Newton’s Laws as an Interpretive Framework in System Dynamics

This paper proposes an interpretative framework for system dynamics models using concepts from Newtonian mechanics. By considering the second derivative form of a model, it is shown that Newton’s three laws of motion have their equivalent in system dynamics, with forces between stocks being determined using the loop impact method. The concepts of mass, inertia, momentum, and friction are explored as to their usefulness in understanding model behaviour. The Newtonian framework is applied to two standard system dynamics models, inventory-workforce and economic long-wave, where their behaviour is analysed using force dominance on the stocks interpreted through the framework. Results show improved intuitive understanding of system behaviour compared with existing dominance methods, particularly for models with exogenous effects, oscillations and many loops. The framework is commended for further exploration.