How does a thermos keep things both hot and cold?!
How does a thermos keep things both hot and cold?
Answers:
One way to build a thermos-like container would be to take a jar and wrap it in, for example, foam insulation. Insulation works by two principles. First, the plastic in the foam is not a very good heat conductor. Second, the air trapped in the foam is an even worse heat conductor. So conduction has been reduced. Because the air is broken into tiny bubbles, the other thing foam insulation does is largely eliminate convection inside the foam. Heat transfer through foam is therefore pretty small.
Source(s):
http://home.howstuffworks.com/thermos2.h...
magic
There are two layers of glass. There is a vacuum between the layers. Since there is no air to transfer the heat/cold to the outside it will keep it's temperature longer. I think they used to call them 'vacuum jugs'. Thermos is a brand name.
Agree with tumbleweed, except that there is not always glass inside a thermos. It can be any material - usually metal these days. The vacuum space between the layers of material is what keeps the temperature from rising or dropping.
Insulation
There are two layers, between them there is a vacuum. So the liquid in the thermos is isolated from the external system so it keeps its energetic status.