Atmospheric Pressure
The weight of air above us produces pressure of about 101 kPa.
About this topic
The weight of the air above us produces atmospheric pressure of about 101 kPa (1 atm) at sea level, around 10 tonnes per square metre. We don't feel it because the fluids inside our bodies push back equally.
Pressure falls with altitude as there is less air above: at the top of Everest it is about one third of sea-level pressure, so climbers need oxygen. Torricelli's mercury barometer shows the pressure as a column about 760 mm high, because the air's pressure balances the weight of the mercury. A water barometer would need to be about 10.3 m tall.
Worked example: a flat sheet of area 1 m² has about 101,000 N, the weight of ten tonnes, pressing on it. The Magdeburg hemispheres demonstration in 1654 showed two teams of horses couldn't pull apart two evacuated metal halves. Drinking through a straw works because your mouth lowers the pressure and the atmosphere pushes the drink up.
Weather maps use pressure: low pressure usually brings clouds and storms, high pressure brings clearer skies. Altimeters in aircraft estimate height from pressure, and pressure cookers raise the boiling point of water. A misconception is that suction pulls; in fact it is the surrounding atmosphere that pushes.
Key ideas
- Falls with altitude
- Barometers measure it
- Straws and suction rely on it
Quick check
Use cases: where Atmospheric Pressure helps
- Homework: review the key idea behind Atmospheric Pressure before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Atmospheric Pressure without notes.
- Visual learning: play with the interactive lab to see how Atmospheric Pressure changes when you adjust its inputs.
- Teaching a friend: explain Atmospheric Pressure in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Atmospheric Pressure?
The weight of air above us produces pressure of about 101 kPa.
What will I learn in Atmospheric Pressure?
Falls with altitude. Barometers measure it. Straws and suction rely on it.
Is Atmospheric Pressure part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Atmospheric Pressure lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Atmospheric Pressure?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.