Atmospheric air pressure, often simply referred to as air pressure, is the force exerted per unit area by the weight of the atmosphere above a given point on the Earth’s surface or within the atmosphere itself. It is caused by the gravitational attraction of the Earth on the air molecules composing the atmosphere. As altitude increases, atmospheric pressure generally decreases since there is less air above exerting force downward. Atmospheric pressure is typically measured using instruments such as barometers and is commonly expressed in units of Pascals (Pa), millibars (mb), or inches of mercury (inHg).
Where:
- is the atmospheric pressure in (N/m²),
- is the density of air in (kg/m³),
- is the acceleration due to gravity in (m/s2), and
- is the height (altitude) above sea level in (Km).
The SI unit for atmospheric pressure is the Pascal (Pa), where 1 Pascal is equivalent to 1 Newton per square meter (N/m²).