A more complete analysis of heat transfer depends on further information about the mechanisms by which energy is driven from a higher to a lower temperature. Long experience has shown us that there are three primary mechanisms of action: conduction, convection, and radiation. The study of heat transfer involves developing a quantitative representation for each of the mechanisms that can be applied in the context of the conservation of energy in order to reach an overall description of how the movement of heat by all of the relevant mechanisms inf luences changes in the thermal state of a system.