Discover how music creates vibrations you can see using salt and a portable speaker! Then try experimenting with different genres of music to see which ones make the salt dance more.
What's going on?
Speakers, like your Bluetooth speaker, produce sound by creating vibrations in the air. Normally, we only hear these vibrations, and we can't easily see them. Plastic wrap, though, is lightweight and thin enough to vibrate in response to the sounds coming from the speakers. These vibrations move through the plastic wrap unevenly, pushing and shoving the salt around in interesting patterns. As a song progresses, these vibrations change, and the salt moves as if it were dancing.
If you can find a YouTube video of a pure tone (like a single, sustained note), observe what happens to the salt when you play that tone through the speakers. A pure tone will create a consistent, unchanging vibration in the plastic wrap. Instead of dancing around, the salt should collect in places in the plastic wrap that aren't vibrating, making patterns that depend on the frequency of the pure tone. Try a few other pure tones, one at a time, to see some other interesting patterns!