Air pressure is 1.036 kilograms per square (14.7 lbs per square inch at higher altitudes the pressure is less). The air presses down on us and against us. Air pressure within your body balances the pressure outside of your body.

Air pressure is measured by a mercury barometer. Weather maps often show pressure this pressure in units of the mercury column height. The average reading is 29.2 inches of mercury equivalent to 760 millimeters.

Air is matter. It has mass and and takes up space. Air is made up of different gases: nitrogen, oxygen, carbon dioxide, water vapor, and other gases. Air molecules are in constant motion. They move, and when they come in contact they push and press on the surfaces they contact. Air pressure is caused by all of the air molecules in Earth's atmosphere pressing down on Earth's surfaces.