The length of a string is inversely proportional to the frequency of the sound it produces. This means that longer strings produce lower sounds, while shorter strings produce higher sounds.
String tension
The tension of a string is also inversely proportional to the frequency of the sound it produces. This means that strings that are tighter produce higher sounds, while strings that are looser produce lower sounds.
String thickness
The thickness of a string is directly proportional to the frequency of the sound it produces. This means that thicker strings produce lower sounds, while thinner strings produce higher sounds.
In summary
The three main factors that determine the pitch of a sound produced by a string are its length, tension, and thickness. Longer, looser, and thicker strings produce lower sounds, while shorter, tighter, and thinner strings produce higher sounds.