The guitar is a typical string instrument, whose physics are similar to many other string instruments. The main parts consist of the body, the neck, the bridge, the tuning pegs, the sound hole, and the strings. An electric guitar lacks the sound hole and instead relies on an amp for amplification. The physics of a guitar involves sound waves, how they are amplified, and how they travel.
The vibration of the strings of a guitar causes the sound wave, but is not actually what you are hearing. The amplification of the sound wave is what is actually heard. The differences in the tension of the stings and the mass of the strings affect the pitch of the sound produced. The ends of each string are nodes, or where the wave does not travel from its initial position. The note you hear from the string is actually the first harmonic of the wave; other harmonics created when plucking a string form the undertones and overtones of a note. The waves on a guitar string are transverse waves, meaning they travel perpendicular to the original position. The waves are also standing waves, because they remain in the same position.
Strings are tuned to match certain harmonics, and frets are carefully placed to create certain frequencies. For a standard guitar with 24 frets, it would be calculated so that there are two octaves, divided at the twelfth fret. The ratio between two adjacent frets is equal to the square root of two on a guitar with twenty-four frets. This ensures that certain notes can be produced, while keeping the length of the six strings equal. If a guitar has more frets then calculating their distance becomes more complicated.
The differences in tension to produce different pitches are created by tuning the guitar, using a capo, or pressing down on a string within a fret. Guitars can be tuned differently to produce a different range of notes. Less tension equals a lower note while greater tension equals a higher note. For example, tuning a guitar in drop-D would lower the sound of the low E-string by lessening the tension on that string. Playing an open string has the lowest sound possible for a specific tuning. As you push down frets closer to the sound hole, you increase the tension on the string, raising the pitch of the note. Using a capo has the same effect as pushing down a string with your finger, except it pushes down all six strings at once; it increases the tension of the string, thus raising the pitch of the note.
The mass of a string also creates variation in the pitch of the strings, while keeping them all the same length. A greater mass of a string causes the string to vibrate slower, lowering its pitch. The lower strings on a guitar have thicker strings, which helps to lower their pitch. Higher strings are thinner, raising their pitch. In classical guitars, (not including traditional classical guitar strings made out of sheep or cow intestine) this difference in mass is created by using different materials....