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Why is the Temperature of Water Low Than Atmosphere?

  1. Apr 10, 2012 #1
    Hello guys,
    This has been my observation and a general physical significance of water, maybe.
    I would like to know, why does the water keep its temperature low from the atmospheric temperature?
    For example, the room temperature is 29°C and the water kept in steel bucket may measure somewhat lower, 26°C (Say).
    So what are the factors responsible for it?
    Thank You.
     
  2. jcsd
  3. Apr 10, 2012 #2

    haruspex

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    At the surface of the water, the more energetic molecules are escaping (evaporating).
    If the relative humidity is less than 100%, more are evaporating than are recondensing from the atmosphere. But that is taking heat energy from the water, so the temperature drops.
    Equilibrium is restored when the partial pressure of water vapour in the air equals the saturation vapour pressure of water at the temperature of the water.
     
  4. Apr 10, 2012 #3
    Thanks a lot. Got it, so the heated water will be evaporated. And the cooler will be remain at bottom. This cycle will be continued... Thanks again.
     
  5. Apr 10, 2012 #4

    russ_watters

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    That's not what was said. It isn't a matter of selection of the warmer molecules, it is a matter of energy transfer. Selection may play a role in which molecules evaporate, but the temperature drops because of the heat of vaporization.
     
  6. Apr 10, 2012 #5
    Thanks got the point.
     
  7. Apr 10, 2012 #6
    This is evaporative cooling:
    http://en.wikipedia.org/wiki/Evaporative_cooling#Physical_principles

    http://en.wikipedia.org/wiki/Wet-bulb_temperature
     
  8. Apr 10, 2012 #7

    K^2

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    It's both, actually. Energy barrier acts as both the selector for faster molecules, and to reduce the overall thermal energy. Without both of these mechanisms in place, the equilibrium state would be for both water and air to reach the same temperature.
     
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