Matter and Energy 



17 



bullet shot from a gun, or in falling water. The energy of 

 motion is known as kinetic energy. Kinetic is a word of Greek 

 origin and means moving. Energy may exist and not be active; 

 then it is known as potential or latent energy, that is, energy 

 that may, under proper conditions, become active. Potential 

 is a word of Latin origin and means possible. A body of water 

 in a high place has potential energy ; a boy's muscles have poten- 

 tial energy; an elastic bow has potential energy; a bin of coal 

 contains potential energy. When water falls, its energy becomes 



Brown Brothers. 



A CONTEST BETWEEN Two FORMS OF ENERGY 



The electric engine won over the two steam locomotives. 



kinetic. When a boy kicks a football, the energy in the leg muscles 

 becomes kinetic and is shown in the form of motion. When coal 

 burns, its energy ceases to be potential and is manifest in the 

 form of heat. Energy stored in any way may, under proper 

 conditions, become active. Energy is necessary for the doing 

 of the daily tasks of every person and, in fact, for all forms of 

 life. It is important to remember that without the effects of 

 energy on matter there would be no life. 



