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Which is more cooler?

  1. Jun 19, 2012 #1
    ICE at 0 degree C and WATER at 0 degree C.
    Which will appear more cooler to our mouth?
    What factors determine the coldness of a body at same temperature.
     
  2. jcsd
  3. Jun 19, 2012 #2
    Enthalpy of fusion for water is 79.72 cal/g. So ice is colder (it will absorb more energy). But ice cube is bad conductor of heat, therefore 1 g water at 0 degree C may feel cooler.
     
  4. Jun 19, 2012 #3
    Good answer, but we can carry this thought experiment further to see that the ice will feel cooler because it will conduct heat from your mouth more quickly.

    If you put water in your mouth it will immediately start to increase in temperature and feel less cool.

    If you put zero degree ice in your mouth, it will immediately begin to melt. So now you have ice and water in your mouth, but everything stays at zero degrees.
     
  5. Jun 19, 2012 #4
    can u convert it into easy words.
     
  6. Jun 19, 2012 #5

    CWatters

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    In easy words...

    When a material such as water undergoes a change of state (eg ice to water or water to steam) some extra energy has to be added or removed even though the temperature remains unchanged. This energy has various names depending on what the states are and in which direction the change is taking place.

    See also http://en.wikipedia.org/wiki/Latent_heat

    So to the ice vs water question.

    In the case of water: It takes an amount of energy to heat water from 0C to body temperature.

    In the case of ice: It takes an amount of energy to turn the ice to water at 0C AND then an amount of energy to heat water from 0C to body temperature.

    Ice feels colder because the mouth has to deliver this extra energy to the ice to melt it first.

    In years gone past steam engine boilers were prone to exploding. Sure some people were killed by the explosion itself but the survivors had a worse fate... The escaping steam would condense on people releasing a lot of energy as it turns from water vapour at 100C to water at 100C. So people were in effect blasted with heat...and only then were they boiled.

    When you boil a kettle you sometimes get a clear jet or water vapour emerging from the spout and then turning to steam an inch or so away. That clear bit you can't see is more dangerous than the steamy bit because it contains the extra latent heat.
     
  7. Jun 19, 2012 #6

    Nugatory

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    The coldness we feel is determined by how quickly heat flows from us to the cold substance.

    Ice at 0° Celsius will soak up a respectable amount of heat as it melts into water at 0°; it will feel colder.... or at least that's what I feel when I try the experiment.
     
  8. Jun 20, 2012 #7
    I may be wrong to say that water feels colder and I have not done experiment. But this is what I thought:

    When you eat ice cream, it is first few spoons of ice cream that feel colder. Then your mouth being cold is less sensitive to temperature or you are kind of used to coldness in mouth so you don't feel next spoons as cold as first one.
    In case of ice vs water, what matters is how long is time for heat exchange. If you take ice cube of 8 ccm in mouth and think of all time till it melts, first few seconds are significant for feeling coldness. If you take 8 ccc of water at 0 degree C, lot of heat transfer happens in just a second or two. Water touches entire mouth at one go and hence rate of heat transfer is faster. Hence colder feeling.

    Again, this is personal opinion, may be wrong.
     
  9. Jun 20, 2012 #8

    sophiecentaur

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    This is analogous to the 'wind chill factor' whereby stationary cold air doesn't make you as cold as moving air at the same temperature - heat is removed faster so there is a steeper temperature gradient near the surface of your skin and the temperature sensors (below the surface) are actually at a lower temperature and they tell you.
     
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