ELI5: If you have 2 of the same item, one heated to 100deg and one cooled to -100deg. Will their temperatures depreciate at the same rate or is one faster than the other?

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You are missing one component that makes it impossible to know, actually a couple. But mainly, how warm is the room they are in. If the room is at 70 degrees, the 100 degree item will cool slower than the -100 degree item heats up. Because the 70 degree air won’t be able to dissipate the heat as fast as lets say 30 degree air, or -20 degree air. There is still other factors too. For example, not all materials transfer heat and cooling at the same rate. So depending on what material the item was made out of, it might shed heat a lot faster than heat up.


Heat transfer is a really difficult subject with whacky equations governing the details, so the true answer is “it depends on a lot of factors”. The temperature of each object affects the air flow around it, among other things. Heat transfer in a vacuum is not that interesting, so we can not go the typical simplifying route. Generally speaking, the factor that matters most for conductive heat transfer is the temperature of the item relative to its surroundings. In this case, reading your other posts, that is the same. So, their temperature would change at the same rate, and both items will reach equilibrium temperature at the same time. However, the hot item can also cool down due to radiative heat transfer. An object emits more radiative energy if it has a higher absolute temperature. This number scales by T^4. This number may not be that big at 100°, but it is there. tldr; there are too many factors to give a definite answer, but I’d put my money on cooling being very, very marginally faster in most cases.


Also, are they wet? What is the humidity? The cool one might get covered with frost, which would insulate it. The hot one would cool faster when wet if the air isn’t saturated. What color are they? Is the airflow unrestricted, or is the object on a surface? Not enough info, bud


That depends on what the temperature of the room is and if the objects are being exposed to any light. If the objects are dark and being exposed to light then they will both be absorbing energy from that light and so the hot thing will cool down slower than the cold one heats up. But, all else being equal, if the room is at zero degrees then they should reach equilibrium in practically the same time.


So im going to make a couple of assumptions here first. I am going to assume that these objects are metallic in nature and are placed in a nearly perfect vaccum and the “temperature” of this near perfect vaccum is 0deg. In this case, if the material of the bodies are metallic in nature, much of the temperature can be attributed to the kinetic energy of the electrons in the electron kernel. Heat can be transferred, if you ignore quantum mech for now, via conduction, convection and radiation. Since its a near perfect vaccum, the conduction factor is lower. However if you were to consider it, then the electrons with more KE can have more collissions with the particles in the free vaccum to transfer energy, but when you consider the element at – 100deg, the number of collissions between the particles in the vaccum and the ones on the plate are substantially lesser so the heat exchange doesnt happen more. When you take radiation into account, depending upon the reflectivity, emissivity and absorbtivity, the factors change but generally speaking, since objects at a lower temperature (considering a black body approx) radiates and absorbs at a lower rate/higher wavelength, the heat loss from the one at the lower temperature will be lesser. A similar concept also applies for non metallic plates. So technically, the one at the higher temp cools faster than the one at the lower temperature heating up.