Why Does the Atmosphere Exert Pressure?
Everything around you is made up of tiny particles called molecules. This includes even your own body. In a solid object such as a rock, these molecules are bound to each other tightly, not moving very much. This allows a solid to keep its shape. A liquid, such as water, is also made up of molecules, but these molecules are much less forcefully bound to one another. They still remain together, but are free to move around somewhat. The molecules making up a gas, such as the gases in our atmosphere, are not bound to each other at all. They are free to move about, bumping into each other as well as into liquids and solids.
As the molecules of the atmosphere move around, bumping into objects such as your body, they create a pressure. This pressure is omnidirectional, meaning that it is not only exerted from above, but also from beneath, from the sides, and from every direction at once.
At sea level, the amount of pressure exerted by our atmosphere is about 14.7 pounds per square inch. This is around one kilogram per square centimeter. This means that at sea level an object will have 14.7 pounds of pressure pushing against every square inch of the object.
Yet, as we move around in the atmosphere, we are unaware of this pressure. We do not feel it because our bodies are made up of gases that are at the same pressure. In other words, the gases within our bodies actually push back outward at the same pressure.