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Braddock

Possibly dumb question, But ....

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OK, This question probably has an easy answer, But it escapes me. Someone asked me this recently and I couldnt come up with a convincing answer.

 

Why is it, That on a cold day, Say 20 degrees, Clear skies, That while in your car you can feel the heat of the sun on your face, Yet the window is very cold?

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First of all you must realize that skin is a poor thermometer. It is a much better measure of heat transfer, which is why a piece of metal feels colder than a piece of wood at the same temperature (below body temperature) - the metal conducts heat better away from your skin.

 

There are three types of heat transfer - conduction, convection and radiation. The sun radiates a lot of energy - more than a kW per square meter - and you feel that on your face inside the car. But there is little convection, since there is no wind, and minimal conduction, since air is a gas and doesn't have a large heat capacity.

 

So what you feel is the radiation heat transfer, as the other forms have been reduced.

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Thanx, I knew it was something similar to that. What a cool site Ive found. Ill have to check in each day for interesting topics.

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