Editing Normal mode (section)

{{Short description|Pattern of oscillating motion in a system}}
{{No footnotes|date=December 2010}}
A '''normal mode''' of a [[dynamical system]] is a pattern of motion in which all parts of the system move [[sinusoidal]]ly with the same frequency and with a fixed phase relation.  The free motion described by the normal modes takes place at fixed frequencies.  These fixed frequencies of the normal modes of a system are known as its [[natural frequency|natural frequencies]] or [[Resonance|resonant frequencies]].  A physical object, such as a building, bridge, or molecule, has a set of normal modes and their natural frequencies that depend on its structure, materials and boundary conditions. 

The most general motion of a linear system is a [[Superposition principle|superposition]] of its normal modes. The modes are normal in the sense that they can move independently, that is to say that an excitation of one mode will never cause motion of a different mode. In mathematical terms, normal modes are [[Orthogonality|orthogonal]] to each other.

[[File:Drum vibration mode12.gif|right|thumb|248px|Vibration of a single normal mode of a circular disc with a pinned boundary condition along the entire outer edge. [[:commons:Category:Drum vibration animations|See other modes]].]]
[[File:A cup of black coffee vibrating in normal modes.jpeg|right|thumb| A flash photo of a cup of black coffee vibrating in normal modes]]
[[File:Spherical harmonic in water drop.ogv|thumb|Excitation of normal modes in a drop of water during the [[Leidenfrost effect]] ]]