look at the spectrum for the hot star Spica. The radiates nearly all its heat in the ultraviolet.
Cheers -- Sylas

This message is a reply to:
 Message 62 by TheLiteralist, posted 03-07-2005 3:10 AM TheLiteralist has not replied

  
Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 64 of 148 (190422)
03-07-2005 4:45 AM
Reply to: Message 61 by TheLiteralist
03-07-2005 3:05 AM


Re: Kinetic Energy vs. Light Energy
Heat is light--always. All the laws that apply to light apply to heat. Heat can be radiated, reflected, refracted, or absorbed. Therefore, heat, regardless of it’s source, is a candidate for being lost to space via radiation.
Kinetic energy produces light--always. Usually this light is invisible and is felt as heat.
Heat (or light) is NOT kinetic energy, but heat is very, very closely related to kinetic energy. Kinetic energy produces heat. Heat produces kinetic energy.
That’s not bad! It is closer to being correct than the definition of heat as kinetic energy; at least by modern usage.
From heat at hyperphysics;
quote:
Heat may be defined as energy in transit from a high temperature object to a lower temperature object. An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy. The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object - this is properly called heating.
Thus heat is energy in transit; not the kinetic energy itself. The one quibble I have with your description is where you say heat is always light; there are other ways in which energy flows from hot objects to cooler ones, and they are heat as well.
Your conclusion: "Kinetic energy produces heat. Heat produces kinetic energy." seems pretty good to me at capturing the distinction between heat and kinetic energy of molecules.
Cheers -- Sylas

This message is a reply to:
 Message 61 by TheLiteralist, posted 03-07-2005 3:05 AM TheLiteralist has replied

Replies to this message:
 Message 66 by Silent H, posted 03-07-2005 5:19 AM Sylas has not replied
 Message 67 by TheLiteralist, posted 03-07-2005 5:25 AM Sylas has not replied
 Message 73 by Percy, posted 03-07-2005 9:57 AM Sylas has not replied

  
Silent H
Member (Idle past 5819 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 65 of 148 (190423)
03-07-2005 5:10 AM
Reply to: Message 62 by TheLiteralist
03-07-2005 3:10 AM


Re: IR from the Sun?
Sorry that my being in a different time zone kept me out of the loop on this one. Sylas, Percy, and Ned have all done a pretty good job explaining this, yet you seem to be having an a priori hangup regarding what heat is, and so it leads to confusion.
Let me have a stab at this...
I think you are confusing heat with energy. From merriam webster, energy is:
3 : the capacity for doing work
4 : usable power (as heat or electricity); also : the resources for producing such power
One kind of energy is based on physical motion (momentum energy) of particles and so transmitted directly from one system to another based on conduction (or convection I suppose though that seems only like a forced/extended conductive situation). This is kinetic energy.
Another kind of energy is electromagnetic. It has the ability to induce changes in systems over a distance without direct physical contact between particles.
In a system containing energy (general) a particle may give it off via kinetics or electromagnetism. That is it can start moving around more as a whole, or its electrons can start moving about more giving off electromagnetic radiation (there are a bit more but this is simplified).
Heat is an arbitrary concept (kind of like weight) used to measure the amount of kinetic energy contained in a system. Thus heat can be thought of as a form of energy.
However, it is true that as energy increases in a system one will have increases in both kinetic and electromagnetic manifestations of that energy. Thus heat can be determined indirectly from EM radiation (they vary proportionally). That is after all why IR goggles will help pick out a hot body from colder surroundings.
Thus you cannot say heat is light, but rather that light is energy and to some proportional degree an indicator of kinetic energy and so heat in a system.
Light is not a loss of heat, but of energy, though certainly a loss of energy means that the system will lose kinetic energy as well.
My original post is still okay, though obviously not well stated. Loss of energy will be through kinetics and EM. Since there is a vacuum and a vacuum is an insulator, kinetic energy (and so "heat") will not be lost, except as molecules actually leave the atmosphere altogether (as did happen deep in earth's past). There is no sense of earth's environment actually "cooling" (transferring heat through kinetic mechanisms) into space.
It is true that as energy is drained via EM, kinetic energy which is not escaping can be transferred to EM and so lost that way.
I hope this seems clearer.

holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)
"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

This message is a reply to:
 Message 62 by TheLiteralist, posted 03-07-2005 3:10 AM TheLiteralist has not replied

  
Silent H
Member (Idle past 5819 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 66 of 148 (190424)
03-07-2005 5:19 AM
Reply to: Message 64 by Sylas
03-07-2005 4:45 AM


Re: Kinetic Energy vs. Light Energy
It is closer to being correct than the definition of heat as kinetic energy
I'm not sure I agree. I mean I do agree that it is better to say heat is very closely related to kinetic energy, rather than is kinetic energy, but I have a hard time with his assessment that heat is light and kinetic energy produces light.
Let's take a hydrogen system with no electrons. If energy is transferred to it, will it radiate EM energy? How? Maybe I am missing something, but it seems that in that case it will only be able to express itself via kinetic energy and "heat transfers" and not in the form of light, except if one reaches an energy level where hydrogen fuses or other particles can form via hydrogen collisions.
I look forward to being corrected and so enlightened.

holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)
"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

This message is a reply to:
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TheLiteralist
Inactive Member


Message 67 of 148 (190425)
03-07-2005 5:25 AM
Reply to: Message 64 by Sylas
03-07-2005 4:45 AM


Re: Kinetic Energy vs. Light Energy
Sylas,
Thanks for the link. Thanks for the replies, too.
The one quibble I have with your description is where you say heat is always light; there are other ways in which energy flows from hot objects to cooler ones, and they are heat as well.
Uh oh. Maybe I'm completely wrong, then. What are the other ways in which energy flows from hot objects to cooler ones? If it's conduction and convection, I'm dead wrong!
See, I've been considering heat transfer via conduction to be a sort of illusion. What I mean is that there is actually a transfer of kinetic energy (molecular collisions). This transfer of kinetic energy results in increased heat, of course, which I considered to ALWAYS be light.
Oh well...,
--TheLit

This message is a reply to:
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Replies to this message:
 Message 69 by Silent H, posted 03-07-2005 5:31 AM TheLiteralist has replied

  
Silent H
Member (Idle past 5819 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 68 of 148 (190426)
03-07-2005 5:29 AM
Reply to: Message 50 by Percy
03-06-2005 10:30 PM


Re: IR and EM
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.
I do not know if this is true at all. Just because the interior of the earth is hotter, is no indication that the exterior is losing heat. It may be that the energy being generated internally is greater than that being absorbed by the external surface.
Think of a pot of baked beans. One can keep the fire going beneath and have a heat lamp going on the top to match any potential cooling to the outside atmosphere (or perhaps simply put on a lid). Eventually a thick dense layer (skin) may form at the top. The skin will feel warm (perhaps hot) but much cooler than the churning mass below, which from time to time will explode through the surface violently.
It is true that a lot of energy has been put into our earth's system, but over time we have lost layers of atmosphere and energy has become stored in new ways (life).
I am uncertain if we can definitively say we are losing more heat than gaining, from the sun.

holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)
"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

This message is a reply to:
 Message 50 by Percy, posted 03-06-2005 10:30 PM Percy has not replied

  
Silent H
Member (Idle past 5819 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 69 of 148 (190427)
03-07-2005 5:31 AM
Reply to: Message 67 by TheLiteralist
03-07-2005 5:25 AM


Re: Kinetic Energy vs. Light Energy
What are the other ways in which energy flows from hot objects to cooler ones? If it's conduction and convection, I'm dead wrong!.. See, I've been considering heat transfer via conduction to be a sort of illusion... This transfer of kinetic energy results in increased heat, of course, which I considered to ALWAYS be light.
You are wrong. See my post #65 and hopefully it will seem clearer.

holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)
"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

This message is a reply to:
 Message 67 by TheLiteralist, posted 03-07-2005 5:25 AM TheLiteralist has replied

Replies to this message:
 Message 70 by TheLiteralist, posted 03-07-2005 5:43 AM Silent H has replied

