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!
How we did it:
- speaker - bluetooth
- cell phone
- popsicle stick (6)
- plastic wrap
- rubber band
- food coloring - optional
With the speaker facing up, tape six popsicle sticks around the outside of the speaker.
Cut a piece of plastic wrap large enough to cover and stretch tightly over the top of the popsicle sticks and secure with a rubber band.
Sprinkle salt onto the plastic wrap. Then, connect the speaker to the cell phone, play a song, and watch the salt move to the music!
Troubleshooting: If the salt isn’t moving, first try increasing the volume. If it still isn’t moving, try moving the plastic wrap closer to the speaker by shortening the distance between the top of the popsicle sticks and the speaker.
Optional: To see the salt more clearly, try dyeing it with food coloring! Simply combine salt and one or two drops of food coloring in a sandwich bag and shake the bag until fully mixed.