Abstract
Separate energy equations for potential energy, kinetic energy of averaged motion, kinetic energy of eddy motion, and thermal energy are derived on the basis of four postulates concerning natural processes. The equations are transformed for use with space- and time-averaged values of the dependent variables in a general system whose boundaries have arbitrary shape and motion. The equations are written in a manner that makes apparent the significance of energy transformation functions, which are the mathematical expressions of the physical mechanisms by which one kind of energy is transformed into another.