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Normal mode and eigenfrequency

  1. Aug 11, 2008 #1
    What is the difference between eigenfriquency and normal mode? If, for example, I solve the secular equation (from the equations of motion) for a mechanical system (say two masses on springs) to obtain the eigenvalues I thought I got the normal modes, but now Im told I get the eigenfrequencies..`?

    Thanks for any help to enlighten me on this matter.

  2. jcsd
  3. Aug 12, 2008 #2
    The normal modes are the eigenvectors, the eigenvalues are what are also known as eigenfrequencies. Example Af=wf, where A is your operator (could be differential like d/dx etc), f is a function, w is the eigenvalue/eigenfrequency. If you solve this to find the functional form of f, then you have obtained the normal modes or eigenvectors as theyre also known. For each function f you find, you will also get a value of w.....f1:w1, f2:w2 etc, these values of w are the eigenfrequencies.

    So for the equations for two masses on a spring, the functions that describe the motion of the masses, and their amplitudes of vibration are your normal modes . To each of these normal modes will correspond a frequency of vibration, the eigenfrequency.
  4. May 17, 2009 #3
    nice explanation
  5. Jul 6, 2009 #4

    It nice explanation :-)

    I hve question.. what about the Transverse frequency, which systems ossillate if some electromagnetic radiations (e.g light) shines on the material.

    Best regards
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