Survival in hot deserts has always posed a problem for man;
Moses had to solve it in order to lead the children of Israel through the wilderness of the Sinai—a formidable hot desert.
It seems likely that the present inhabitants of the Sinai,
would have optimised their solutions for desert survival during their long tenure in this desert Yet,
one may have doubts on first encountering Bedouins wearing black robes and herding black goats.
We have therefore investigated whether black robes help the Bedouins to minimise solar heat loads in a hot desert.
This seemed possible because experiments have shown that white hair on cattle1,2 and white feathers on pigeons3 permit greater penetration of short-wave radiation to the skin than black.
more heat flowed inward through white pigeon plumage than through black when both were exposed to simulated solar radiation at wind speeds greater than 3 m s-1 (ref.
We report here that the amount of heat gained by a Bedouin exposed to the hot desert is the same whether he wears a black or a white robe.
The additional heat absorbed by the black robe was lost before it reached the skin.
Another way to look at it is this its like having a FAN - The explanation I heard for this is that the clothes themselves are
very loose (rather like Roman togas).
The extra heat caused by the
black colour causes increased upward convection of the air between
the cloth and their body.
This additional air circulation actually aids in
evaporation of persiration and thus results in better cooling.
another scientist put it like this:
Darker clothes absorb more of the sun`s energy,
so this seems to
make no sense,
say David Halliday et al.
in "Fundamentals of
Physics." In fact,
black robes have been found to be 6 Celsius
degrees hotter than similar white robes.
The Bedouin secret lies in
the convection breeze set up when the warmer air inside a dark robe
rises faster and escapes upward through the porous material,
in air from below.
So a black robe winds up being no hotter,
circulating air may even make things more comfortable.
Notice that a key element in this system working is the convection
made possible by the escape of air through the porous material.
So lukey it really is best to ask mum for help with your homework cos she is a legend and you know it!!!!