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Sensing temperature or heat conductivity?

  1. Jul 29, 2005 #1
    Does anyone know how we feel heat when we touch? I ask because I wonder if two different objects of the same temperature will "feel" different to humans simply because of their different heat conductivity. For example if you touch two things that are both at 0 deg C, one is a block of iron and the other is a block of plastic. Will the block of iron feel colder due to its different heat conductivity.
     
  2. jcsd
  3. Aug 1, 2005 #2
    Can anyone explani the neurological mechanism of touch or heat sense?
     
  4. Sep 15, 2005 #3
    i'm no expert at this, but i do know some basics. The heat conductivity does have something to do with it. It will absorb more heat from your body than something that is less conductive. As to the neurological part... usually, you fell something if there is a change, or a stimulus, in the environment, and the brain tells you, basically, that there is a change and how much change there is. But, please, someone correct me if i am wrong...

    but, to you quasi426, i'd say do some research either on touch, or see if there is a similar thread, or wait until someone acknoledges my theory and elaborates.
     
  5. Sep 15, 2005 #4
    I do know that you can "trick out" your nervous system into feeling that something is hotter or colder than it really is. It's a classic experiment first demonstrated by the philosopher John Locke in the 17th century. Basically what you do is get yourself 3 bowls of water. Have the water in one bowl be very cold. Have the water in the second bowl be very hot, and have the water in the third bowl be at "normal" room temperature. Dip your left hand in the very cold bowl and your right hand in the very hot bowl until they reach equilibrium. Then take out both hands and place them in the room temp bowl at the same time. The point of this experiment is that even though the room temp bowl is at a single temperature, our left hand feels the water as hot and our right hand feels that the same water as cold.

    If you were to interpret this further, you could say that our body only experiences relative temperature. For example, if it was a 100 degree day outside and you drank an 80 degree drink you might think the drink was cool, but if it was 40 degrees and you drank the same drink it would taste warm. The point is that our body temperature at any given moment determines whether we interpret the things we come into contact with as being hot and cold.

    Having said that, "conductivity" refers to the *rate* at which a material can transmit heat. So if we touched something that conducts heat very well, a great deal of heat would be transferred to our body and we might feel a jolt. however, if it was a poor conductor of heat then we can touch it for a much longer time before the same level of heat builds up on our skin. To answer your question, iron is a good conductor of heat, so if it was cold and you touched it you would LOSE heat into the iron (warming it up) at a faster rate than if you touched the plastic where the conductivity is much lower. At least that's my understanding of it.
     
  6. Sep 16, 2005 #5

    somasimple

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    Gold Member

    Well,

    it is a bit complicated because heat and cold aren't carried by the same neurons.

    normal heat (<43°C) is processed by C fibres (slow ones)
    If temperature becomes over 43 then an alarm system works with some other C fibres.
    cold is proceeded by delta fibres from 23°C and under.

    Brain perceives heat and cold changes with at least 4/6 °C minutes. Under these rates you have no feeling of temperature (when comprised between 20 and 40)

    Because heat is exchanged more quickly with metal, you feel their heat in a betteer manner.
     
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