What happens when you throw sand or salt on a metal plate resonating at different frequencies? This does. Dubbed cymatics, it shows the difference between the regions of maximum and minimum displacement in the plate at different frequencies, creating amazingly beautiful geometric patterns.
The experiment shows the nodal patterns from vibration on a Chladni plate. As the frequency rises, the patterns get more and more complex.
But how does it work? Well, as you subject the plate to different frequencies, the very molecules of the metal plate resonate, making them vibrate. But they don't vibrate evenly - some parts of the plate vibrate more than others, thanks to the soundwaves reverberating through the plate.
When a substance like salt or sand is placed on the top of the plate, it automatically shifts to the areas where the plate is vibrating the least, creating these weird geometric shapes.
It doesn't have to be done with just salt on a plate though - check out this video of cornstarch being played on a speaker at 60Hz:
Some of the patterns are amazingly complex and stunningly beautiful. If you're interested in creating your own Chladni plate to try this experiment for yourself, you can make a fairly basic chadni plate following these instructions here.