The true physics of guitar strings is very complex, but the basic theory is quite straightforward. The starting point is that the fundamental frequency of vibration of a string is inversely proportional to its length and directly proportional to the square root of the tension. This frequency is also inversely proportional to the square root of its mass per unit length. So the frequency that sounds when you pluck a guitar string is a combination of these three properties - length, tension and mass. read more »