Atmospheric Pressure:

The Earth is surrounded by a cover of air called the atmosphere. It extends to a few hundred kilometers above sea level. Just as certain sea creatures live at the bottom of the ocean, we live at the bottom of a huge ocean of air. Air is a mixture of gases. The density of air in the atmosphere is not uniform. It decreases continuously as we go up. Atmospheric pressure acts in all directions.

Experiment:

Take an empty tin can with a lid. Open its cap and put some water in it. Place it over the flame. Wait till the water begins to boil and the steam expels the air out of the can. Remove it from the flame. Close the can firmly by its cap. Now place the can under tap water. The can will squeeze due to atmospheric pressure.

When the can is cooled by tap water, the steam in it condenses. As the steam changes into water, it leaves a space behind it. This lowers the pressure inside the can as compared to the atmospheric pressure outside the can. This will cause the can to collapse from all directions. This experiment shows that the atmosphere exerts pressure in all directions.

The fact can also be demonstrated by collapsing of an empty plastic bottle when air is sucked out of it.