What exactly is a vacuum?
When you buy a vacuum flask or a vacuum cleaner, you are really paying money for what would seem to be nothing at all, Your money, howevery is well spent, for this nothing can do all kinds of work. The flask can keep hot soup hot or cold drinks cold for hours. The vacuum cleaner can pick up the dirt and draw out the dust as if by magic.
The world seems to be full of large and small empty spaces, but this is not so. An empty drawer is full of air. Air fills the wide outdoors and seeps down into the small pockets of the crumbly soil. If you remove a small pocket from the air, the surrounding air rushes in to fill up the hole, ,just as water flows in to fill up a hole.
It is no easy job to remove the air from a seemingly empty space, 1rihen you perform this trick, you have a vacuum a hole full of nothing. Your vacuum must be sealed at once or air and maybe many other things will rash in to fill it up again.
The vacuum in a vacuum flask is sealed between a double wall of glass. The vacuum of a vacuum cleaner is made and remade so long as the motor runs. The motor drives a fan which draws our a column of air and air from the room flows in through the nozzle to replace it, to fill up the holes The rush of replacing air is so strong that it draws dust and debris along with it.
If you put an alarm clock into a glass jar, remove the air and seal the jar, you will discover that a vacuum has still other qualities, The clock will go on ticking, the alarm bell will ring, but you will be unable to hear a sound. For sound cannot pass through the empty space which is a vacuum. Heat cannot pass through a vacuum either, This is why a vacuum flask can keep soup hot.
It keeps a cold drink cold because it also refuses to let heat pass from the outside to the inside of the flask.
The empty space which is a vacuum, then, is far from nothing. It can be very useful and we have put it to work in many other gadgets besides flasks and cleaners. However, the best man made vacuum can be called only a partial vacuum. A few molecules of air remain in a vacuum tube and also between the glass walls of the flask. If we could make a perfect vacuum, free from the last molecule of air, and then seal it, we would have a pocket of complete silence with a temperature that never changed..
You put a small vacuum to work when you suck a soda pop through a straw. As you suck on the straw, you draw out some of the air. This removes the normal air pressure from the sods, and the liquid rushes all by itself up into your mouth. A tornado is a large vacuum cleaner in action. For the center of this violent storm is an almost vacuum, pulling in the surrounding air with enough force to move a building.