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Our body temperature is roughly 37 degrees celsius (that is, when we measure our body temperature externally, by using a thermometer that measures the temperature of our skin usually between our arm and side torso), whereas most of us would say that 25 degrees would be a pretty hot day. Why do we perceive a 25 degree day to be hot, when thermal energy from our 37 degree bodies should be leaving out and entering our surroundings?

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closed as off-topic by ACuriousMind, Hritik Narayan, user36790, John Rennie, RedGrittyBrick Dec 15 '15 at 9:57

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    $\begingroup$ First of all, 25 degrees Celsius isn't that hot. Second of all, I think this is better suited for Biology.SE $\endgroup$ – TanMath Oct 25 '15 at 3:47
  • $\begingroup$ Relatively we should feel cold as heat should leave our bodies...I am not referring to the degree of hotness, but rather the idea that we shouldn't feel hot, but cold. $\endgroup$ – GoodChessPlayer Oct 25 '15 at 4:10
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    $\begingroup$ "Relatively we should feel cold as heat should leave our bodies." No. Human bodies need not merely non-zero cooling but a sufficiently large cooling rate. When temperatures get too high, we feel hot because the cooling is insufficient. $\endgroup$ – John1024 Oct 25 '15 at 4:26
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    $\begingroup$ I'm voting to close this question as off-topic because it is about human perception, not physics. $\endgroup$ – ACuriousMind Dec 15 '15 at 2:40
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You are correct in a sense of thermodynamics. The heat from a human body does indeed leave the body and into the surroundings. The body combats this by burning calories and producing more heat, keeping the internal body at a constant temperature.

I'm not a biologist however:

Perception of a hot day, is just because our nerves our telling our brain its a given temperature. We are warm blooded animals, our body naturally generates heat. Lets assume that the body generates the same amount of heat every day, our brain may interpret a 25C day as warm because the body is generating the same amount of heat however it is leaving the body into the surroundings at a slower rate.

Temperature sensing is a survival tool, it used as a way of keeping the body at a constant temperature. As it gets hotter, your brain is in a sense telling you that it's getting harder to cool. (Forgive my terminology)

Think of this, if the day was as hot as the human body, you would be at danger of heat stroke.

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