POTENTIAL EXKHaV 7 



strated that it is storrd and is rccoN ci-ablf. 'I'lic simplest example 

 is the ap})heatioii of toree to a peri'ectly ehistie system. On 

 removal of the foree the system will return of itself to its original 

 configuration, and an amount of work will be done by it, in 

 returning, exactly equivalent to the amount of the force of distor- 

 tion. The hackneyed example of energy storage is, of course, 

 that of our coal supply. 



There can be no liberation of energy without free energy. No 

 change can take place without free energy. Our senses make us 

 aware of free energy, but potential energy can be perceived only 

 as the result of reasoning from past experiences. Potential energy, 

 then, is a psychological concept. 



Energy in the potential state, as long as it remains potential, is 

 useless. It cannot be transformed into any other form of energy 

 without altering its state, and its state cannot be altered without 

 the employment of kinetic energy. This point is biologically 

 important. 



1. A weight hanging from a string has potential energy accord- 

 ing to its mass and its distance from the centre of the earth, etc. 



2. An explosiv'C has potential energy depending on its chemical 

 composition and physical state. 



3. Petrol, coal, or any other fuel has similar energy bound in it. 



4. A sleeping man may be said to have potential energy. 

 In order to get w^ork out of these quiescent bodies, all that is 

 necessary is the application of a suitable and sufficient stimulus, i.e. 

 a small quantity of free kinetic energy (pp. 222 and 235). E.g. 



(1) The resistance that prevents the weight from falling must 

 be overcome, i.e. the string severed. 



(2) The explosive must be fired or detonated. 



(3) The fuel must reach ignition temperature. 



(4) The sleeper must be awaked. 



Free and Bound Energy. — In 1882 Helndioltz introduced the 

 terms " free " and " bound " to denote respectively that part of 

 the kinetic energy of a system free or available for conversion to 

 work, and that part not free or not available for this purpose. 

 Later writers, realising that potential energy as such was not 

 available for work, widened the connotation of " bound " to 

 include this dormant energy. As a matter of logical delinition, 

 only potential energy is really bound. That which is bound can be 

 freed by cutting the bonds, i.e. by doing an amount of work which 

 bears no relation to the amount of energy bound, but depends on 

 the nature of the bonds. Dissipated or degraded energy is not in 

 any true sense bound. It is not free to do work, i.e. it is not 

 available. To render it available an amount of energy woidd have 