  
TheLiteralist
Inactive Member


Message 70 of 148 (190428)
03-07-2005 5:43 AM
Reply to: Message 69 by Silent H
03-07-2005 5:31 AM


Re: Kinetic Energy vs. Light Energy
Holmes,
You are wrong. See my post #65 and hopefully it will seem clearer.
If I have understood Sylas correctly, then ALL light is heat, but not all heat is light. If this is the case, then we are BOTH wrong, right? I say this because you seem to separate heat utterly from light and kinetic energy per phrases like...
However, it is true that as energy increases in a system one will have increases in both kinetic and electromagnetic manifestations of that energy. Thus heat can be determined indirectly from EM radiation (they vary proportionally). That is after all why IR goggles will help pick out a hot body from colder surroundings.
...
Light is not a loss of heat
Perhaps we will both be enlightened? But just think of how much more typing than you I had to do in order to be enlightened! I can be awfully stubborn, sometimes.
--TheLit

This message is a reply to:
 Message 69 by Silent H, posted 03-07-2005 5:31 AM Silent H has replied

Replies to this message:
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Silent H
Member (Idle past 5819 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 71 of 148 (190435)
03-07-2005 7:25 AM
Reply to: Message 70 by TheLiteralist
03-07-2005 5:43 AM


Re: Kinetic Energy vs. Light Energy
ALL light is heat, but not all heat is light. If this is the case, then we are BOTH wrong, right?
All light is not heat and certainly not all heat is light. I did some more perusing and found that most of what I said is dead on. I may have to revise my own conception of heat to include more EM effects, but that is more of a semantic shift than a purely conceptual one.
Here is a good link on this subject, specifically regarding concepts of temperature which is generally what people think of as a measure of "heat".
But even better, and more concise, is Wikipedia's entry on Heat. It backs up almost everything I have been saying. Here we go...
what it is...
Heat... is the transfer of thermal energy between two bodies which are at different temperatures... The relationship between heat and energy is similar to that between work and energy. Heat flows between regions that are not in thermal equilibrium; in particular, it flows from areas of high temperature to areas of low temperature. All objects (matter) have a certain amount of internal energy that is related to the random motion of their atoms or molecules. This internal energy is directly proportional to the temperature of the object. When two bodies of different temperature come into thermal contact, they will exchange internal energy until the temperature is equalized. The amount of energy transferred is the amount of heat exchanged.
how it is transferred (note convection is form of conduction)...
heat tends to move from a high temperature region to a low temperature region. This heat transfer may occur by the mechanisms conduction, and radiation. The term convection is used to describe the combined effects of conduction and fluid flow. In the past, this has been regarded as a third mechanism of heat transfer, but, logically, it is not a mechanism of its own.
Conduction related to kinetic energy...
Conduction is the most common means of heat transfer in a solid. On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms.
EM radiation (note I am wrong in that it appears anything other than a bare neutron is capable of EM output, though my guess is that this is less relevant than the activity of electrons in producing EM "light")...
Radiation is a means of heat transfer. Radiative heat transfer is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.
Regarding EM as heat...
Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF hair removal.
Unlike kinetic energy which does transfer heat when two systems are put into contact, EM radiation is not the same. For radiation to be a source of heat it must be absorbed (which is reliant on the target body). EM radiation may go unabsorbed and can even be reflected, thus no heat involved.
However for the purposes of this discussion it would seem IR radiation is a form of heating, though to my view (biased from a chemical-kinetic education) it is more accurately described as energy loss than heat loss.
Hopefully this helps everyone out. It definitely corrects some of my semantics regarding what is heat, but the underlying point I was making remains the same. We need to be looking at an energy budget, and the only real loss we can have is radiative, since conductive loss is not possible due to the surrounding vacuum.

holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)
"...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)

This message is a reply to:
 Message 70 by TheLiteralist, posted 03-07-2005 5:43 AM TheLiteralist has not replied

  
JonF
Member (Idle past 167 days)
Posts: 6174
Joined: 06-23-2003


Message 72 of 148 (190445)
03-07-2005 9:57 AM
Reply to: Message 56 by TheLiteralist
03-07-2005 12:36 AM


