WORK AND MACHINES 163 



However, there is a difference, sometimes a great difference, between 

 the energy expended and the amount of useful work done. The ratio 

 of useful work done to the energy used in doing it constitutes the effi- 

 ciency of the machine employed. 



The terms work and energy are correlative. The use of one implies 

 the other. A distinction which may be made in use of the terms force 

 and energy is that while all changes in matter are the results of forces 

 acting, the term energy is to be employed only when it is desired to 

 emphasize the fact that a change due to any force involves motion in 

 a body or in its parts. Work has been done upon the body. 



While theories are only suppositions, they are always based upon 

 facts, and in their applications must always accord with the facts. 



For the transmission of energy from place to place some means or 

 medium is necessary. To account for the transmission of solar energy 

 through space destitute of all matter it is believed that an ether medium 

 exists. Only by supposing the existence of such a medium can the 

 transmission of light, heat, and other forms of energy outward through 

 space be accounted for. Assuming that it does exist makes possible 

 an understanding of phenomena otherwise inexplicable. 



Exercises 



1. What sharp distinctions are made in the use of the correlated terms force, 

 energy, and work? 



2. What is the literal meaning of the terms (a) transfer; (b) transform? 



3. In the realm of science does believing a thing so make it so? When only 

 does supposition become worthy of being entertained as a belief or an 

 opinion? 



4. Distinguish between theory and mere speculation. Of what service is 

 theory in the study of any science? 



5. What meaning has the statement that only in beliefs well-founded are 

 the great achievements of men wrought out? 



6. State the argument for the existence of an ether medium. 



LEVERS AND PULLEYS 



However simple or however complicated any device for 

 doing work may be it is called a machine. Through the 

 use of machines men employ to advantage their own strength 

 as muscular force, and what is of far greater importance 



