loudness and amplitude
when a pianist gently depresses a piano key a little hammer in the piano
taps the piano string softly making it vibrate with a small amplitude
this produces a soft sound lf the pianist bangs down hard on the key
the little hammer will strike the piano string much harder the same note
sounds much louder as the string vibrates with a much larger amplitude
similarly if you strum a guitar or blow a pipe harder you put more energy
into the vibrating system this gives rise to a larger amplitude of vibration
and therefore a louder sound by beating a drum harder you make the
skin or membrane vibrate with a greater amplitude and a louder sound
is produced the greater the amplitude the louder the sound