Where do you get vacuum in the vacuum flask?

Answer 1

The flask works because there is a gap between the inner and outer walls of the flask. During the manufacturing process the air in the gap is extracted and the opening is sealed - creating a vacuum between the walls.

Heat transmits rapidly through air - but a lot less rapidly, in fact only very, very slowly, through a vacuum.

A vacuum flask not only keeps heat in, it also keeps it out. If you put iced water into a vacuum flask it will stay cold for a very long time.

Answer 2

the cheapest and easiest way I know is to put a few ml of water in a flask you can heat in a microwave or on a burner (burner has worked best for me), when the water turns to steam it forces most of the air out, then (HEY, IT'S HOT) remove from the heat source and stick a stopper in the top (with a valve thing in the stopper if you want to use the vacuum for something else). When the steam cools, it condenses and creates a fairly good vacuum. They are fairly difficult to store for any length of time because of leakage and hydrogen diffusion, but good equipment works very well for a short period of time. Other more expensive ways are Mercury vapor, a commercial vacuum pump, Bernoulli tubes,... but very money and labor intensive.
In concept it's pretty simple: a vacuum flask (or Dewar flask, or thermos bottle) is essentially two nested bottles with a vacuum between. The bottles are generally made of plastic, glass, or metal. If they're glass, it's pretty common to add an outer metal jacket as protection in case the glass breaks, as it may implode with considerable force.

Answer 3

stopper, plastic or metal case, support, double glass bottle, vacuum, silvering and air.

Answer 4

it keeps things hot and cold by when you turn it on you actuall using electricity so it turns hot hen cold

Answer 5

A vacuum flask is double walled (a bit like double glazing) the vacuum is between the walls.