# Physics teaser

Discussion in 'Physics' started by studiot, Mar 11, 2009.

1. ### studiot Thread Starter AAC Fanatic!

Nov 9, 2007
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OK so Newton's law of cooling says that the rate of cooling is proportional to the temperature difference and Fourier's Law says that the rate of heat transfer is proportional to the temperature gradient.

Descibe a situation where these laws don't apply.

2. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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Phase II liquid helium!

eric

3. ### studiot Thread Starter AAC Fanatic!

Nov 9, 2007
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Well go on.

My examples are more directly applicable to electronics.

4. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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I believe a Peltier junction may qualify. Will dig deeper.

eric

5. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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Actually, this would apply to any material in a superconductive state

6. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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I believe it would a apply in a perfect vacuum, as well.

7. ### studiot Thread Starter AAC Fanatic!

Nov 9, 2007
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When you are at the bottom of a hole - stop digging!

None of your examples are of something cooling per se.
The question is about cooling / heat transfer, not objects.

8. ### Ratch New Member

Mar 20, 2007
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studiot,

Newton's Law of Cooling if for convection, and Fourier's Law of Cooling is for conduction. So neither of those methods work in a isolated vacuum, such as outer space or a vacuum chamber. Gotta go with radiation if you want to dissipate heat energy in those places.

Ratch

9. ### jpanhalt Expert

Jan 18, 2008
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It just occurred to me that if one clue is zero gravity and the other is dig deeper, maybe studiot is talking about the gravitational center of the earth.

John

10. ### studiot Thread Starter AAC Fanatic!

Nov 9, 2007
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I was thinking about my cup of java actually.

11. ### jpanhalt Expert

Jan 18, 2008
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What is going on with this thread and deletions of several posts?

Is it the moderators or something fluky?

John

May 16, 2005
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13. ### BillO Distinguished Member

Nov 24, 2008
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Are you referring to free convection?

Nov 9, 2007
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15. ### studiot Thread Starter AAC Fanatic!

Nov 9, 2007
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I had a laptop in for service recently and was suprised that in discussion with a technician, who knows a deal more than I about laptops in general and this model in particular, he was clueless about the cooling system.
There have also been quite a few threads recently where members demonstrated a shaky grasp of matters thermal and their connection to electronics so I thought I would start a discussion.

Here is another one from today

So if you would like to apply my question to something no more esoteric than my cup of coffee and thence to practical electronic applications, fire away.

I am aware of the five fourths power law and the experiments by Ezer, Griffiths and Davies; Langmuir, Dulong & Petit etc and also the theoretical work by Lorenz.
I am not talking about any of this or fancy exceptions or refined theories and am sure that there are many more exceptions than the important one I was originally thinking of.

16. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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While we're all rumiinating on the original post, here's another teaser in a similar vein. This is a pure thought experiment.

Let's say there's only one object in space. There are no other stars or other reference points. Can you tell if that object is spinning around its own axis? Does spin even have any meaning without outside references? How would you measure it? Or is spin only a RELATIVE parameter?

Eric

17. ### beenthere Retired Moderator

Apr 20, 2004
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To be very literal, if that object really is the only thing in the universe, then an entity of the class you can't also exist to perform the measurement.

18. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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Let's say "you" are really small and skinny compared to the spinning object. Your bag of test equipment also has no appreciable mass.

eric

19. ### steveb Senior Member

Jul 3, 2008
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If the object is at a temperature above absolute zero, then you can look at the red shift in the black body radiation. The side spinning away from you will have the most red shift and the side spinning toward you will have a blue shift. Hence, spin can not be a relative parameter.

If you are allowed to locate yourself on the spinning object, then there would be other observable effects; for example Coriolis force.

20. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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The coriolis force would be the direct method. If the spinning object were a blob of pizza dough, it would be flattened if spinning. No spin=spherical blob.

There are some really disturbing implications of this, by the way. One is tempted to believe the Ether DOES exist, after all!

eric