What is harmonics in electronics and in sound?

[vitality00]

Please explain thanks with analogies, I have hard time understanding from wikipedia,

 

more practical/real life example would be good thanks

[swansont]

A vibration that happens at f (with a certain wavelength) can also easily happen at 2f, because all of the same boundary conditions apply. So vibrations at multiples of f can be seen in some systems.

 

In the wikipedia example http://en.wikipedia.org/wiki/Harmonic#mediaviewer/File:Moodswingerscale.svg you can see that the condition you have to meet is that you have no vibration at the endpoints. For a standing wave, you need an integral number of half-wavelengths. If 1/2 wave is at f, a full wave (2/2) is at 2f and 3/2 wave is at 3f. And so on. Those higher frequencies are the harmonics.