COMMON TYPES OF WORK 175 



of water power and of other sources of energy in order to 

 accomplish the needful work of the world. Buildings must 

 be constructed, trains moved across the country, steamships 

 driven across the ocean. Land must be plowed, crops planted, 

 ditches dug, the floors scrubbed, the lawns mowed. Work 

 must be done every day in every inhabited part of the world. 

 If the land were not plowed and planted and the crops har- 

 vested, there would be little for us to eat. If the trains and 

 ships did not carry food for our great cities, many of us would 

 starve to death, as has happened in countries like India, where 

 transportation facilities are not equal to the task of properly 

 distributing the food that is produced in the country. 



It is not possible for us to accomplish all these tasks by 

 our unaided strength, and we must therefore use various 

 machines to assist us or to utilize the forces of nature. One 

 of the great differences between savage and civilized men 

 lies in the ability of the latter to help themselves in getting 

 this work done. In this chapter we shall study about work 

 and the means of accomplishing it. 



187. Different methods of working. The first men doubt- 

 less did everything with their unaided hands, but soon they 

 learned that a heavy object could be pried up with a stick 

 more easily than it could be lifted by the hands, that a sling 

 would throw a stone harder than the unaided hand, that a 

 log could be rolled up an incline if it was too heavy to be 

 lifted, and that an arrangement of rope and pulleys would 

 make it possible to hoist very heavy weights by the use of 

 small force. Gradually the more intelligent part of mankind 

 has developed the use of simple machines and combinations 

 of them, until now there is scarcely any work done without 

 the use of some sort of mechanical contrivance. The sim- 

 ple machines, which are the basis of the devices which we 

 employ to assist us in working, are the lever (fig. 89), the 

 pulley, the inclined plane, the wheel and axle, the screw, 

 and the wedge. 



