Author: John Hayward


Energy in System Dynamics Models

Kinetic Energy Energy, a familiar concept in Newtonian mechanics, is a valuable way of describing behaviour in system dynamics models. For example, consider a stock with a constant flow, figure 1: For a positive value of f, stock x increases uniformly over time. The top graph of figure 2 shows […]

Force and Impact, Loop Impact

Force and Impact

In mechanics, force produces acceleration in an object. The same concept can be used in system dynamics to describe how any time-varying signal can cause acceleration in a stock – a dynamic variable. That signal may be exogenous or come from another stock. In the Newtonian Interpretive Framework, the effect […]

Loop Impact

Balancing Loops: Growth and Decline

Early on in a system dynamics (SD) course, it is usual for a learner to be introduced to two types of first-order balancing loops: one where the stock grows, and one where the stock declines. Death Process Take the decline situation first. If there are no births or migration, a […]

Force and Impact, Loop Impact

Reinforcing Loops and Growth

I have often seen the following causal loop used in system dynamics presentations to explain a reinforcing loop: Figure 1: Causal Loop Diagram of Simple Birth Process The argument then runs: the more population, the more births, hence more in the population; thus,“ the population grows. Fortunately, I never hear […]