Atmospheric Pressure
Barometer at different altitudes. Builds on Hydrostatic Pressure & Pascal.
You fill a glass to the brim with water, place a thin card on top, then flip the whole thing upside-down. You're holding the card in place with your hand.
What happens when you let go of the card?
The card stays put and the water defies gravity! The atmosphere pushes up on the card with about 101,325 Pascals of pressure — that's over 10 tonnes per square meter. A glass of water weighs only a few hundred grams. The atmospheric pressure wins by a landslide.
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Watch the force arrows — the blue atmospheric pressure arrows push UP while the red gravity arrow pulls DOWN. Adjust the water level to see when the atmosphere can (and can't) hold the water.
P_atm ≈ 101,325 Pa
One atmosphere of pressure is equivalent to a 10-meter column of water — far more than any drinking glass can hold.
Your diaphragm creates slightly lower pressure in your lungs — the atmosphere pushes air IN for you.
You don't 'suck' liquid up — you lower the pressure inside the straw, and the atmosphere pushes the liquid up.
At high altitude, less atmosphere above means less pressure, which means less oxygen pushed into your lungs.
In 1654, two hollow copper hemispheres with vacuum inside couldn't be pulled apart by 16 horses — atmospheric pressure held them together.
“You're swimming in an invisible ocean of air right now. It's crushing you with 10 tonnes per square meter — and you don't even notice.”
Journey to the Edge
Travel from the deepest ocean trench to the edge of space. Watch how pressure changes as you rise through Earth's atmosphere — and discover the surprising places where pressure matters most.
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Start at the Mariana Trench and slowly rise. Watch the pressure gauge plummet as you ascend. Notice how most of the atmosphere is concentrated in the lowest few kilometers. At airplane cruising altitude (10km), you've already left 75% of the atmosphere below you!
Atmospheric pressure decreases exponentially with altitude. Half the atmosphere is below 5.5 km. At the top of Everest, pressure is only 1/3 of sea level. In space, it drops to zero. This is why pressurized cabins and spacesuits exist.