Molecular Attraction 51 



more easily than they now slip through air. He cannot 

 push sideways enough even to turn over. If there 

 happens to be a rope within reach and one end is tied 

 to a tree, he might try to take hold of the rope to pull 

 himself along. But no matter how tightly he squeezes, 

 the rope slips right through his hands when he starts 

 to pull. If, however, there is a loop in the rope, he can 

 slip his hand through the loop and try to pull. But 

 the knots with which the rope is tied immediately come 

 untied and he is as helpless as ever. 



Even if he takes hold of a board fence he is no more 

 successful. The nails in the board slip out of their 

 holes and he is left with a perfectly slippery and useless 

 board on the ground beside him for a companion. As 

 it grows cold toward evening he may take some matches 

 out of his pocket and try to start a fire. Aside from the 

 difficulty of his being unable to hold them except by 

 the most careful balancing or by shutting them up within 

 his slippery hands, he is entirely incapable of lighting 

 them ; they slip over the cement beneath him or over 

 the sole of his shoe without the least rubbing. 



In the real world, however, it is fortunately as impos- 

 sible to get away from friction as it is to get away from the 

 other laws we have tried to imagine as being turned 

 off. There is always some friction, or rubbing, when- 

 ever anything moves. A bird rubs against the air, 

 the point of a spinning top rubs against the sidewalk 

 on which it is spinning. Your shoes rub against the 

 ground as you walk and so make it possible for you to 

 push yourself forward. The drive wheels of machinery 

 rub against the belts and pull them along. There is 



