Figure 1-7 (continued) 



J3 



J ;<^> Jo 



Two-way 



Work 



Gate 



This symbol represents a two-way module in which the flow of energy 

 U2) may proceed in either direction U7 or^) depending upon another 

 function. 



Sequential 

 -±2X>~ Work 

 Gate 



Heat 

 Sink 



This multiple work gate implies that a variety of energy flow inputs are 

 required for a certain resultant transformation of energy flow to take 

 place. 



A heat sink is required according to the second law of thermodynamics 

 for all processes that are real and spontaneous. All processes deliver 

 some potential energy into heat. Heat is the random wandering of 

 molecules that have kinetic energy, and it is this wandering from a less 

 probable to a more probable state that pulls and drives real processes 

 connected to such flews. 



J 



Economic Economic activity requires a transfer of energy for dollars through a 



Activity transaction. Economic activity may be thought of as an artificial 



forcing function imposed by man on a natural system. 



h 



Migratory A migratory switch requires the expenditure of energy for both export 



Switch and import of energy to the system in the form of migrating animals. 



Various switches are involved in triggering migrations such as temperature 



and insolation. 



1-12 



