Whenever a musician plays a guitar, they pluck one of the guitar strings to produce a standing wave in the string. Then pinch down on the string at the other end at the guitar in different places along the neck of the instrument. In doing so, by changing where they pinch the string, the same standing wave on that string can produce multiple different frequencies, and therefore multiple different notes. Using the knowledge you have learned about harmonic frequencies set up on strings, explain why simply changing where you pinch the string can change the frequency.