Gravitation n 



compressed air in the blood and all through the body. 

 If you were to lie down on the ground and have all the 

 air pumped out from under you, the air above would 

 crush you as flat as a pancake. You might as well let 

 a dozen big farm horses trample on you, or let a huge 

 elephant roll over you, as let the air press down on you 

 if there were no air underneath and inside your body to 

 resist the pressure from above. It is hard to believe that 

 the air and liquids in our bodies are pressing out with 

 a force great enough to resist this crushing weight of air. 

 But if you were suddenly to go up above the earth's 

 atmosphere, or if you were to stay down here and go 

 into a room from which the air were to be pumped all at 

 once, your body would explode like a torpedo. 



When you suck the air out of a bottle, the surrounding 

 air pressure forces the bottle against your tongue; if 

 the bottle is a small one, it will stick there. And the 

 pressure of the air and blood in your tongue will force 

 your tongue down into the neck of the bottle from 

 which part of the air has been taken. 



In the same way, when you force the air out of a 

 rubber suction cap, such as is used to fasten reading 

 lamps to the head of a bed, the air pressure outside 

 holds the suction cap tightly to the object against 

 which you first pressed it, making it stick there. 



We can easily experiment with air pressure because 

 we can get almost entirely rid of it in places and can 

 then watch what happens. A place from which the air 

 is practically all pumped out is called a vacuum. Here 

 are some interesting experiments that will show what 

 air pressure does : 



