Air is something can be felt, but cannot be seen or tested.
On the earth, it is everywhere. Air contains a lot of gases, the major
components being nitrogen and oxygen. Apart from the ordinary gases, air
contains rare gases like neon, helium, krypton. Since air contains gases, which
have mass and hence weight, it also has weight. This weight is felt by all
things on the surface of the earth. This is know as atmospheres pressure.
