Before we can work with systems that have time dependent behavior, we must have a grasp of its counterpart. As you may have learned in your Statics class, a static system is defined as one which does not undergo any change with relation to the time it experiences. Virtually all problems an engineer solves start by evaluating the static characteristics of the system they are studying. This is done as a preliminary measure for further evaluation and can usually give insight and often help solve particular equations; in the least it offers another equation to work with in a case where more are needed to solve for variables. A static structure is one that is resistent to externally caused forces from deforming itself or by the act of sending forces within connections to the systems boundaries. With that understanding it can be said that the notion of a system in Equilibrium brings forth a useful conceptual tool, and will in turn lead to the notion of dynamic equilibrium, which is a formulation derived from Newton's second law of motion.