What does atmospheric pressure measure?

Atmospheric pressure specifically refers to the weight of the atmosphere pressing down on the Earth's surface. It is the force that is exerted by the weight of air molecules in the atmosphere as they are pulled towards the Earth by gravity. This pressure decreases with altitude because there is less air above to exert force as one moves higher into the atmosphere.

Understanding atmospheric pressure is crucial in various fields, including meteorology, aviation, and fluid dynamics, as it influences weather patterns, aircraft performance, and the behavior of fluids. The measurement of atmospheric pressure is commonly done using barometers, and it is expressed in units such as pascals or millibars.

While the other options involve different types of pressure or forces, they do not capture the essence of atmospheric pressure, which is fundamentally about the weight of the air in the atmosphere acting on a given area at the Earth's surface.