[LRflex] Re: OT: Dark Desert Clothes
- From: Philippe Amard <phamard@xxxxxxxxxxxxxx>
- To: leicareflex@xxxxxxxxxxxxx
- Date: Mon, 27 Nov 2006 08:23:38 +0100
Hi,
I really DK about the difference between cotton and synthetic, sorry,
but I will inquire around me.
As to dark colours exchanging heat faster than lighter ones, cf an
excellent programme by the BBC in the Open University series: this is
where I learned about the black and white egg experiment.
Never performed it myself though.
Enjoy the week.
Phileicangemix
Colin Howarth wrote:
>On 26.11.2006, at 18:52, David Young wrote:
>
>
>
>>Aram offered:
>>
>>
>>
>>>Sorry, I am behind in reading. Maybe someone already said this.
>>>I read an article long ago about dark desert clothes. It seems
>>>that the
>>>dark clothes absorb the light and get hot, and this heat cause the
>>>air
>>>inside the clothes, which are loose fitting robes, to get and hot
>>>and rise.
>>>This draws in cooler air underneath and creates a sort of air
>>>conditioning
>>>system - convective cooling. Of course it does not work with a
>>>black three
>>>piece suit.
>>>
>>>
>>Now that's the best (and the only good) explanation for black robes
>>in the desert that I've seen!
>>
>>
>
>This is so much more fun than commenting on photography or pictures....
>
>OK. How would you define "best" and "good" explanations? I would hope
>that the "best" explanation was correct.
>
>I think I read something like Aram's explanation is some google
>search (or wikipedia article) on bedouin robes.
>
>Now, I can follow the argument as far as "this heat cause the air ...
>to get and HOT and rise."
>
>The bit about "draws in cooler air underneath" is true I suppose, but
>misleading. You don't have cooler air inside the robes - we just said
>it was hot. It gets heated up. You might have cool ankles, but a hot
>neck :-) (cool in the sense of normally hot desert air)
>
>I suppose that if there were some sort of air circulation, then that
>would act like a breeze, which would help the sweat evaporate quicker
>which would draw heat from the skin. Still - it would be a pretty
>warm breeze. I believe the article mentioned above said that the
>scientists had found that there was no significant skin temperature
>difference between light and dark-coloured robed subjects.
>
>That might just mean that the mammalian temperature regulation system
>was working - the people in the dark robes sweating more.
>
>I'm not sure why there's a term "convective cooling". You can
>transfer heat energy (e.g. cool down) by radiation or by conduction.
>Convection is what happens to fluids as a result (of non-uniform
>density).
>
>I wonder what this thing about bedouin robes is. Everyone seems to
>assume that it's a really clever trick. Just because lots of people
>do something, doesn't mean it's a sensible thing to do - does it ? :-)
>
>Now, there might be a really good reason for the dark robes - but it
>would be good to hear from a real bedouin (with internet connection).
>
>
>
>>Unfortunately, black also radiates the heat better, which is what
>>causes the M8's "magenta twist" - especially with synthetic fabrics.
>>
>>Does your science wizardry extend to explaining why synthetic fabrics
>>would cause more problems than, say, cotton or wool?
>>
>>
>
>Maybe they get hotter because they don't conduct heat as well (to the
>air) or to the inside of whatever. Maybe they don't let air pass
>through them so easily. Maybe they really are a bit blacker and
>absorb sunlight better? Maybe they don't even cause more problems? :-)
>
>Friends, real science is tricky and best left to scientists. A lot of
>it involves tedious, careful, controlled experiments. Armchair
>science was fine for the ancient greeks - but didn't actually tell
>them much about the real world.
>
>I look forward to the definitive "correct" explanation. :-)
>
>colin
>
>(more scientist than photographer, I'm afraid)
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