Subject: Re: Old Wives, water droplets was FROST

Robt R Pries
Wed, 14 Nov 2007 08:10:29 PST
Jonathan wrote;

" It doesn't really make sense, as I think about it,
and I suspect you'll
 agree, that the sun's heat would lead to increased
chilling of the
 leaf under where the waterdrop was located--it
wouldn't evaporate any more
 rapidly than the sun's heat caused it to vaporize."

I am a bit on shaky ground since I am not a physical
chemist, but as I understand the phenomenon. Sunlight
can increase evaporation and although there is a
direct relationship between light and evaporation,
calories may be drawn from the surrounding
micro-environment and not just the sunlight as the
water changes state. Since there is a proportionally
huge consumption of calories required some of these
may be drawn from the leaf. The sunlight may not be
the only source of heat for the evaporation and may
facillitate the process by affecting surface tension
and other factors. Thus the immediate area of the leaf
may be chilled because of its donation of heat to the
process. Perhaps we are both saying the same thing.

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