How do musicians change the pitch of sound ?

A perceptual characteristic of sounds that enables their arrangement on a frequency-related scale, or even more generally, pitch is the quality that makes it feasible to classify musical melodies as higher and lower, thus known as Pitch. The string's four characteristics that influence its frequency include length, diameter, tension, and density as outlined below:

If a string's length is modified it may vibrate with another frequency. Shorter strings are higher in frequency and hence higher in pitch. When a musician clicks a string on his finger they shorten his length.String thickness is diameter. Thick strings with broad diameters vibrate slower than thin ones and also have lower frequencies.A string extended between two points would have tension, as on a stringed instrument for instance. Stress refers to how strongly you stretch the string.A string's length can influence its frequency, too. The dense molecules vibrate at higher velocities. The slower it vibrate as denser the string and the lower will be its frequency.

The rocks expand when there hot/warm  and contract when they are cold.