A couple days ago I was doing some stretching on the carpet and I was looking upwards at the ceiling fan that cools our apartment. It was on, so all I could really see was a ghostly circle as the arms of the fan rotated too fast for the eye to observe. It struck me that this was exactly what happens when you hear a note of music. A note is really a series of vibrations but they happen so quickly that our ear hears them as one “thing,” one—to use a fancy term—percept. The ghostly, circular image of the ceiling fan is the visual equivalent of that percept. It’s moving so fast that our eye turns it into one object (albeit an ethereal, hazy one.)
The best illustration of how a note is really many vibrations is the sound of a helicopter starting up. It’s starts with a series of Whoop… Whoop…Whoops that get faster and faster—WhoopWhoopWhoop, until they just sound like a single Whirr, usually with a definite pitch. Many Whoops equals one Whirr.
Anyway, just wanted to share my observation.