4.18  normal mode of vibration. Mode of free vibration of an undamped system. In general, any composite motion of the system can be analyzed in terms of a summation of normal modes.

Annotation 1          The characteristic pattern of motion typically consists of a space distribution, one part of which is negative in relation to the other part. Thus, at the same time that the particles in one part are moving outward in the positive direction from their positions of equilibrium, the particles in the other part are moving inward in the negative direction, and conversely.

Annotation 2          Vibration in a normal mode occurs at a natural frequency of the system.

Annotation 3          The terms “natural mode,” “characteristic mode,” and “eigenmode” are synonymous with normal mode.

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