In calculating natural frequencies and mode shapes, the applied loads (either forces or acceleration, e.g., gravity “g” loads) do not play a role. However, when we speak of a system’s failure in a shock or vibration environment, we are making a reference to the deflection (and by necessity to stress) at a critical point in the system. These values cannot be evaluated without knowledge of the applied loads on the system. This necessitates our understanding and evaluation of the dynamic loads acting on as well as the behavior of the deformable structure. Here, the assumption of a spring-mass may no longer be accurate.