COMMON TYPES OF WORK 177 



188. A problem in work. If a primitive man wishes to 

 remove his dugout canoe from the water, he knows no way 

 to do so but to lift it or drag it out. If it is too heavy for 

 this he may call in his neighbors and thus secure enough 

 men to do the work. If there are no neighbors the work 

 cannot be done. 



Intelligent men have learned ways of helping themselves 

 which enable them to overcome obstacles of this sort. Let 



FIG. 90. The use of pulleys 



By the use of pulleys, rope, and wheels one man may move a much greater weight 

 than he could by pulling directly upon the object 



us suppose that a boy has a boat weighing two thousand 

 pounds and that he wishes to pull it out of the water. It 

 is not necessary for him to call in his fellows if he under- 

 stands the use of simple machines. There are several sets 

 of appliances which might serve his purpose, but let us sup- 

 pose that he has at hand some boards, rollers, rope, and two 

 pulley blocks each of which contains two pulleys. 



The boy could lay boards on the beach, with the rollers 

 ready to support the boat, attach one pulley block to the 

 boat and the other to a tree or post, and thread the rope 

 through the pulleys as represented in figure 90. The boat 

 could then be moved along the boards by pulling on the rope. 



