# How do thermoses know if they are supposed to keep drinks hot or cold? **URL:** \ **Category:** Factual Questions\ **Created:** [August 23, 2010, 12:05am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114 "2010-08-23T00:05:05Z")\ **Posts on this page:** 13\ **Page:** 3
**Author:** ![EdwardLost](https://avatars.discourse-cdn.com/v4/letter/e/bbe5ce/32.png) [@EdwardLost](https://boards.straightdope.com/u/EdwardLost)\ **Post date:** [August 23, 2010, 11:46pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/41 "2010-08-23T23:46:20Z")
> [@GHO57](#): > > about the speed of sound? Closer to the speed of quiet. ---
**Author:** ![Biffy\_the\_Elephant\_Shrew](https://avatars.discourse-cdn.com/v4/letter/b/e47c2d/32.png) [@Biffy\_the\_Elephant\_Shrew](https://boards.straightdope.com/u/Biffy_the_Elephant_Shrew)\ **Post date:** [August 23, 2010, 11:52pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/42 "2010-08-23T23:52:00Z")
> [@muldoonthief](#): > > How about Faraday? Experimentalists need love too, you know. He’s so great he should have been king. King Faraday. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 24, 2010, 12:58am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/43 "2010-08-24T00:58:06Z")
> [@carnivorousplant](#): > > They don’t. They prevent the radiation or convection of heat, in or out.🙂 Nitpick; a thermos (particularly a Dewar type flask) maintains a low or high temperature equilibrium inside the container by preventing conduction of heat (transmission through a static continuum). I suppose it can be said that it heat transfer by convection as well by sealing the material inside from allowing air to blow over it, but you can get that same effect by storing it in a Tupperware-type container. It does very little to prevent radiation, and in fact, that is the main avenue for heat transfer in a Dewar flast. However, for most terrestrial temperature gradients in atmosphere, radiative heat transfer is small and conduction is by far the most effective route of heat transfer. Regarding Maxwell, I’d argue that his contributions to modern physics and engineering exceeded that of Albert Einstein, both for their breadth and practical application. Even setting aside his eponymous work on electrodynamics, his contribution to the field of thermodynamics was substantial and notable. If Maxwell had been born a generation or two later, he doubtless would have been on the forefront of quantum mechanics. Stranger ---
**Author:** ![Autolycus](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@Autolycus](https://boards.straightdope.com/u/Autolycus)\ **Post date:** [August 24, 2010, 3:50am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/44 "2010-08-24T03:50:32Z")
If you have enough panes of transparent aluminum, you can turn your entire house into a cooler! Just think of the money you’d save on heating and cooling. ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [August 24, 2010, 11:43am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/45 "2010-08-24T11:43:21Z")
> [@Chronos](#): > > > [@](#): > > > > If you were to consider him the fourth, whom would you consider the third? > > Newton and Einstein are the top two, then maybe Archimedes, then Maxwell. Heisenberg might belong on that list. But I’m not certain. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [August 24, 2010, 11:54am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/46 "2010-08-24T11:54:21Z")
> [@Hypno-Toad](#): > > > [@Chronos](#): > > > > Newton and Einstein are the top two, then maybe Archimedes, then Maxwell. > > Heisenberg might belong on that list. But I’m not certain. I can tell you for how long he should be on it, though. ---
**Author:** ![GHO57](https://avatars.discourse-cdn.com/v4/letter/g/df788c/32.png) [@GHO57](https://boards.straightdope.com/u/GHO57)\ **Post date:** [August 24, 2010, 12:01pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/47 "2010-08-24T12:01:46Z")
> [@Smeghead](#): > > > [@Hypno-Toad](#): > > > > Heisenberg might belong on that list. But I’m not certain. > > I can tell you for how long he should be on it, though. 😃 ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [August 24, 2010, 12:16pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/48 "2010-08-24T12:16:23Z")
> [@Smeghead](#): > > > [@Hypno-Toad](#): > > > > Heisenberg might belong on that list. But I’m not certain. > > I can tell you for how long he should be on it, though. Or where on it. Just not both. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [August 24, 2010, 2:13pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/49 "2010-08-24T14:13:15Z")
As Newton wrote, if he had seen further, it was on the shoulders of giants, Archimedes was the tallest of those giants. (\*) That said, I still remain gobsmaked by the contributions of people such as Archimedes, Newton and Maxwell. Gallieo too. Look at the delta they made in human knowledge. It isn’t just the discoveries they ended with, but what little they started with. (\*) There is a rather uncharitable view of this quote, but I’ll stick to the mainstream one. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 24, 2010, 3:28pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/50 "2010-08-24T15:28:35Z")
Maxwell and Faraday I would think to be ranked due to their being multidisciplinary scientists which is extraordinary by their time. Both Faraday and Maxwell impacted a number of sciences in fundamental ways and that impact was an applied one. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [August 24, 2010, 7:17pm UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/51 "2010-08-24T19:17:05Z")
You’re all wrong. Thermos bottles and Dewar flasks all know if they are supposed to keep drinks hot or cold by the temperature of the material put inside them and by the temperature of the surrounding air or water. When these containers are built, a small brain-like device is put in the bottom, sort of like a drain but with no holes, and, of course, spelled differently. This brain-like device takes into account the temperature of the surroundings and the temperature of the material put inside, and is able to determine by these two figures, what your intentions are. Once this is calculated, and it’s done very very quickly - in a matter of minutes - the thermos begins to do its work and it is then set to function as a cooler or as a warmer protector. The person who invented this device was the same one who invented those signs at the mall that tell you, “You are here.” Those signs happen to be equipped with devices that can actually tell where you are. Isn’t science wonderful? ---
**Author:** ![Jenaroph](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Jenaroph](https://boards.straightdope.com/u/Jenaroph)\ **Post date:** [August 25, 2010, 12:32am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/52 "2010-08-25T00:32:55Z")
> [@Raygun99](#): > > > [@Jenaroph](#): > > > > “Tootie.” > > “I just like saying that name.” Yay! 😃 ---
**Author:** ![qazwart](https://avatars.discourse-cdn.com/v4/letter/q/5fc32e/32.png) [@qazwart](https://boards.straightdope.com/u/qazwart)\ **Post date:** [August 25, 2010, 1:10am UTC](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114/53 "2010-08-25T01:10:31Z")
Thermoses simply prevent heat transfer whether into the thermos or out of the thermos. You put something cold in, it’ll stay cold because heat cannot enter the thermos. If you put in something hot, it stays hot because the heat cannot get out. There was once a story of a man who claimed that thermoses never worked for him. He’d make himself a martini for lunch at night, put it in a thermos, and put it in the fridge. When he had it for lunch, it was warm. Of course, the joke is that the martini never got cold because the thermos kept the warmer martini from passing the heat into the fridge. P.S. Tell your friend that the light does go out when you close the refrigerator door. [Previous page](https://boards.straightdope.com/t/how-do-thermoses-know-if-they-are-supposed-to-keep-drinks-hot-or-cold/551114.md?page=2)