Making music: how different instruments produce pitch
Physics · Key Stage 2 · The School
Three families, three vibrations
STRING instruments, like a guitar or violin, make sound with a vibrating STRING. WIND instruments, like a flute or trumpet, make sound with a vibrating COLUMN OF AIR. PERCUSSION instruments, like a drum, make sound with a vibrating SURFACE, such as a stretched skin. Every instrument, in every family, still obeys the same basic rule. No vibration means no sound.
Changing pitch on a string
A string instrument changes pitch mainly by changing the LENGTH of string that is free to vibrate. Pressing a guitar string against a fret shortens the vibrating part. A shorter length vibrates faster, giving a higher note. Tightening a string does something similar. A tighter string also vibrates faster.
Changing pitch on a wind instrument
A wind instrument changes pitch mainly by changing the LENGTH of the air column that vibrates. Opening a hole on a recorder effectively shortens the column of air. That gives a faster vibration, and a higher note. Covering more holes lengthens the vibrating air column instead. That gives a slower vibration, and a lower note.
A recorder player covers every hole and plays a low note. They lift one finger, uncovering a hole near the bottom. The note rises. A guitarist plays an open string, then presses it down near the middle of the neck. The note also rises. Both musicians just did the exact same thing, in different ways. They shortened the length of whatever was vibrating. A shorter vibrating length always means a faster vibration, and a higher pitch.