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#19
Sunday, February 19, 2012
 azeegum Senior Member Join Date: Nov 2009 Location: Karachi Posts: 443 Thanks: 416 Thanked 345 Times in 197 Posts

Quote:
 Originally Posted by chemguy @Azeegum: 1. I agree that heat can be made from friction and viscosity. And heat can come from many other sources, I guess in my ignorance I was forcing my limited study of heat (thermodynamic perspective) to be the only meaning of heat. 2. "Heat is energy produced or transferred from one body, region, set of components, or thermodynamic system to another in any way other than as work." Your definition is incomplete because if you think about light energy, it can be transferred without any work. 3. What about heat transfer through radiation? Take the whole light spectrum, VIBGYOR along with U.V. and Gamma Newton's Law of Cooling: Newton's Law of Cooling is a very general law and it is not limited to convection. It accounts for all 3 modes of heat transfer because it has only 2 parameters 'Temperature' and 'Time'. And if you know a body's initial temperature, you can calculate its 'k' a constant unique to it which is its overall ability of heat transfer, you can calculate its temperature sometime in future. P.S.:We're splitting hair here :p The original question has been answered several times. But bro, thanks for clarifying this concept!
You're misquoting and misunderstanding me here.
All three answers separately made by you to my posts are apparently self-contradictory. On the one hand you're admitting that heat does not only occur by transfer but also its production. On the other hand, you think that that definition of heat as given by me is incomplete. And yet in another answer, you're going against what you claim in your second answer.
First of all let us read the definition of heat here.
http://en.wikipedia.org/wiki/Heat Read the introductory lines of article.
Now let me make it more clear...
Heat is an energy transferred or produced by any means other than work. Work is an exception to it. I didn't mean that heat as caused by work is also termed as heat according to its standard definition.
And transfer of heat through radiation is spontaneous. And not just radiation, all other means of heat transfer like convection, conduction etc are spontaneous, that is they do not require to have been caused by work to be called as heat as given in definition.
Transfer of heat from sun to earth (ie radiation) is again a phenomenon of transfer of energy. It can not be termed as energy in motion or move. Energy does not move itself. To term energy in motion, is a tantamount to rejecting the standard definition of kinetic energy. Kinetic energy is defined as
"The Kinetic energy (KE) is the energy an object possesses because it is in motion. Moving cars, falling bricks, and vibrating molecules all have kinetic energy. Be careful: it is not energy in motion, or energy going from one place to another, it is the energy something has just because it is in motion."
Visit the source: Heat and Energy

Newton's Law of Cooling
No ! The said law only accounts for convection of heat.
Infact Newton's Law of Cooling particularly describes the cooling of a warmer object to the cooler temperature of the environment which is only carried out through convection. Convection is a mode of heat transfer through liquids and gases caused by molecules from hotter body to colder body and vice versa. Let us take for example holding your one hand above the flame of a candle and the other on one side of the flame at the same distance from the flame. The hand above the burner feels more heat than the other. This is because the hot gases from the flame rise when part of the gas is heated and the cold gas moves to take the place of hot gas. This phenomenon is known as convection of heat.
Other example can be given of the earth. At night, the land cools down more quickly than the sea. The hot air over the sea rises and cold air from the land takes its place. The cooling down of earth is convection and you can detect the temperature difference by applying formula of Newton's Law of Cooling. So, in case of Newton's Law of cooling, the temperature of a body drops down because heat flows out of it. The cooling of a hot coffee is also a case of convection. This law does not apply in case of heat conduction.
So in more elaborative terms, the complete definition of Newton's Law of Cooling goes as
"For a body cooling in a draft (ie by forced convection), the rate of heat loss is proportional to the difference in temperatures between the body and its surroundings."
Visit the reference: Newton's Law of Cooling -- from Eric Weisstein's World of Physics
If you still believe that Newton's Law of Cooling also talks about other modes of heat transfer like conduction or diffusion, radiation etc then just give me any example of heat conduction or radiation by applying Newton's Law of Cooling. I don't know if it is possible. If you can prove it then it will add to my knowledge.

And your last lines make me smile Don't worry we're not going to stumble into splitting hair of each other or of ourselves I share what I know and so does everyone including you. It's share and share alike you know.

Regards
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