Re: Explain how you can change the pitch of a stringed instrument.

The wavelength of the fundamental wave on a stringed instrument is twice 
the length of the string.  The frequency of the fundamental wave on the 
string is controlled by the mass of the string and the tension in the 
string.  The frequency of the string is what determines the pitch.  The 
relation may be expressed as an equation:

frequency = sqrt{Tension/(4*Mass*Length)}

Thus, if you increase the tension by turning a tuning peg, the frequency 
increases.  In addition, if you shorten the string by pushing it onto a 
fret, then the length decreases and again the frequency increases.

On an instrument like a washtub bass, you change the tension in the string 
to change the frequency.  On an instrument like a guitar, you shorten the 
string by pushing it onto a fret.