CONSERVATION OF ENERGY 



63 



mechanical energy, or when this mechanical energy is changed 

 by the dynamo into electrical energy. (Figure 23.) 



If you have ever bored a hole in hard wood, you have 

 noticed how hot the point of the drill becomes. A portion 

 of the energy you expended went to displace the particles 

 of wood, and a portion of your energy was transformed 

 by friction into heat. The portion of your energy which was 

 transformed into heat is usually referred to as lost energy, 

 because it did not help to accomplish the work you set out 



FIGURE 23. TRANSFORMATION OP ENERGY 



to do. Whenever man undertakes to change one form of 

 energy into another, there is always this " loss of energy." 



In a factory, for example, a great deal of the heat from 

 the burning fuel goes up the chimney and is also lost in 

 other ways. Even that part of the heat which is transformed 

 into mechanical energy cannot all be utilized. Much of it 

 is transformed back into heat by the friction of the moving 

 parts of the machinery. 



In reality, however, no energy is ever lost or destroyed. 

 It may be lost in the sense that it does not serve man's 

 immediate purpose, but it has not gone out of existence. 

 The same thing may be said of energy that was said of 



