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Offline harryneild

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Air friction question
« on: 23/04/2006 21:17:50 »
When i stick my head out of the car window moving at about 30mph, it becomes significantly colder than inside the car, or indeed when i stand outside.
When a shuttle enters earth is becomes immensly hot on the bottom due to air friction.

Why does my face go cold, yet the craft become hotter? Is there a boundary where the heat caused by friction is equal to the heat lost from the wind?

"Knowledge has to be improved, challenged, and increased constantly, or it vanishes." Peter F. Drucker
« Last Edit: 05/04/2007 22:04:56 by harryneild »


 

Offline ukmicky

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Re: Air friction question
« Reply #1 on: 23/04/2006 21:51:22 »
I'M GUESSING

The air down at ground level has lots of moisture in it compared to high up in the atmosphere and in combination with the sweat which your body releases and at speeds that cars move you feel cool as there is not enough friction to burn off the moisture and sweat quickly enough.

If you were to strap a few rockets on to the rear of your car so you were moving more at the speed of the shuttle as it enters the atmosphere and then stick your head out of the window apart from losing your head i promise you wouldn't be feeling very cool for very  long and your face would probably burn off.

Michael
« Last Edit: 23/04/2006 22:13:57 by ukmicky »
 

Offline daveshorts

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Re: Air friction question
« Reply #2 on: 23/04/2006 22:38:17 »
The reason your face goes cold isn't a surplus of moisture in the air but a lack of it, if it was very humid the effect would be much less as the air would be able to absorb less water - why sweating on a very humid day doesn't work and drips off you rather than evaporating. This effect is called wind chill and is caused by the layer of air right next you your skin being changed more quickly in a wind than in still air. In still air the layer of air near your skin gets more moist and warmer as your sweat evaporates and it is in contact with your skin, this will tend to insulate you a bit. If this air is blown away you lose this effect and loose heat quicker so feel cold.

This effect is much larger than the friction at 70mph but at 10 000mph the opposite is true and you would heat up very quickly!!
 

Offline fm47

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Re: Air friction question
« Reply #3 on: 25/04/2006 08:59:28 »
Also, with enough exposure, you can actually get "wind burns".

It becomes colder when the wind blows because it carries away with it your body heat and the bit of heat that surrounds you (ahhh! my personal bubble~~~~~.!..!..!).
The moisture part also plays part.
 

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Re: Air friction question
« Reply #3 on: 25/04/2006 08:59:28 »

 

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