Physics of Keeping Warm Vs. Keeping Cool

  1. I'm supposed to be sleeping but I can't because its too damn Hot!

    I've always thought it is easier to keep warm when it is cold out than it is to keep cool when it is hot out.

    Scientifically speaking which is "easier" in a real world scenario and why?
     
  2. jcsd
  3. Astronuc

    Staff: Mentor

    It depends on the heat transfer coefficient and the surrounding temperature, but it's probably easier to keep warm than it is to keep cool, although with A/C it's easy to keep cool. I'm also referring to the person, as opposed to maintaining a room at a given temp.

    For a person, the matter is one of conduction or convection of heat to or from the surrounding atmosphere. For a room or building, it's a matter of the heat transfer by conduction and convection, and that is affected by the insulation (thermal resistance) and temperature differential.

    Russ is the boss in this department.
     
  4. Keeping warm is pretty easy : put on more clothes, make a fire, drink a vodka, dance crazily on the table. I have no idea how to cool down however, apart from having a swimming pool or the sea/ocean nearby.
     
  5. Danger

    Danger 9,878
    Gold Member

    Radiative clothing will help. Notice that desert-dwellers wear several layers of clothing, and usually have a white outer coating.
     
  6. Is it true that they drink very hot tea to reduce the temperature difference between inside and outside ?
    Could I fight cold by eating ice-cream ?
     
  7. Yes, Russ seems to know alot about this subject.
    I understand that there are several variables. Maybe specifying a real world scenario was not the right track for what I'm thinking about. I was wondering if there is some fundamental element of thermodynamics that would explain it and how or whether it applies to a real world scenario with all of the implied variables. So if I have a uniformly cool environment and wish to create and maintain a localized area of heat within that environment is there any reason why that would be "easier" than shedding heat from a localized area in a uniformly warm environment? Now that I think of it in a real world scenario I guess it may be as simple as: Its easier to contain heat in a localized area than to keep ambient heat out of a localized area.

    That's the way I have always seen it. You can add layers for more heat but you can only take so much clothing off to cool down before you are naked.

    I've heard about this too. I suppose it has something to do with the thin faberic and the breath-ability of it creating airflow along with the reflective power of the white.
     
  8. russ_watters

    Staff: Mentor

    humanino's answer really is it. If you're already naked, and you're still too warm, then keeping cool requires more sweating, which makes you feel uncomfortable.
     
  9. lisab

    Staff: Mentor

    I used to live in Alaska, and I worked at an ice cream store. Alaskans are rumored ot eat more ice cream per capita than any other state...yeah I don't believe that for a second, either.

    But they do eat a lot of it. Why? To warm up, of course :tongue2:.
     
  10. Danger

    Danger 9,878
    Gold Member

    That is correct. There's nothing like a hot cup of tea or coffee on a hot day, or an ice-cold beer or pop on a cold day. The input from either tricks the hypothalamus into thinking that it's (in order) hotter or colder than it really is. It therefore ramps up compensatory mechanisms such as sweating in the case of heat or shivering in the case of cold. Both provide immediate relief.
     
  11. Math Is Hard

    Math Is Hard 4,915
    Staff Emeritus
    Science Advisor
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    I hear ya. 90 degrees in my apartment right now. I'll be sleeping under wet towels tonight.
     
  12. I hate summers. :cry:

    Neither like contact with wet clothes/towels after sweating a bit. I never tried that.
     
  13. lisab

    Staff: Mentor

    Seattle is niiiiiccce :smile: . 74 F now, cloudless evening. Aaaaaahhhh (MiH you need to move here....).
     
  14. Moonbear

    Moonbear 12,265
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    I don't think it works that way. If your brain temperature is changing enough from a cup of tea or bowl of ice cream to signal adjustments to body temperature, you've got bigger problems than the weather.

    I think it's more a myth than anything else. I've had ice cream on cold days and just felt colder.

    Though, I have heard what may or may not be another myth, and that's that eating spicy foods is good in hot climates, not just because you can't taste the spoilage of the food as much, but because the spice makes you want to drink more water, so you stay hydrated better.

    Generally, staying warm is easier, because you can add more layers of insulation to prevent your body from losing heat. Cooling is tough, especially if it's humid, because you just can't get enough sweat to evaporate....you'd have to use cool, damp cloths or something to help cool off so you can transfer your body heat to the cooler cloths...or cool tub of water or pool, etc.
     
  15. Math Is Hard

    Math Is Hard 4,915
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    Temptress!!!
     
  16. you get a lot more calories from the ice cream than you expend heating it up. so, yes, it would fight the cold in a roundabout way. it can also warm you up by making you fatter, and thus more insulative.

    anecdotally, i once read that guys on antarctic expeditions would eat butter to warm up. never quite figured that one out. maybe brown fat works best with lipid fuel or something.
     
  17. how to define the question? i think probably, most humans live at temperatures lower than our body temperature, but the temperature at which naked humans feel most comfortable is going to be several degrees lower. so, do more humans live in areas where the average temp is lower or higher than the comfortable nude temp?
     
  18. JasonRox

    JasonRox 2,327
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    Good point. I think it's a myth too.]

    I'm glad I don't live in the south with no air conditionning. I would die. It's hard enough doing that in Ontario nevermind California/Florida. Is that even possible to live the whole summer like that?
     
  19. Danger

    Danger 9,878
    Gold Member

    You are the expert in biology, so I won't dispute you... but I've noticed the effect myself upon uncountable occasions. Perhaps it was psychological—a placebo effect, if you will. Still, a nice cup of tea cools me off.
     
  20. Share? :puppydog eyes:
    Actually I sleep during the day (night job) which makes it much more difficult.

    I've been wanting to move to Portland. I love the rain.
    I hear Seattle is boring though. ;-p

    I was thinking more along the lines of whether its harder to remove heat than produce it. I guess there are ways around that such as using a heat sink like a giant block of ice maybe.

    California isn't actually that bad for the most part. Most of the cities are closer to the coast. We do have some high desert areas though. I hear Louisiana is particularly bad for the heat (+humidity). Which sucks because I have always wanted to go to New Orleans for the Jazz festivals and such. I just can't stand the heat.
     
  21. turbo

    turbo 7,366
    Gold Member

    Good answers regarding the ease of staying warm when it's cool. I'll emphasize one thing that has been mentioned, and that is layers. It's a lot easier to stay warm if you wear light loose-fitting layers. If I'm going to be spending time outdoors in the winter, I'll generally wear a T-shirt, a light, loose flannel shirt, and an over-sized polar-fleece pullover with a thin nylon shell over that. The light loose layers trap body-heat and the outer windbreaker keeps the cold breezes from penetrating the fleece to steal that heat.

    I have some nice winter coats, but rarely wear them unless it is bitterly cold, and I will be forced to be inactive.
     
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