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From: derr@nisysg.DEC (Peter Derr  NIO/W3  DTN 261-3105)
Newsgroups: net.flame
Subject: Re: Truth in advertising (Ignorance in physics)
Message-ID: <48@decwrl.UUCP>
Date: Thu, 15-Nov-84 09:03:11 EST
Article-I.D.: decwrl.48
Posted: Thu Nov 15 09:03:11 1984
Date-Received: Sat, 17-Nov-84 03:09:26 EST
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
Lines: 42

------------------------

I could not ignore this ignorant rave against so-called ignorance in journalism
when the criticiser himself has the facts exactly backwards. (Or am I missing
some sarcasm?? :-) )


>I still can't believe the ignorance prevailing in journalism today!
>For someone to draw the conclusion that since black cars get hot in
>the sun, then black pots must radiate lots of waste heat is
>incredulous!  This person should have at least consulted a basic
>physics text.

The writer of this article should have consulted a basic physics text.

>Obviously, black absorbs the most heat, as it does not *reflect* light
>rays of any wavelength.  On the other hand, a silver car will reflect
>most light rays (waves?  particles?).

So far so good.

>On the other hand, an object of colour x can only radiate light (read:
>heat) of colour x (i.e. that wavelength).  Therefore, a 100% black pot
>will radiate *no heat* at all.  It will be warm to the touch, though.

WRONG!!!!!!  An object of color x *reflects* light of color x.  The color
(wavelength) of light that an object *radiates* depends on its temperature,
not its color.  The color (or blackness vs. whiteness) of the object determines
what portion of the light (radiation) striking its surface is reflected or 
absorbed.  Furthermore, the color of the object determines what portion of the
object's thermal radiation is reflected back into the object or radiated out.
A black object absorbs heat (radiation) best AND radiates heat the best.
A white object reflects heat (radiation) best and radiates heat the least.
(Why do you think wood stoves are black?) 

	Therefore, the most efficient cooking pot would be black on the bottom 
(to absorb heat) but shiny or white on the top and sides (to avoid wasting 
heat by radiating it out).

					Peter Derr
					...decvax!decwrl!rhea!nisysg!derr