LAWS OF MOTION 63 



63. Different Kinds of Energy. There are, as noted in 

 Chapter III, many forms of energy, such as chemical, elec- 

 trical, muscular, mechanical, etc. Any one form may be 

 transformed into any other form. For instance, electrical 

 energy may be transformed into chemical energy by charging 

 a storage battery; muscular energy into mechanical energy 

 by sawing a board with a hand-saw ; mechanical energy into 

 electrical energy by means of a dynamo. It is impossible 

 to create or destroy energy, but it is easy to transform it. 

 A pile-driver head weighing 75 Ibs. suspended 25 ft. above 

 the ground possesses energy, to the extent of 1875 ft.-lbs. 

 due to its position. This energy is known as static or poten- 

 tial because it is stationary. When the weight is released 

 and falls, the energy is called kinetic energy, that is, energy 

 released or due to motion. Potential energy is sometimes 

 called energy of stress; for example, the spring in a spring 

 balance is under tension when a weight is suspended from 

 the hook. Of course in all cases the weight times height 

 equals the energy of the body, 



E (potential) = W X H, 



although sometimes the velocity is given instead of the 

 height. Then the: 



WX V 2 

 E (kinetic) = - 



2 Force of gravity 



or WV 2 



K = 



This is obtained by substituting in the formula for energy, 

 for the height its value 



(Velocity) 2 

 2 Force of gravity 



