Figure 1-1 -- Earth s atmosphere.
Atmospheric Pressure and Temperature
The atmosphere is made up of molecules that we call air. These air molecules have
weight (approximately 1.2 ounces per cubic foot at sea level), and the amount of weight
these air molecules exert on the earth's surface is called atmospheric pressure. You
must understand how an aircraft uses atmospheric pressure to determine altitude and
how pressure and temperature changes affect the aircraft's instruments.