II 



HOW WORK IS DONE 



THE word energy implies capacity to do work. 

 Work, considered in the abstract, consists in 

 the moving of particles of matter against some 

 opposing force, or in aid of previously acting forces. In 

 the last analysis, all energy manifests itself either as a 

 push or as a pull. But there is a modification of push 

 and pull which is familiar to everyone in practice under 

 the name of prying. Illustrations may be seen on every 

 hand, as when a workman pries up a stone, or when a 

 housewife pries up a tack with the aid of a hammer. 

 The principle here involved is that of the lever a princi- 

 ple which in its various practical modifications is every- 

 where utilized in mechanics. Very seldom indeed is 

 the direct push or pull utilized; since the modified 

 push or pull, as represented by the lever in its various 

 modifications of pulley, ratchet-wheel, and the like, 

 has long been known to meet the needs of practical 

 mechanics. 



The very earliest primitive man who came to use any 

 implement whatever, though it were only a broken 

 stick, must have discovered the essential principle 

 of the lever, though it is hardly necessary to add that he 

 did not know his discovery by any such high-sounding 



[39] 



