186 SIMPLE MACHINES 



have come into such general use in pumping water for the 

 uses of the farm. The windmill relieves the farmer and 

 his family from the drudgery of pumping water, and 

 leaves them free for other labor. The windmill, like the 

 sailboat, kite, and aeroplane, works upon the principle 

 that if wind strikes a plane obliquely, part of the force of 



the wind is exerted in producing 

 forward (or upward) motion. 

 In the windmill the planes (sails) 

 are attached to a hub (Fig. 191) ; 

 as the planes move forward, the 

 hub, or wheel, revolves. The 

 " pin-wheel " we used when 

 children is a miniature windmill. 



For the pumping of water, the re- 

 volving wheel is attached to a piston 

 A Dutch windmill. Copyright The which moves up and down in a pump 

 cat t ur?iin n n ot StereographCo> ' **" fcf- 42); water is thus raised out of a 



well or cistern. On windy days the 



windmill pumps the water into a raised tank, from which it can be 

 drawn when there is no wind, and the mill is quiet. 



A recent article states that a village in Alaska, far within the Arctic 

 Circle, is to have its long night, of six months, illuminated by electri- 

 city. The average wind velocity at the village is 20 miles an hour, and 

 a large windmill will operate the dynamo that gives the current for the 

 light (c/. 162). 



211. Summary. The complicated machines used by man are forms 

 of six simple machines: the lever, pulley, wheel and axle, inclined 

 plane, wedge, and screw. 



A machine enables man to exert force more advantageously, but it 

 does not create any energy. 



Power x distance power moves equals weight x distance weight 

 moves. 



