The atmosphere is the layer of gases surrounding a planet, held in place by gravity. Atmospheric pressure, on the other hand, is the force exerted by the weight of this atmospheric column on a unit area.
Understanding the Atmosphere
The atmosphere is a complex mixture of gases, primarily nitrogen and oxygen, extending hundreds of kilometers above the Earth's surface. Its composition and density vary with altitude. As noted in one source, "Atmosphere is basically the layer that surrounds a planet or any other material body. The atmosphere is held in place with the help of gravity of that body that is surrounded".
Defining Atmospheric Pressure
Atmospheric pressure is simply the pressure exerted by the weight of the air above a given point. It's measured in various units, such as Pascals (Pa), millibars (mb), or pounds per square inch (psi). As explained in a physics Stack Exchange response, "Atmospheric pressure is air pressure due solely to the weight of the air above you in the atmosphere." The pressure is not uniform; it decreases with increasing altitude because there is less air above. This is illustrated by NOAA's description of air pressure decreasing with height.
Key Differences Summarized:
| Feature | Atmosphere | Atmospheric Pressure |
|---|---|---|
| Definition | Gaseous layer surrounding a planet | Force exerted by the atmosphere per unit area |
| Nature | Physical entity (mixture of gases) | Physical quantity (force/area) |
| Variation | Composition and density change with altitude | Decreases with altitude |
| Measurement | Not directly measured as a single value | Measured using instruments like barometers |
Examples:
- A high-pressure system indicates a region with higher than average atmospheric pressure, while a low-pressure system has lower than average pressure. These differences drive wind patterns, as explained in the Center for Science Education resource on highs and lows of air pressure. Air moves from high to low pressure regions.
- Gauge pressure sensors, as discussed in a Reddit engineering thread, measure the difference between the pressure being measured and the atmospheric pressure.
