• 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 its behaviour for an initial… Read more: Energy in System Dynamics Models
  • 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 of the force is measured… Read more: Force and 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 population will decline over time… Read more: Balancing Loops: Growth and Decline
  • 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 people reverse the argument: the… Read more: Reinforcing Loops and Growth