# Q & A: Air pressure

Q:
I`m doing a science project that will go to the state science(hopefully) i think you this is too. Maybe not, but I need to get some info about AIR PRESSURE but i couldn`t find any in anywhere in internet so i you do have any info CAN I GET IT?
- terry (age 14)
IL hoffman estates US
A:

Hi Terry,

I have a question for you: do you think that air has weight?
It seems like a silly question; after all, you are able to move and walk around without feeling the air push on you, right? However, the correct answer to the question is yes, air does in fact weigh something! This was proven in 1655 by a man named Otto von Guericke in the town of Magdeburg. Von Guericke invented a pump that was able to remove the air from an enclosed space. He then made two bronze hemispheres about 50 cm in diameter that fit together to make an air-tight sphere, and proceeded to remove all the air from the inside of this sphere.

To everyone’s surprise, not only did the hemispheres remain stuck together after the air was removed, but it took 2 teams of 8 horses pulling in opposite directions to separate them! So let’s take a look at what happened here. Air was removed from the inside of the hemispheres, so the only thing that could have been holding the hemispheres together was the air on the outside pushing in on them. The pushing of the air is called air pressure. Normal air pressure on earth is about 15 pounds per square inch. This means that for every square inch of space, there are 15 POUNDS of air pushing on it! You can imagine that is why it was so difficult for Von Guericke to separate his hemispheres after he had removed the air from the inside.

You might be wondering why, if there is so much air pressure, you don’t normally feel any of this. Like I said in the first question I asked, you can move and walk around without feeling anything pushing on you. This is because the air pushes in all directions -- there is some air pushing down on you, but there is also air that is pushing from the inside. That’s why you can move around without feeling like you have a ton of weight pushing down on you.