Modal analysis or other methods are used to model systems. Such models are used to predict motion, sound generation, and load on the structure to predict failure . In understanding vibration it is important to distinguish between the types of force signals that may initiate oscillation and the types of resulting response. The figure to the right illustrates the major types of signals and responses. Stationary signals are statistically stationary, they do not change over a sampling period.
Deterministic signals are the opposite of random signals that have no distinct components.
Finally, signals may be continuous or transient in nature. Impacts or other sudden events may generate transients.