FreeMusic theory

Musical instruments produce sound waves or 'energy' in a vibratory motion by beating, blown, plucked, struck or frictionized with  a bow.  Now, on the piano, when you strike a note you assume you are hearing only one note, but you are not.  You are simultaneously hearing a series of higher tones that are sounding at the same time.  These tones are arranged by nature and rules by physical laws.
     When striking a string on the piano, you are not only playing the whole string but also fractional parts of the string.  It is as if the string is divided into halves, thirds, quarters etc.  The smaller the segments the faster the vibration and the higher the tones, thus the overtone series.
     These overtones (harmonics) are all sounding together producing the full string. As is apparent the tones sounding more faintly as they move higher.  There is an overtone series on every note we strike, but the tones are more audible when striking the lower notes.  That is why when striking lower tones
they have a richness and fullness that the higher tones to not have.  In other words, we can hear more of the overtones when striking the lower notes.