Tuesday, September 11, 2012

MrsDrPoe: Why Is There Dew?

Since I've been spending all my time trying to finish my school work and doing baby things, I haven't had nearly the time I would like to blog faithfully...especially on Thesis Tuesdays!  But I had a special request for today's post- (simply) addressing the question of why there's dew on the ground in the morning.

The answer lies in saturation- a concept that every southerner knows about, even if you don't think you do:  

When Mr. Poe and I make sweet tea, we mix in a heaping two cups of sugar.  If we stir in the sugar while the tea is still warm, all of the sugar dissolves in the liquid.  If we wait until after we put ice in the tea to stir in the sugar, we end up with undissolved sugar at the bottom of the pitcher because the tea is saturated- it's full of sugar and won't hold any more at this cooler temperature.

The same is true with the air.  Also as every southerner knows, the air contains water (in gas form); the amount of water in the air at any given time is what we know as humidity.  

As the temperature of the air drops at night, the air becomes saturated (just like the tea at a cooler temp), and can't hold the same amount of water as it could before.  This extra water condenses, returning to it's liquid form on the ground as dew.  The next day, when the temperature of the air increases again, the dew evaporates back into the air.

And THAT is why we have dew. 


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