= Solution
A <normal mode> is a fixed displacement pattern whose components share a common harmonic time dependence in the equations for <small oscillations>. Its <normal frequency> is the associated oscillation frequency; below, $\omega$ denotes the angular frequency, so the frequency in cycles per unit time is $\omega/(2\pi)$. A <normal coordinate> is the amplitude of one such pattern, chosen so that the linear equations decouple. For <mass matrix> $M$ and <stiffness matrix> $K$, the patterns solve $Kv=\omega^2Mv$. Zero eigenvalues describe free rigid motions rather than periodic restoring oscillations.
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