Higher-pitch tone made when a section of a string vibrates faster than the whole string?

Answer 1

The higher pitch heard is known as a harmonic, so called because two or more parts of a string vibrate together in a perfect balance.

The pitch of a string is obtained by a combination of tension and "scale length".

For example; if the full length fifth string on a guitar is plucked, without being touched, and the correct tension is set, it will give an A2 - 110 Hz. This means that the whole string vibrates back and forth 110 times per second.

If you hold your finger at the fret exactly half way along the string, it will play A3 - 220 Hz.

Now some skilled players adopt a technique where the finger just lightly and briefly touches the string at the mid point while it is plucked, this stops the whole string from moving and instead causes a "pivot point" where the string now vibrates at the rate of A3 in a kind of "S" shape. The same technique can be achieved at the "one third" point, giving an E4 - 329.63Hz, the string now vibrating in three separate places with two pivot points.

Depending on the quality of the equipment and the way it is picked up and amplified, it is possible to produce many different harmonic notes. This is how some Rock Guitarists can produce that very high "squeal" at a pitch above any of the natural notes on the fret board.