Thus far have considered only static response. However, things also move, this includes structures Can actually identify three \categories\ of response A.(Quasi)-Static [quasi because the load must first be applied
Now consider the case of compressive loads and the instability they can cause. Consider only static instabilities (static loading as opposed to dynamic loading [ e.g., flutter) From Unified, defined instability via a system becomes unstable when a negative stiffness overcomes
