AtmosphericPressure

Atmospheric pressure is the force exerted by the Earth's atmosphere on matter. It arises from the weight of the air above a point and is described by the hydrostatic balance of the atmosphere. The pressure at a location decreases with altitude and varies with weather conditions.

Pressure is measured in several units, most commonly pascals (Pa), kilopascals (kPa), and atmospheres (atm). Other common units include millimeters of mercury (mmHg, also called torr) and pounds per square inch (psi). The standard atmospheric pressure at sea level is defined as 1 atm, equal to 101,325 Pa or 1013.25 hPa, and 760 mmHg. Weather systems cause pressure to vary around sea level, typically from about 970 to 1050 hPa.

Mercury barometers and aneroid barometers are used to measure atmospheric pressure. In meteorology, pressure readings help forecast weather, while aviation and mountaineering rely on pressure data for altitude information and safety.

With increasing altitude, pressure falls roughly exponentially. In the International Standard Atmosphere, sea-level pressure is 1013.25 hPa, dropping to about 89 kPa at 1,000 meters and around 54 kPa at 5,000 meters. Temperature and humidity influence the exact profile.

Practical relevance includes weather prediction, aviation and scuba diving. In aircraft, cabin pressure is regulated to about the equivalent of 6,000 to 8,000 feet above sea level, extending safety and comfort.