Harmonic Motion is the fundamental motion of all kind of matter as it has been shown that matter exists both as particles and as waves. So an understanding of waves (generated by harmonic motion) is as necessary as the understanding of particle dynamics. This site deals with the wave part of matter in the classical way going gradually towards quantum mechanics. If you have a good link to add to this category, please do so.

This is a reformulation of Newton's Laws of Motion, developed by W. R. Hamilton and J. L. Lagrange, using Hamilton's principle of least action and then further analysing the resultant formulae using methods in calculus of variations.