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Treebeard's Stumper Answer
11 Oct 96

The autumnal equinox has come and gone, but it's been HOT this week anyway, and we've had our fans going full-time at home. Fans actually add energy to the air by moving it faster. So doesn't a fan really make the air warmer rather than cooler?

A fan doesn't cool the air that it moves. But it makes the air more cooling by increasing the evaporation of perspiration from our skin. Water vapor is in a higher energy state than liquid water, and that energy has to come from somewhere, namely us. My Mom still(!) tries to talk me into a short haircut every summer, arguing that it will be cooler. But I think she has it wrong. Hair has lots of surface area to allow more evaporation and hence more cooling. I usually get by with a bandanna.

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