Vacuum Doesn’t Always Mean “No Air”
What does vacuum mean?
It’s easy to think that vacuum means “no air,” but it’s actually a bit wrong.
For example, typical vacuum-packed foods contain a great deal of air.
However, the expression “vacuum packing” is not wrong.
Vacuum means “a space filled with gas at a lower atmospheric pressure than usual”.
You don’t have to completely evacuate the air to create a vacuum.
In other words, any place where the air is thinner than the space we usually live in maybe called a vacuum.
Vacuum is divided into three stages, high vacuum, medium vacuum, and low vacuum, in order from the one with the strongest atmospheric pressure.