Atmospheric Pressure Introduction

Our atmosphere is made up of an incredible number of molecules, bouncing around from place to place. One cubic inch of air near sea level has about 4.4x10²⁰ molecules in it! (That's around 440 billion billion molecules.) As these molecules move around, they are constantly colliding with each other or anything else that gets in the way - like us. The average force of all these collisions, per unit area that they hit, is called air pressure. Since the molecules move randomly in all directions, the air pressure at a given location is the same in every direction. At sea level, the weight of the air produces a force of about 14.7 pounds on every square inch of surface.