# Atmospheric Pressure Definition and Explanation
## What is Atmospheric Pressure?
Atmospheric pressure, also known as barometric pressure, is the force exerted by the weight of the Earth’s atmosphere on a given surface area. It’s essentially the weight of the air above us pressing down on everything at the Earth’s surface.
The standard unit for measuring atmospheric pressure is the pascal (Pa), though other units like atmospheres (atm), millimeters of mercury (mmHg), and pounds per square inch (psi) are also commonly used.
## How Atmospheric Pressure Works
Atmospheric pressure results from gravity pulling air molecules toward the Earth’s surface. The air molecules, while individually light, collectively create significant pressure because there are so many of them in the atmosphere.
Key characteristics of atmospheric pressure include:
– Decreases with altitude – there’s less air above you at higher elevations
– Varies with weather conditions
– Changes with temperature (warm air is less dense than cold air)
– Affected by Earth’s rotation and geography
## Measuring Atmospheric Pressure
Scientists use barometers to measure atmospheric pressure. There are two main types:
### Mercury Barometer
Invented by Evangelista Torricelli in 1643, this device uses a column of mercury in a glass tube. The height of the mercury column changes with atmospheric pressure.
### Aneroid Barometer
This more modern device uses a small, flexible metal box called an aneroid cell that expands or contracts with pressure changes.
## Standard Atmospheric Pressure
At sea level and at a temperature of 15°C (59°F), standard atmospheric pressure is defined as:
– 101,325 pascals (Pa)
– 1 atmosphere (atm)
– 760 millimeters of mercury (mmHg)
– 29.92 inches of mercury (inHg)
– 14.7 pounds per square inch (psi)
## Importance of Atmospheric Pressure
Atmospheric pressure plays crucial roles in:
– Weather patterns and forecasting
– Aviation (altitude measurements)
– Human physiology (especially at high altitudes)
– Industrial processes
– Cooking (pressure cookers use increased pressure)
– Scientific research
Understanding atmospheric pressure helps meteorologists predict weather changes, as areas of high and low pressure are associated with different weather conditions. It’s also essential for pilots, mountaineers, and anyone working in environments where pressure varies significantly from sea level conditions.
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