530 GEOLOGY 



Kinds of energy and force. Ultimately the forms of energy may 

 be reduced to a few, and possibly to a single kind. Indeed, some phy- 

 sicists believe that all forms of energy are really but different mani- 

 festations of kinetic energy. But the number of elementary kinds of 

 energy in the universe is a problem for the physical philosopher, not 

 the geologist. The geologist is concerned in all the kinds of energy 

 which he observes at work. These are: (1) gravitation energy, (2) 

 heat, (3) elasticity energy, (4) cohesion energy, (5) chemical energy, 

 (6) electrical energy, (7) magnetic energy, (8) radiant energy (in- 

 cluding radiant heat, radiant light, and electromagnetic radiation). 1 



From another point of view energy may be classified into kinetic 

 energy and potential energy. Under static conditions of all the parts 

 of a system any or all of the kinds of energy above named may be 

 exerting force, but so long as no motion occurs and no work is done 

 they are all potential. When anywhere in the system movement takes 

 place and work is done, some portion of the energy becomes kinetic. 

 Work and kinetic energy are inseparable. As multifarious kinds of 

 work are always going on in the world, potential and kinetic energy 

 are always existent. For the most part we can trace the kinetic energy 

 back to one or more of the various classes of energy above mentioned, 

 but some part of it may be derived from other unnamed sources. 



Any of the forms of energy may exert force, hence we have the 

 terms "force of gravitation," "force of heat," "force of elasticity," 

 "force of cohesion," "chemical force," "electrical force," "magnetic 

 force," and "radiant force." 



Any or all of these forces may be exerted both under static and 

 dynamic conditions. When the conditions are static, the energy is 

 potential. When the conditions are dynamic and work is done, 

 some portion of the energy is kinetic. To illustrate: For many years 

 a cliff may stand; but finally a portion of it falls and geological 

 work is done. The force of gravitation is exerting the same pressure 

 upon the material concerned during all the years of quiescence and 

 during the brief period of movement, and, for that matter, continues 

 to be exerted after movement ceases. During the static conditions 

 the energy of gravitation is potential. During movement some part 

 of it, by pressure of the force of gravitation, passes into kinetic 

 energy. And this energy, through the agency of the falling part, the 

 agent, does further geological work upon the material at the foot of 

 the cliff. 



All of the forms of energy and force are important in geology, 

 but the geological work of some of them has been more clearly dis- 

 criminated than that of others. For instance, the geological results 

 produced by electricity and magnetism have not been worked out, 

 although I have no doubt that electrical and magnetic energy have 

 1 Silas W. Holman, Matter, Energy, Force and Work, p. 37, 1898. 



