Atmospheric pressure

Atmospheric pressure is the force per unit area exerted by the atmosphere. It varies with altitude, weather, and location because air density and the mass of air above a point change.

Hydrostatic equilibrium: A condition in which pressure gradients balance the force of gravity within a fluid. The balance between gravity and vertical pressure gradients describes how atmospheric pressure changes with height.
Barometer: An instrument that measures atmospheric pressure. Barometers turn atmospheric pressure into a measurable quantity for weather and elevation work.
Pressure: The normal force exerted per unit area on a surface. Atmospheric pressure is one instance of this broader physical quantity.
Gauge pressure: Pressure measured relative to the surrounding atmospheric pressure. Many gauges omit atmospheric pressure, while absolute pressure includes it.
Barometric formula: An equation describing how atmospheric pressure varies with altitude under specified temperature and gravity conditions. It quantifies the pressure decrease that follows from the atmosphere’s vertical structure.
Weather forecasting: The use of observations and models to predict future atmospheric conditions. Pressure patterns help identify developing storms and fair-weather systems.
Pascal (unit): The SI unit of pressure, equal to one newton per square metre. It provides the standard unit for reporting atmospheric pressure in physics.
Absolute pressure: Pressure measured relative to a perfect vacuum. Atmospheric pressure is an absolute pressure when reported relative to vacuum.
Ideal gas law: A relation among a gas’s pressure, volume, temperature, and amount of substance. Together with air temperature and density, it links pressure to the atmosphere’s physical state.
Altimeter: An instrument that estimates altitude, often by measuring atmospheric pressure. Because pressure generally falls with height, pressure-based altimeters estimate elevation.

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