How do thermoses know if they are supposed to keep drinks hot or cold?

my friend wants to know

They don’t. They prevent the radiation or convection of heat, in or out.

There’s millions of tiny elves that keep the hot molecules and the cold molecules where they belong.

They aren’t elves, they are demons. Maxwell’s demons.

They have the silver hammers and they cause headaches.

Max Planck?
Coffee thermoses work from quantum mechanics?

Your friend hasn’t been telling a certain joke, now, has he? One about the greatest invention in the world?

No, James Clerk Maxwell, probably the third or fourth greatest physicist in history. He’s most famous for completing the classical understanding of electromagnetism, but he also did a lot of important work in thermodynamics.

In all seriousness, all a thermos does is it keeps what’s inside of it from exchanging heat with its environment, and thereby in practice keeps the contents at the same temperature they were at when they were put in. If you boil lemonade and put it in one thermos, and freeze coffee and put it in another, the lemonade will stay hot and the coffee will stay cold, even though they’re “supposed” to be the other way around.

Put it another way: A wall can either keep people inside, or keep them outside. How does it know which to do? It doesn’t; it just keeps people on the same side they start on. A thermos is like a wall, but one that blocks heat, not people.

Is your friend about to ask us why we park on a driveway and drive on a parkway? That makes me feel something ending in -gry, but not angry or hungry.

They don’t know. A thermos is pretty stupid so you have to tell it what to do with the contents, like, “keep this soup hot thermos.” I take advantage of this by filling mine with water and telling it, “keep this Czech style wheat beer ice cold thermos.” Delicious.

It’s like a McDLT box. It keeps the hot side hot and the cold side cold.

In the McDLT commercial the cheese is on the cold side. Shouldn’t it be on the hot side so it melts onto the meat?

Do they still sell those things?

wizard named Dewar did it, caused all thermos bottles to behave like that forever.

If you were to consider him the fourth, whom would you consider the third?


Yeah, one time I totally screwed up and forgot to tell my Thermos to activate hot mode, so when I went to drink my hot chocolate, I ended up with cold chocolate! It ruined my day.

Newton and Einstein are the top two, then maybe Archimedes, then Maxwell.

In the world PSXer and his friend seem to live in? Probably.

Yes. That’s why McDLT’s are disgusting.