Atmospheric pressure is the weight of air pressing down on Earth’s surface. It’s the reason you don’t float away and why your ears pop on airplanes. This invisible force shapes our world in ways we often don’t notice.
The Standard Atmosphere: A Unit of Measurement
Scientists use a unit called the standard atmosphere (atm) to measure air pressure. One atm equals 101,325 pascals, which is roughly the average pressure at sea level. This gives us a baseline to compare pressures across different locations and altitudes.
Pressure Changes with Altitude
As you climb a mountain, you’ll notice the air getting thinner. That’s because there’s less air above you pushing down. For every 100 meters you climb, the pressure drops by about 1.2 kilopascals. This is why climbers need special gear at high altitudes – the low pressure makes it harder to breathe.
The Barometric Formula: Pressure in Numbers
Scientists use a fancy equation called the barometric formula to calculate pressure at different heights:
p=p0⋅(1−L⋅hT0)g⋅MR0⋅Lp=p0⋅(1−T0L⋅h)R0⋅Lg⋅M
Don’t worry if that looks like alphabet soup. The important thing is that it helps meteorologists and engineers predict how pressure changes with altitude.
Pressure Variations: Nature’s Weather Engine
Atmospheric pressure isn’t constant. It changes from place to place and over time. These variations drive our weather patterns. High-pressure areas usually bring clear skies, while low-pressure zones often mean clouds and rain.
Record-Breaking Pressures
The highest sea-level pressure ever recorded was 1,084.8 hPa in Mongolia. That’s like having an extra 8% of air pressing down on you. On the flip side, the lowest pressure (outside of tornadoes) was 870 hPa during Typhoon Tip in 1979. That’s a difference you could literally feel.
Pressure in Everyday Life
You might not think about air pressure much, but it affects you every day:
- It’s why your ears pop in elevators or on planes
- It determines how high water can be pumped using suction
- It changes the boiling point of water, affecting cooking at high altitudes
Next time you check the weather forecast, remember – you’re looking at a map of this invisible force that shapes our world.
Citations:
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.
In most circumstances, atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so atmospheric pressure decreases with increasing elevation. Because the atmosphere is thin relative to the Earth's radius—especially the dense atmospheric layer at low altitudes—the Earth's gravitational acceleration as a function of altitude can be approximated as constant and contributes little to this fall-off. Pressure measures force per unit area, with SI units of pascals (1 pascal = 1 newton per square metre, 1 N/m2). On average, a column of air with a cross-sectional area of 1 square centimetre (cm2), measured from the mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons, resulting in a pressure of 10.1 N/cm2 or 101 kN/m2 (101 kilopascals, kPa). A column of air with a cross-sectional area of 1 in2 would have a weight of about 14.7 lbf, resulting in a pressure of 14.7 lbf/in2.
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atmospheric pressure (countable and uncountable, plural
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