David queen, age 14, of brevard, n.c., for his quest on:
How does a vacuum bottle keep things cold?
The word vacuum is coined froze a latin word meaning empty. But the astrophysicists suspect that there is no such thing as totally empty space in the entire uriiverse. There are a few specks of matter in the most deserted regioris of space. And science has failed to produce a perfect vacuum.
When we speak of a vacuum, we mean a space empty even of air. But since we cannot rmove all the m01ecuies of gas from a container, we can create only a partial vacuum. You might suppose that an empty space can do nothing at all. But like everything else, a vacuum has its own qualities. It is a barrier to light and sound. In a vacuum bottle, all but about a thousandth part of the air has been removed. This partial vacuum can keep things cold or hot for about 24 hours.
A vacuum bottle is made to slow down the transfer of heat from the inside to the outside of the flask. And heat is transferred by three methods. A moving gas or liquid carries and spreads its heat from place to place by convection. The core of the vacuum bottle is built to slow down this heat transference by convection.
If you take the bottle apart, you see that the inside is a silvery glass flask. Actually it is two flasks, one inside the other. The air, or most of it, has been removed from the thin space between them to create the partial vacuum, and the rims are sealed together. The transference of heat convection is slowed down, because air cannot pass through this thin wall of nothingness.
Heat also travels by conduction. When one end of a poker gets hot, the heat is transferred from one m01ecuie to the next until. The poker gets warmed from end to end.. The sealed vacuum in the bottle reduces heat by conduction, because it is not easy for the sparsely scattered molecules of gas to transfer heat frown one to another.
Heat also travels by radiation, as the sun's radiant heat traveis across space. The silvery vacuum flask cuts down radiation just as a cloud blocks the sun's heat from reaching the ground. Some substances conduct heat more readily than others. Glass, cork and certain plastics are poor heat conductors which is why we use them to make the wells and the stopper which seals the vacuwn bottle.
The almost empty space of a vacuum bottle is tightly sealed, and it works to slow dawn the transference of heat between the inside and. The outside of the bottle. In a vacuum cleaner, a fan creates an unsealed pocket in the air. This near vacuum pulls in the surrounding air with enough force to drag along dust and dirt and other scraps of household debris.