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G4CJC > TECH 01.02.04 16:37l 36 Lines 1448 Bytes #999 (0) @ WW
BID : 820336G4CJC
Read: DB0FHN GUEST
Subj: Re: Physics. 3 Questions.
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<GB7TUT
Sent: 040201/1346Z @:GB7TUT.#32.GBR.EU #:2033 [67570] FBB7.01.35 alpha
From: G4CJC@GB7TUT.#32.GBR.EU
To : TECH@WW
> VK3ABK wrote:-
>> By the way, I am disapointed with the non-replies to a comment from Ralph,
>> VK2ZRG, about a black car in a hot country. 'To Man' - 'More stupidity'.
>> Has anyone wandered through a supermarket car park on a sunny day, touching
>> the roof of various coloured cars? Of course not; but try it for science.
>
> I well remember Mr Cook our Science teacher, having a stoppered black can and
> a white can on the front bench with bunsen burners under them. After a while
> one of them imploded. Guess which one. This was accompanied by a lecture on
> kepis and white suits in deserts and how colours make a difference in
> temperature extremes. It made the desired impression.
>
> 73 - Jeff, G4XNH @ GB7YKS
Imploded?? You mean some time after the bunsen burners were turned off?
Even so both cans would lose heat much more quickly by conduction and
convection than by radiation as to make it easy to fudge the desired
result or indeed either result. Any way the demo needs water in the can
and real care with the seal on the on the screw lid. It is intended to
show the effect of air pressure on the can rather than black radiating (or
absorbing) heat best. There are much better demos for showing that heat is
radiated best by a black surface, Leslie's Cube for example.
73 - Tony, G4CJC @ GB7TUT
Message timed: 12:59 on 2004-Feb-01
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