Physics
Air pressure & weather
An invisible ocean of air presses on you. It explains suction cups, straws and the weather.
What you need first
You drink through a straw, press a suction cup onto the tiles, or hear about a in the weather . Behind all of it is the same invisible force: the pressure of the air. We live at the bottom of a huge ocean of air, many kilometres deep, and all that weight presses on us constantly.
Air has weight
Air feels like nothing, but it is made of countless particles, and they have mass. At , the whole column of air above you presses with about 1 bar, which is roughly the weight of 1 kg on every single square centimetre. The palm of your hand is about 80 square centimetres, so roughly the weight of an adult, around 80 kg, rests on it! You do not feel it because the air presses equally from all sides, including from below and from inside your body. Pressure is always force divided by area: the same force on a smaller area gives a higher pressure.
Same force, small area: high pressure.
Suction cup and straw: pressure differences at work
A suction cup does not actually suck at all. When you press it on, you push the air out from underneath it. There is then almost no air inside, but the full air pressure still pushes from outside: the outside air presses the cup against the tile. A straw works the same way: you suck the air out of the straw, and the air pressure pushing down on your drink pushes the lemonade up into your mouth. Without a pressure difference nothing happens: the side with the higher pressure always wins.
Highs, lows and thin mountain air
Air pressure is not the same everywhere. Where air sinks, a forms: usually calm, sunny weather. Where air rises, a low pressure area forms: the rising air cools, and clouds and rain develop. Meteorologists measure pressure in hectopascals, where 1 bar is exactly 1000 hPa: at sea level around 1013 hPa is normal. And the higher you climb, the less air remains above you: on a mountain the air is thinner and the pressure lower. That is exactly why your ears pop in a plane or a cable car, when the pressure inside and outside has to even out again.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
Roughly how big is the air pressure at sea level?
Why does a suction cup stick to a smooth tile?
A high has 1030 hPa, a low has 990 hPa. How big is the pressure difference in hPa?
Match each term with the description that fits.
In the valley you measure 1000 hPa, on the mountain top 700 hPa. By how many hPa is the pressure lower up there?
At sea level the normal air pressure is about … hPa.
Where this leads