Eli5: Why can a thermal flask keep items cold for 24 hours, but only hot for 12 hours.
In: Physics
Randall Munroe’s answer on his What If? blog to “Would a toaster still work in a freezer?” is a good read, and has some relevant info: [https://what-if.xkcd.com/155/](https://what-if.xkcd.com/155/)
Me no sciency, but I’m guessing that the difference between room temp and 0 Celsius (frozen) is only like 20-25 degrees, where as boiling temp is 100 degrees (~75 degrees away from room temp).
Also, anything under room temp general feels ‘cold’ where as a few degrees under boiling things start to go from hot to ‘warm’ fast.
Hot objects with high thermal energy emit light. This is called radiation. The steel on the outside of a Yeti thermos catches this radiation and keeps it away from the cold stuff inside.
If the stuff on the inside is hot, however, IT is what emits light. It heats up the inner layer of the thermos, and that layer radiates heat away.
The way they’re designed, it’s much easier to keep heat out rather than in.
The difference between cold (0c) and not cold (25c) smaller than the different between hot (80c) and not hot (25c).
Which is why it’s harder to keep hot drinks hot compared to cold drinks cold.
TIL physicists have a particularly hard time at Eli5. Impossible to resist throwing in an equation or two
The science behind this is called thermodynamics.
When things have high energy they contain high heat which makes them hot. When they have low energy they are cold.
Energy like this always wants to flow from hot to cold. From high energy to low energy.
When something is already cold in the flask, for it to get warm, energy must flow from the flask into the cold item inside the flask. Flasks insulate from the outside so the heat flows very slowly in that direction.
When something is hot inside the flask, the energy flows must faster trying to leave the flask since the energy difference is greater.
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