Atmospheric pressure is the force per unit area exerted by the weight of the Earth's atmosphere on the surface of the Earth or any other object placed within it.
This is because the Earth's atmosphere is pulled towards the center of the Earth due to gravity. As a result, the weight of the atmosphere exerts a force in the downward direction.
Atmospheric pressure is commonly measured using a barometer, which measures the height of a column of mercury or other liquid that is supported by the air pressure.
The most commonly used units to measure atmospheric pressure are pounds per square inch (psi), millibars (mb), and pascals (Pa). Other units such as atmospheres (atm) and inches of mercury (inHg) are also used in certain contexts.
Yes, atmospheric pressure decreases as altitude increases. This is because there is less atmosphere above an object at higher altitudes, resulting in less weight and therefore less pressure exerted on the object.