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Thread: Cold absorbs rather than applying

  1. #1 Cold absorbs rather than applying 
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    This is an obtuse question, I realize that, but I can't seem to get it out of my head. I remember, when I was in school, my father and my science teachers saying "remember, cold absorbs heat rather than applying cold". I can't understand why that is an important thing to remember. For what reasons would I need to know this? At what point is that an important thing to remember? It's probably something obvious and rediculous...Anyone?


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    Forum Masters Degree Numsgil's Avatar
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    It probably doesn't actually matter in a practical engineering sense. Like with electrical current being the flow of positive charges in some traditions, even though it's really the flow of negative charges.

    The truth is that a hot object leaks energy to a cold object, but thinking of it as a cold object leaking cold to a hot object amounts to the same thing in our macroscopic world. It might matter if you're dealing with things on the quantum level; I couldn't say.


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    WYSIWYG Moderator marnixR's Avatar
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    i think this thread is better placed under physics
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Moderator Moderator Dishmaster's Avatar
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    It reflects a basic physical principle saying that energy gradients tend to average out in time. Temperature is a macroscopic quantity representing a statistical average over the kinetic energies of particles, so a high temperature means a higher average energetic state than a low temperature. If a hot ensemble meets a cold ensemble of particles (any physical body) the kinetic energies of both reservoirs average out, i.e. the faster particles transfer their energy towards the slower particles. Therefore, one could say for simplicity that "cold absorbs heat". The other way around just makes no sense.
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    Forum Masters Degree organic god's Avatar
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    basic application of the second law of thermodynamics, heat does spontaneosly flow from a cold source to a hot source
    everything is mathematical.
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    Forum Masters Degree Numsgil's Avatar
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    Quote Originally Posted by organic god
    basic application of the second law of thermodynamics, heat does spontaneosly flow from a cold source to a hot source
    That's not really the issue. It'd be better to think about it as: does "antiheat" flow from a cold source to a hot source? Obviously the answer is no, but are there any material differences in this interpretation compared to reality? At what point does it make a difference to an engineer? To a physicist?
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  8. #7  
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    The very practical reason to distinguish between source of heat and the recipient of heat as opposed to absorbing, because it than allows you to delve into the actual mechanism for the energy exchange. For example if the energy exchange is due to radiation there are excellent models to estimate the amount radiated by the source (e.g. Planck’s law), we well as that received based on distance from the source, reflection of the receiving object, reemission of receiving object etc.
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    I think it could be compared to vacuum. Within certain limits, you can pretend vacuum is a positive number, and treat it like pressure, but then it can't get any "bigger" than the atmospheric pressure. So, when you get close to a perfect vacuum, it makes less sense to think of it that way. The same thing happens with absolute zero temperature. If someting is at 0 K you can't add any more "cold" to it.
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    Forum Senior Booms's Avatar
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    like most of school taught knowledge the information is barely relevant and at least partially wrong


    Cold 'absorbs' not 'applies' heat is simply an adequate description to explain further complex knowledge I assume


    cold nether absorbs nor applies heat since technically cold does not exist, in the same way black does not exist, cold is simply an absence of heat. when you touch something cold you arn't touching something cold, your skin is simply losing heat exceptionally fast to an object with less heat




    really the whole idea is fairly pointless. either you go on with normal life and it beomes irrelevant or you go into quantum physics (and see just how deep the rabbit hole goes ) and learn that actually there is no hot or cold only slower and faster moving particles that arn't really particles or waves and potentially don't even exist and are only a representation of something that may or may not be the fundamentals of our existance and proof of god the big bang and life itself.... which also might not be real.
    It's not how many questions you ask, but the answers you get - Booms

    This is the Acadamy of Science! we don't need to 'prove' anything!
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    Moderator Moderator Dishmaster's Avatar
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    Quote Originally Posted by Booms
    Cold 'absorbs' not 'applies' heat is simply an adequate description to explain further complex knowledge I assume

    cold nether absorbs nor applies heat since technically cold does not exist, ...
    Okay okay, let's say, "less warm bodies absorb the heat of hotter bodies (purely physically speaking of course)". "Cold" is just a common language expression for something that is less hot than something else, i.e. it is a relative property. Temperature, on the other hand, is an absolute property with an absolute zero point at which theoretically all movement stops.
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  12. #11  
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    Quote Originally Posted by Booms

    really the whole idea is fairly pointless. either you go on with normal life and it beomes irrelevant or you go into quantum physics (and see just how deep the rabbit hole goes ) and learn that actually there is no hot or cold only slower and faster moving particles that arn't really particles or waves and potentially don't even exist and are only a representation of something that may or may not be the fundamentals of our existance and proof of god the big bang and life itself.... which also might not be real.
    I guess if normal life includes learning concepts that can't be expanded to understanding how things actually work that's true. It just easier to learn and frame things properly so it isn't such a leap to a wide group of fields--not just physics. An ancient quote about living an unexamined life comes to mind.
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