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ruveyn
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11 Mar 2009, 3:53 pm

DNForrest wrote:
Death_of_Pathos wrote:
Woah, electromagnetic radiation is not heat. It can be a method of transferring heat, but radiation itself is not heat. Saying it is heat is as sensible as saying "the temperature of yellow".


I have four separate Chemical and Mechanical Engineering textbooks within two feet of me that would disagree with you. No, not all electromagnetic radiation transfers heat directly, but to say the energy the infrared radiation the sun gives off isn't heat is to say energy given off by conduction and convection isn't heat. The sun loses energy giving off said radiation, we gain energy and increase in temperature until it's given off or stored in some other manner. Sure sounds like heat to me.

This may just come down our ASD tendency to argue arbitrary and tiny points, so let us just agree on the following equation.

Kittens = Poptarts


Heat is energy that is transferred because of a temperature difference.

Infrared radiation is a kind of light.

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DNForrest
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11 Mar 2009, 4:07 pm

ruveyn wrote:
Heat is energy that is transferred because of a temperature difference.


Not necessarily, in terms of conduction and convection, you can say that, but in terms of radiation, two bodies of an equal temperature in a closed system will constantly radiate off heat, but remain in a state of temperature equilibrium (giving off as much heat as they receive, and thus remaining the same temperature).

But, again, this is just splitting hairs.



ruveyn
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11 Mar 2009, 7:46 pm

DNForrest wrote:
ruveyn wrote:
Heat is energy that is transferred because of a temperature difference.


Not necessarily, in terms of conduction and convection, you can say that, but in terms of radiation, two bodies of an equal temperature in a closed system will constantly radiate off heat, but remain in a state of temperature equilibrium (giving off as much heat as they receive, and thus remaining the same temperature).

But, again, this is just splitting hairs.


Put two bodies of equal temperature in contact and see how much heat is transferred from one to the other.

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DNForrest
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11 Mar 2009, 9:40 pm

ruveyn wrote:
DNForrest wrote:
ruveyn wrote:
Heat is energy that is transferred because of a temperature difference.


Not necessarily, in terms of conduction and convection, you can say that, but in terms of radiation, two bodies of an equal temperature in a closed system will constantly radiate off heat, but remain in a state of temperature equilibrium (giving off as much heat as they receive, and thus remaining the same temperature).

But, again, this is just splitting hairs.


Put two bodies of equal temperature in contact and see how much heat is transferred from one to the other.

ruveyn


How much training in Heat Transfer do you have? I ask this because putting the two into contact to transfer heat would be conduction, which I said could fall under what you said (admittedly my wording could have been better). Though in reality, there still is a constant heat flux between the two in equilibrium, even with the same temperature. But, to make things simpler, we just assume that them being the same temperature means no heat is conducted, that they're under ideal conditions (which we all know doesn't really exist).

Neat thing, too, when conducting between two bodies in contact like that, you use the same type of equation for calculating the heat transfer rate that you'd use for calculating the resistance of a current in a circuit.



ruveyn
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12 Mar 2009, 4:00 am

DNForrest wrote:

How much training in Heat Transfer do you have? I ask this because putting the two into contact to transfer heat would be conduction, which I said could fall under what you said (admittedly my wording could have been better). Though in reality, there still is a constant heat flux between the two in equilibrium, even with the same temperature. But, to make things simpler, we just assume that them being the same temperature means no heat is conducted, that they're under ideal conditions (which we all know doesn't really exist).



Enough to know that heat (Q) only flows (without work) from the body with the higher temperature to the body with the lower temperature. There is no natural heat flow between bodies in thermodynamic equilibrium.

heat (ht)
n. Physics
1.
a. A form of energy associated with the motion of atoms or molecules and capable of being transmitted through solid and fluid media by conduction, through fluid media by convection, and through empty space by radiation.
b. The transfer of energy from one body to another as a result of a difference in temperature or a change in phase.

If you want to talk about electromagnetic radiation, that is a different story.

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ZiiP
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12 Mar 2009, 3:47 pm

DNForrest wrote:
ruveyn wrote:
DNForrest wrote:
ruveyn wrote:
Heat is energy that is transferred because of a temperature difference.


Not necessarily, in terms of conduction and convection, you can say that, but in terms of radiation, two bodies of an equal temperature in a closed system will constantly radiate off heat, but remain in a state of temperature equilibrium (giving off as much heat as they receive, and thus remaining the same temperature).
But, again, this is just splitting hairs.


Put two bodies of equal temperature in contact and see how much heat is transferred from one to the other.
ruveyn


How much training in Heat Transfer do you have? I ask this because putting the two into contact to transfer heat would be conduction, which I said could fall under what you said (admittedly my wording could have been better). Though in reality, there still is a constant heat flux between the two in equilibrium, even with the same temperature. But, to make things simpler, we just assume that them being the same temperature means no heat is conducted, that they're under ideal conditions (which we all know doesn't really exist).

