Understanding Gas Pressure and Atmospheric Pressure

1. Gas Pressure

• according to the Kinetic Theory Of Gases, molecules in a gas are always moving randomly and constantly colliding with the walls of its container.
• collisions of gas molecules with the walls of the container occur frequently, resulting in a change of momentum which exerts a force on the wall of the container.
• the force per unit area produced by collisions of gas molecules on the walls of the container is the gas pressure. 

2. Atmospheric Pressure

• it is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth.
• it can extend up to 1000 km above Earth's surface and has a total mass about 5 million billion tonnes.
• the air molecules near Earth's surface are subjected to compression that produces higher air pressure which supports the atmosphere and prevents it from collapsing.
• we do not normally feel the large atmospheric pressure because the blood pressure inside our bodies can balance the external pressure.