72 Common Science 



88. When you jump off a moving street car, you lean back. 



89. All water flows toward the oceans sooner or later. 



90. You can skate on ice, but not on a sidewalk, with ice skates. 



SECTION 12. Centrifugal force. 



Why does not the moon fall down to the earth? 



Why will a lasso go so far after it is whirled ? 



Why does a top stand on its point while it is spinning ? 



If centrifugal force suddenly stopped acting, you would 

 at first not notice any change. But if you happened 

 to get into an automobile and rode down a muddy street, 

 you would be delighted to find that the mud did not 

 fly up from the wheels as you sped along. And when 

 you went around a slippery corner, your automobile 

 would not skid in the least. 



If a dog came out of a pool of water and shook him- 

 self while centrifugal force was not acting, the water, 

 instead of flying off in every direction, would merely 

 drip down to the ground as if the dog were not shaking 

 himself at all. A cowboy would find that he could no 

 longer throw his lasso by whirling it around his head. 

 A boy trying to spin his top would discover that the top 

 would not stand on its point while spinning, any better 

 than when it was not spinning. 



These are little things, however. Most people would 

 be quite unconscious of any change for some time. 

 Then, as night came on and the full moon rose, it would 

 look as if it were growing larger and larger. It would 

 seem slowly to swell and swell until it filled the whole 

 sky. Then with a stupendous crash the moon would 

 collide with the earth. Every one would be instantly 

 killed. And it would be lucky for them that they 



