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Physics of Keeping Warm Vs. Keeping Cool...

by TheStatutoryApe
Tags: keeping, physics, warm
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TheStatutoryApe
#1
Apr19-09, 08:43 PM
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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?
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Astronuc
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Apr19-09, 09:00 PM
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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.
humanino
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Apr19-09, 10:02 PM
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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.

Danger
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Apr19-09, 10:06 PM
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Physics of Keeping Warm Vs. Keeping Cool...

Radiative clothing will help. Notice that desert-dwellers wear several layers of clothing, and usually have a white outer coating.
humanino
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Apr19-09, 10:09 PM
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Quote Quote by Danger View Post
Notice that desert-dwellers wear several layers of clothing, and usually have a white outer coating.
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 ?
TheStatutoryApe
#6
Apr20-09, 12:09 AM
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Quote Quote by Astronuc View Post
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.
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.

Quote Quote by humanino View Post
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.
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.

Quote Quote by Danger View Post
Radiative clothing will help. Notice that desert-dwellers wear several layers of clothing, and usually have a white outer coating.
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.
russ_watters
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Apr20-09, 07:45 PM
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Quote Quote by TheStatutoryApe View Post
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.
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.
lisab
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Apr20-09, 08:06 PM
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Quote Quote by humanino View Post
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 ?
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 .
Danger
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Apr20-09, 08:15 PM
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Quote Quote by lisab View Post
But they do eat a lot of it. Why? To warm up, of course .
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.
Math Is Hard
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Apr20-09, 08:40 PM
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Quote Quote by TheStatutoryApe View Post
I'm supposed to be sleeping but I can't because its too damn Hot!
I hear ya. 90 degrees in my apartment right now. I'll be sleeping under wet towels tonight.
rootX
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Apr20-09, 08:42 PM
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I hate summers.

Neither like contact with wet clothes/towels after sweating a bit. I never tried that.
lisab
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Apr20-09, 08:46 PM
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Quote Quote by Math Is Hard View Post
I hear ya. 90 degrees in my apartment right now. I'll be sleeping under wet towels tonight.
Seattle is niiiiiccce . 74 F now, cloudless evening. Aaaaaahhhh (MiH you need to move here....).
Moonbear
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Apr20-09, 08:48 PM
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Quote Quote by Danger View Post
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.
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.
Math Is Hard
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Apr20-09, 08:56 PM
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Quote Quote by lisab View Post
Seattle is niiiiiccce . 74 F now, cloudless evening. Aaaaaahhhh (MiH you need to move here....).
Temptress!!!
Proton Soup
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Apr20-09, 09:36 PM
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Quote Quote by humanino View Post
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 ?
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.
Proton Soup
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Apr20-09, 09:42 PM
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Quote Quote by TheStatutoryApe View Post
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?
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?
JasonRox
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Apr20-09, 11:07 PM
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Quote Quote by Moonbear View Post
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.
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?
Danger
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Apr20-09, 11:59 PM
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Quote Quote by Moonbear View Post
I think it's more a myth than anything else. I've had ice cream on cold days and just felt colder.
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.


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