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Hot water feels cold

  1. Sep 12, 2007 #1


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    If you suddenly put your hand into very hot water it feels cold (or atleast, it's hard to tell if it's hot or cold) for the first second.
    Why is this so?
  2. jcsd
  3. Sep 12, 2007 #2
    I guess it's because of two things: Firstly the transfer of energy from the "hot" particles in the water to your hand. Tempreture is a measure of kinetic energy of particles. A hotter tempreture means a greater velocity of the particles. For heat to be transferred the kinetic energy must be transferred to your hand for collisions, also heat needs to be transferred through yourbody tissue which has a poor thermal conductance. Although there were be a slight lag between your hand heating up from the water it would be very slight. I pressume much of the time difference is due to impulses traveling to and from the brain to tell your body that the water is hot.
  4. Sep 12, 2007 #3


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    This would be better in a biology forum I suspect. I read or heard somewhere a few years back that its hard for your nervous system to tell the difference between very hot and very cold objects. Thats why it sometimes feels like you've been burned when you touch something very cold, and why you think hot water is cold when you first put your hand under it. Unfortunately I don't know any of the details, hence a move to a biology forum might be best.
  5. Sep 12, 2007 #4
    Google "the cold/hot grille illusion." It is an interesting tactile hallucination. I think there's a wikipedia on it.
  6. Sep 12, 2007 #5


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    Yes, it has something to do with the fact that both nerves are stimulated, but one of them travels slightly faster and reaches the brain milliseconds sooner.
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