ABSTRACT
The models in this chapter shows how systems grow, become steady, and then decline, depending on their energy sources and their use of the sources. Exponential growth model represents a population growing on a constant-pressure source. In practice, a constant-pressure energy source cannot be maintained indefinitely, so that perpetual exponential growth is impossible. The logistic model is not limited by its source but is limited by crowding. The graph of growth on a constant-flow source is "S" shaped. It has the same shape as the logistic growth. The chapter considers model of growth in a storage tank simulated by the TANK program. It also considers the losses from storage without inflow. Some systems depend on resources drawn from a non-renewable source—for example, a population of beetles growing on the energy available from a decaying log. Both sources, renewable and one non-renewable source interact with the tank quantity which grows and provides feedbacks to the processes.
