Here's an example of how a guitar gets tuned, and how tension effects pitch (click below).
Here's an example of me playing acoustic guitar, demonstrating how music can be played when intonation and pitch are correct (click below).
Here's an example of electric guitar, when the pitch and intonation are correct (click below).
Here's an example of manually altering the pitch, by bending the string and increasing/decreasing the tension of the strings (click below).
