Questions about the tone of musical instruments

The harmonica is a fixed-tuned instrument. Because there are no other changing tones, the key is single. The piano has 88 keys. It is an instrument made based on the concept of twelve equal temperaments. Each key is arranged according to the rules of semitone relationship, so its key changes are very random. The whole tone and the whole tone between the scales of each key are Semitone relationships can all be realized on the piano. There are frets on the fingerboard of the guitar. One fret has a whole-tone relationship, and adjacent frets have a semi-tone relationship, so the principle is the same. In addition, the guitar can also be transposed with the help of a capo. When the key is different, first of all, the tonic is different, and the chords in the key are also different, because the relationship between whole steps and semitones in the original key is destroyed and moved to another key and rearranged, so the key changes, and each note in the key is also different. no the same.