Neat thing, too, when conducting between two bodies in contact like that, you use the same type of equation for calculating the heat transfer rate that you'd use for calculating the resistance of a current in a circuit.


May I split some hairs for you? Heat is a perception of energy similar to color being a perception of electromagnetic radiation of some specific wavelength. At least in my profession, the word 'heat' is considered to be a colloquial term used to familiarize the forms of energy that can be associated with fire but is not covered by light, sound or pressure sensation.

At thermal equilibrium, energy may transfer freely between subsystems as long as the net energy change is zero. Because the system is composed of a statistical number of subsystems, some subsystems may have slightly more (or less) energy than the statistical average. The duration of such a microstate is limited by the Heisenberg uncertainty principle. If you follow a specific subsystem with time, you will find that its energy randomly changes around a statistical average. In equilibrium, the net energy change of the system is zero even if the energy of some subsystems take extreme values for brief moments.

For black body radiation in vacuum, both objects will emit and absorb equal amounts of radiation in equilibrium (both of the same temperature). There will be two heat flux components that neutralize each other to give off a net zero heat flux.

For two objects with a medium between them, the medium may also transfer energy from one object to the other. Due to the particle nature of the medium, conduction is always the net effect of microscopic transfer of momentum between particles. Conduction is therefore not possible to go in both directions at the same time, but will be zero by definition if the objects are in equilibrium. There is only one term of conductive heat flux and it is zero at equilibrium.

The difference is that while radiation has an origin and a direction, conduction do not.



DNForrest
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13 Mar 2009, 3:20 am

We seem to be arguing that we agree with each other, or at least the way we've been writing seems that way to me.

Yes, I'm agreeing with both of you. Ruveyn, I was just unnecessarily pointing out that that definition's regarding to ideal conditions. Even in the realistic conditions the net heat exchange is zero. So there is heat exchange going back and forth, it just cancels itself out and/or is so immaterial it's left out of any calculations, and is therefore ignored.

More unnecessarification:
Remember, temperature is defined as "the average kinetic energy of a system", meaning that all of the atoms and molecules of a system aren't actually the same temperature, you're just looking at the average. If you know the physical properties of a material, you can calculate the percentages of particles that fall into a certain temperature range (either above or below the system temp). These things are always fluxing, constantly changing which particles have which temperature, while the average temperature of the whole remains the same. But, again, these things are usually just ignored, because they don't really matter on the large scale. The only time I've ever seen it matter is in the production of nanostructures.



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14 Mar 2009, 2:58 am

twoshots wrote:
DNForrest wrote:
Fuzzy wrote:
However, its heat doesnt reach us. What we get is thermal effects from the increased radiation(light, infrared, et al).


That is its heat. There are three types of heat transfer: conduction, convection, and radiation.

From what I understand, astronomers believe we are in a solar cooling phase having to do with solar flare activity and such, but global warming is still occurring none-the-less from all the greenhouse gas accumulation. Though this has less to do with the average temperature of the sun than the amount of its heat that reaches us, methinks.

Please tell me you can find a citation for that. I'm getting so sick of the "argument from the sun" among global warming skeptics, and I need something definitive to knock them off their feet.


global dimming:

the pollution linked to CO2 emissions in earlier decades reflected some of the heat energy from the sun, slowing climate change but reducing the sunlight available to plants and plankton, thus affecting the food chain.

today we have cleaned up some of that pollution and continue cleaning up, while CO2 emissions continued to rise. This is the reason for the recent deadly heatwaves in australia and europe, for example.

When air travel was grounded in the days after 9/11, and pollution from aircraft (including contrails) cleared up, the average temperature soared by +2 degrees celsius... and reversed a few days after air travel resumed.


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lau
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14 Mar 2009, 9:52 am

Ahaseurus2000 wrote:
...
When air travel was grounded in the days after 9/11, and pollution from aircraft (including contrails) cleared up, the average temperature soared by +2 degrees celsius... and reversed a few days after air travel resumed.

I'm assuming that was meant to be funny. It made me laugh, at any rate. Thanks.


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ruveyn
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14 Mar 2009, 10:17 am

lau wrote:
Ahaseurus2000 wrote:
...
When air travel was grounded in the days after 9/11, and pollution from aircraft (including contrails) cleared up, the average temperature soared by +2 degrees celsius... and reversed a few days after air travel resumed.

I'm assuming that was meant to be funny. It made me laugh, at any rate. Thanks.


It happens to be true.

ruveyn



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24 Mar 2009, 2:29 pm

Ziip is right.
I often read everything that happens within the science community as I am a science geek.
Global Warming is fake.
Humans account for such a small amount of CO2 that it is less than 1%....
It's just a regular sunspot cycle.
Plus we have had the poles shift a bit and that is causing warm places to cool and cold places to warm....