Musical instruments and how they make different sounds
Physics · Key Stage 3 · The School
Strings: length and tension
A guitar string vibrates when plucked, and its LENGTH decides much of its pitch. A shorter length of string vibrates faster, giving a higher frequency and a higher note — which is exactly why pressing a string against a fret shortens it and raises the pitch. Tighter TENSION also raises the pitch, which is why players tune a string by tightening or loosening it.
Wind instruments: a column of air
In a wind instrument, it is not a string but a COLUMN OF AIR that vibrates. A longer column of air vibrates more slowly, giving a lower note — a tuba's long tube gives it a deep sound, while a piccolo's short tube gives it a high one. Opening or closing holes along the instrument effectively changes the length of the vibrating air column, which is how a single flute plays many different notes.
Pitch and loudness are separate things
PITCH depends on FREQUENCY, set mainly by length and tension. LOUDNESS depends on AMPLITUDE, set by how much energy goes into the vibration — plucking a string harder, or blowing with more force. A short string plucked gently is a high, quiet note. The same string plucked hard is a high, loud note. Length decided the pitch either way; force decided the volume.
A guitarist plays the same open string four ways. First, plucked normally: a clear note at its natural pitch. Second, plucked much harder: the SAME pitch, but louder, because only the amplitude changed. Third, a finger presses the string at the twelfth fret, shortening the vibrating length by half: the pitch jumps a full octave higher, because a shorter length vibrates faster. Fourth, the tuning peg is tightened, increasing tension: the pitch rises again, without changing the string's length at all. Four different physical changes, and each one affected either the pitch or the loudness — never accidentally both at once.