Air pressure refers to the weight of the Earth's atmosphere pressing down on surfaces. The average air pressure at sea level is 101.325 kPa or 14.696 lbs/sq2. We can survive this pressure because our bodies evolved in this environment. Variations in air pressure cause weather phenomena like storms and hurricanes. Pressure also seeks to equalize, as seen in high-pressure machinery needing structural integrity and the difficulty of sustaining a vacuum.