Frequency Modulation

I have found this video where he shows how FM differs from AM based on the changes on frequency in a wave instead of its amplitude.  It shows how the carrier change its frequency overtime by the modulator.

Also, on Partials, is very simple to know that when we hear any sound of a vibrating object (such a musical instrument) the sound we hear contains obviously many different frequencies and pitches and the combination of those two concepts is what is called Partials. So, wrapping all up, this collection of frequencies, pitches, or partials is what we define as Harmonic Series or Overtone Series.