美国科学60秒 SSS 2012-10-15

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Hair helps keep you warm, right? But hair can also keep you cooler than bare skin, as long as the hair is not too thick. So says a study in a journal-Plus One.

 

Reseachers studied elephants which have very thin coats of hair. It's easy for the beasts overheat, they may face temperatures up to 120 degrees Fahrenheit¹, and they don't have much skin surface area to radiate the heat relative to their big body volume. That's where the hair comes in. The reseachers wrote equations modelling the elephants hairy skin. As is expected, the thick hair traps air and keeps the body warm. But below a certain density², hair stops insulating, and wakes heat off the body instead, helping³ the elephants get rid of an extra 20% of their body heat, especially on windless days. Heat sinks inside computers work in a similar way, with pin sticking up to help dissipate the interior heat. The researchers speculate that hair may actually evolve to help animals stay cool, because the first sprouded mammals over a 100 million years ago in a hot climate. Hair raising time indeed.

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