What's in a vacuum



Anja: You may have to imagine it as something empty and at the same time completely `` clean '', because any contamination would mean that there is still some substance in it. Therefore it has to be a closed space, into which nothing can penetrate from outside. Otherwise an already existing vacuum will not be maintained.

Sara: So there is a vacuum in a container that comes out of the dishwasher with a lid on it. Of course you have to make sure that there is no more speck of dust in it.

Anja: You are already on the right path, but you have forgotten that besides your visible dust grains there are also very much smaller particles that you cannot see, but which still disrupt the vacuum. Think, for example, of the particles that make up our air: you cannot see or feel them either, but they are still there.

Anja: That is exactly the point: empty means that it no longer contains any gas, such as air. It is often colloquially referred to as a vacuum. However, it must not contain any other gaseous substance. The consequence of this is that the pressure in this glass is very small, since there are no longer any particles in it that exert a force on a surface through their impact against the walls. This is how the pressure is defined: