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.
You can read more about air pressure at this website
Thanks for your question!
(republished on 08/02/06)