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How come the wind is cold?

  1. Jun 19, 2009 #1

    quasar987

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    A windy 0 °C day perceived as colder than a 0 °C day without wind.

    I find that strange, given that wind is just air particles with kinetic energy. When those speedy particle hit a body, they should give off some of their energy to that body in the form of heat. But instead cold is perceived by our skin. How come?!
     
  2. jcsd
  3. Jun 19, 2009 #2
    In still air, your body heat warms the air around you, forming a kind of 'protective' warm layer of air. In hard winds, the air around your body is constantly refreshed, and it gets no chance to warm up. Your body heat literally is 'washed away' by the wind! The energy of the particles hitting you should indeed warm you up a little bit, but I'm sure that effect is immeasurably small in comparison.

    Compare this to what you should do if you burn your finger! I'm sure you've always been told to hold it in cold, flowing water, instead of still water. The reason is basically because still water warms up pretty quickly due to your body heat. Flowing water is still cold when it hits your skin, and it then washes away, making room for more cold water.
     
  4. Jun 19, 2009 #3

    turbo

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    Remember also that cold winter air is often quite dry, and when it hits your skin, it can evaporate water from your skin. Evaporative cooling can make the air feel cooler than it is.
     
  5. Jun 19, 2009 #4

    russ_watters

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    Yes....
    Not if the kinetic energy of the body they hit is higher than theirs! Then the body gives some of its heat to the air particles (molecules).

    And the faster the wind, the more air molecules hit your body, for your body to transfer some of its energy to.
     
  6. Jun 19, 2009 #5
    Yeah I agree with Russ. The heat is transferred from the hotter object (you) to the colder object (the air). Wind just allows more and more of the air which is colder than you to come into contact with you, and leaves no chance for equilibrium between you and the cold air.
     
  7. Jun 19, 2009 #6

    Astronuc

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    Conduction and convection. The wind speed is much, much less than the speed of the air molecules, which is on the order of 400 m/s at 0°C, as compared to a wind of 20 km/h or 5 km/s.
     
  8. Jun 20, 2009 #7
    it takes the heat away from your body quicker.
     
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