Metal plate resonance experiments using only household items
I had seen a few experiments showing resonance on a metal plate, there are lots of examples on YouTube. It's also called a "Chladni plate".
I had the idea of trying to reproduce such an experiment using really basic means.
So instead of fancy equipment, I'm using a tablet computer, some computer speakers, a cookie sheet, and some salt.
The first thing to figure out is what frequencies the cookie sheet will resonate at. I installed the "Spectrum Analyze" app on my Android tablet. I tapped the cookie sheet and watched the spectrum display to see which frequencies the cookie sheet liked to resonate at.
Next I used an app called "Frequency generator" on the tablet to make that frequency of sound.
I supported the cookie sheet above a computer speaker. The speaker is facing up and I turned it up loud while the 178 Hz tone was playing. Spreading some salt on the cookie sheet revealed the modes of vibration.
The cookie sheet has a standing wave pattern on it, where some parts deflect upward while other parts deflect down. The areas in between move very little.
The salt in areas of strong vibration tends to bounce away from those areas and settle where vibrations are weaker. So the lines formed by the salt show the "nodes" of the vibration — areas between the stronger vibrations.
Trying a lower frequency. The area of the cookie sheet is divided into three, left top corner, middle and right 40%. Basically, the left top corner and the right side move up at the same time that the remaining area (middle to bottom left corner) moves down, and vice versa, and the salt settles in between.
When I turned the sound off, and pushed the middle of the speaker, I could hear the speaker's voice coil scratching against the magnet. The speaker was shot.
So I tore it open to see the damage. The voice coil was blackened (it's normally red magnet wire). The heat had caused it to distort, and then it rubbed against the magnet.
I also switched from salt to sand so it would show up better against the white surface.
It's really cool how, after dialling in a frequency, the pattern slowly emerges in the sand.
I wasn't able to get results as clean or spectacular as other experiments on YouTube, but the cool thing is, I was able to do these experiments without using any scientific equipment - using just regular household items!
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