Re: The Physics of It?
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.
"L" is not a constant, it's a function of the temperature of the Earth's surface and atmosphere, which is itself a function of the rate of heat transfer from the interior (and other things). The rato of heat transfer from the interior depends on lots of complex stuff. One of the several inadequacies of early models is that they didn't realize that the the mantle, although solid, is plastic enough to transfer a lot of heat by convection, which is much more efficient than conduction. The amount of heat lost through the Earthss surface is very different for the continents than it is for the ocean, mostly because oceanic crust is much thinner than continental crusst.

This message is a reply to:
 Message 56 by TheLiteralist, posted 03-07-2005 12:36 AM TheLiteralist has replied

Replies to this message:
 Message 74 by TheLiteralist, posted 03-07-2005 10:08 AM JonF has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 73 of 148 (190446)
03-07-2005 9:57 AM
Reply to: Message 64 by Sylas
03-07-2005 4:45 AM


Re: Kinetic Energy vs. Light Energy
Sylas writes:
From heat at hyperphysics;
quote:
Heat may be defined as energy in transit from a high temperature object to a lower temperature object. An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy. The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object - this is properly called heating.
I can see where your definition is more encompassing and descriptive, but I think it is vulnerable to easy misinterpretation by non-experts. Rather than elevating the discussion to a level where few can follow (including me), it might work better to stay at a layman's level.
I think the layman's level understanding of heat is still pretty accurate, so maybe you can describe where you find fault with this. Heat is the motion of molecules, and the hotter an object, the more rapidly its molecules move. Moving molecules possess kinetic energy. A molecule can give up some of this kinetic energy by emitting photons (EMR), often at infrared frequencies. A molecule can increase its kinetic energy by receiving photons. EMR is not heat. A photon is not heat. While a photon is definitely "energy in transit", it is not heat, and this is where I thought your definition was most open to misinterpretation.
--Percy

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TheLiteralist
Inactive Member


Message 74 of 148 (190448)
03-07-2005 10:08 AM
Reply to: Message 72 by JonF
03-07-2005 9:57 AM


Losing Heat
JonF,
Okay. But couldn't the rate of energy being lost to space from the outer atmosphere be directly measured? Perhaps measured over time just in case it is cyclical or is on a curve (not a constant rate). Wouldn't this negate the need to find out all the complex mechanisms of HOW the heat got to and through the upper atmosphere?
I mean maybe it wouldn't...but I thought maybe it could.
Thanks for the reply and discussion of it, at any rate.
--TheLit
This message has been edited by TheLiteralist, 03-07-2005 10:09 AM

This message is a reply to:
 Message 72 by JonF, posted 03-07-2005 9:57 AM JonF has replied

Replies to this message:
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JonF
Member (Idle past 167 days)
Posts: 6174
Joined: 06-23-2003


Message 75 of 148 (190453)
03-07-2005 10:41 AM
Reply to: Message 74 by TheLiteralist
03-07-2005 10:08 AM


Re: Losing Heat
But couldn't the rate of energy being lost to space from the outer atmosphere be directly measured? Perhaps measured over time just in case it is cyclical or is on a curve (not a constant rate). Wouldn't this negate the need to find out all the complex mechanisms of HOW the heat got to and through the upper atmosphere?
Yup .. but you're going to have to wait a few hundred thousand years or more to get an accurate set of measurments for predicting what happens next, and maybe not even by then. We know it's non-constant and at least approximately cyclical. There's a whole group of periodic changes that together are called the Milankovitch cycles,and the period of the overall sum of those cycles is way up there. The Earth's orbit changes over time; the largest frequency component is at 100,000,000 years with strong components at 43,000 years and 413,000,000 years. See Milankovitch cycles and ice ages, especially figure 2.2. The precession of the Earth's axis and the tilt of the Earth's axis from the orbital plane also vary cyclically.
AFAIK climatologists think that Milankovitch cycles are far from the whole story, but they are definitely important. There's feedback mechanisms that amplify changes.

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