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Temperature: Our body and the environment

  1. Jan 4, 2012 #1
    It is generally believed that the normal body temperature of a healthy human adult is around 37.0 degrees C.

    If the temperature of the surroundings in Singapore (tropical equatorial climate) is around 27.0 degrees C, why do humans feel warm when heat is supposed to be leaving the body. (Heat travels from a warmer region to a cooler region).

    This is not a homework question - just a thought that has been in my head for some time.
     
  2. jcsd
  3. Jan 4, 2012 #2

    Danger

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    Welcome to PF, Electrofanner.
    Your specific question sort of answers itself. When something feels warm to you, that is because heat is leaving it and entering you.

    Singapore is only 27°?! Bloody 'ell! I keep my home thermostat at 28°.
     
  4. Jan 4, 2012 #3
    Thanks.

    Quoting: "When something feels warm to you, that is because heat is leaving it and entering you"

    Exactly. This is what perplexes me. Since the temperature of the body is higher than that of the surroundings, shouldn't heat be leaving our body - therefore, shouldn't we feel cold? Instead, I feel warm.

    Yes, Singapore is hot all day/all year. I wish for snow. :D
     
  5. Jan 4, 2012 #4

    Danger

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    You're more than welcome to mine. :grumpy:
    As for the rest...
    All that I can say is that we evolved for evaporative cooling. That's what sweat is all about. When moisture evaporates from our skin, heat is absorbed by it and taken from us.
    I suspect that interpersonal feelings are at least partially emotional in nature. Someone that you love will feel warm to you (at least after a couple of seconds) because feeling him/her is preferable to being out of contact. Someone that you hate, although at the same temperature, will probably feel like a lobster to you because you find physical contact (with that person) repugnant.
     
    Last edited: Jan 4, 2012
  6. Jan 4, 2012 #5
    Temperature of our skin is significantly lower than 37.0 deg. C. Moreover, a man - is a heat-producing machine. If I'm not mistaken heat production of an average adult is about 100 W at rest and may be more than 400 W at hard work. At 27 deg of the air temperature heat transfers to the air, but what is the rate?
     
  7. Jan 4, 2012 #6

    Danger

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    Sorry, Dude; you lost me as soon as the term "work" arose.
    I'm going to have a nap now.
     
  8. Jan 4, 2012 #7
    Sensible temperatures (the temperatures we actually feel) are a very complex subject. They vary from individual to individual and from time to time for any given individual.

    The average adult human is most comfortable at an ambient temperature of 25°C and a relative humidity of 50%. Singapore's mean annual afternoon temperature is more than 27°C Its afternoon humidity averages 74%. Add in the occasional sunshine loading, and this sensible temperature can easily exceed 40°C. You might want to add another 5° to 10° for the urban heat island effect (most noticeable during the nighttime hours).

    Hence the common feeling of oppressive heat.

    Simply comparing air temperature to skin temperature is misleading.
     
  9. Jan 4, 2012 #8

    russ_watters

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    You're confusing what you feel inside your body to what you feel when something outside your body touches you.

    Whether you feel hot or cold is based on if your body temperature is above or below normal - if you are failing to dissipate heat fast enough. The temperature that the air needs to be to dissipate heat from you at the appropriate rate depends on your clothing, your activity level, wind speed and humidity. It could be 10 C outside and you can feel hot if you are wearing a lot of clothing and exercising or you can feel cold while it's 20C outside if it is dry and windy and you aren't wearing much clothing.

    Something you touch - be it an object or the air - will feel cold to you if it makes your skin cooler than normal for your skin. Critical for this is that since your skin is always colder than inside your body and it is always transferring energy to the surroundings, for something to feel cold to you it must transfer heat away from you faster than normal. This is why a room temperature piece of metal feels cold while a room temperature piece of wood does not. The metal transfers heat away from you faster.

    Combining these two concepts, your body can feel hot while at the same time feeling a cold object be cold. Just wear some extra clothing until you start to feel warm, then touch a room temperature piece of metal to demonstrate. Taken to the extreme it can feel very odd, such as if you exercise outside on a cold day. Your skin may feel cold, yet your body can be hot and you can sweat. When I was younger, I would run outside in freezing temperatures wearing shorts, a t-shirt and thin gloves -- and I'd sweat while my skin felt the cold of the air.
     
  10. Jan 6, 2012 #9

    Danger

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    There must be a Canuck hiding somewhere in your family tree.
     
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