50 Common Science 



clear across the ocean. No machinery needs oiling, 

 The clothes on your body feel smoother and softer than 

 the finest silk. Perpetual motion is an established fact 

 instead of an absolute impossibility ; everything that 

 is not going against gravity will keep right on moving 

 forever or until it bumps into something else. 



But, if there is no friction and you want to stop, you 

 cannot. Suppose you are in an automobile when all 

 friction stops. You speed along helplessly in the 

 direction you are going. You cannot steer the machine 

 your hands would slip right around on the steering 

 wheel, and even if you turn it by grasping the spoke, 

 your machine still skids straight forward. If you start 

 to go up a hill, you slow down, stop, and then before 

 you can get out of the machine you start backward 

 down the hill again and keep on going backward until 

 you smash into something. 



A person on foot does not fare much better. If 

 he is walking at the time friction ceases, the ground is 

 suddenly so slippery that he falls down and slides along 

 on his back or stomach in the same direction he was 

 walking, until he bumps into something big or starts 

 to slip up a slope. If he reaches a slope, he, like the 

 automobile, stops an instant a little way up, then starts 

 sliding helplessly backward. 



Another man is standing still when the friction is 

 turned off. He cannot get anywhere. As soon as he 

 starts to walk forward, his feet slip out from under 

 him and he falls on his face. He lies in the same spot 

 no matter how he wriggles and squirms. If he tries to 

 push with his hands, they slip over the rough ground 



