I saw this video on “Videos I found on reddit” where this guy had salt or something on a table, and he had this thing he rubbed on the table that made a sound and moved the salt into a star like shape, then he used a different object that made a deeper tone that moved the salt back, can anyone explain this? If needed i can provide a link and timestamp
In: Physics
There are 3 concepts here.
One, “tone” of a sound is its frequency, which is how many times per second the soundwave vibrates. A sound wave goes through its whole amplitude within a fraction of a second. Accordingly, there is also a wavelength, which is the distance the sound travels in that same fraction of a second.
Two, soundwaves bounce within objects. A table has a certain length which is a multiple of some wavelengths. Those wavelengths can bounce back and forth within the table and the overall wave will be “locked” in place. Depending on wavelength, size and shape of the table, they will create patterns: in some parts the wave is strong, in others there is none.
Three, small grains of salt vibrate where the wave is strong. This gives them energy to randomly move. The random move has a chance to move them into a part of the table where the wave is very weak, where they no longer have the energy to move farther so they just stay there. (It is the same as debris on the road accumulating next to the curbs – if it’s in the middle of the road it gets hit by passing cars and moves to another random place, but once it’s on the side there are no cars there to hit it back into the middle)
It sounds like you’re describing a Chladni plate. This is typically a metal plate with some dust on it, and by hitting the plate with sound (typically through an attached speaker) it is caused to vibrate.
As you might know when shaking a long stick or a pool noodle or something, some parts of the vibrating object move a lot and others can not move at all. The same applies to a vibrating plate. The parts that move a lot cause the dust to bounce around a lot and eventually bounce elsewhere. The parts that stay still don’t bounce the dust away, and so all of the dust slowly collects there. This forms dust patterns that mimic the parts of the plate that don’t move.
By adjusting the sound frequency, you can change the way that the plate vibrates, and so the parts that stay still, and so the dust patterns on its surface.
The table vibrates with the sound waves. Where the waves have a high amplitude point the salt vibrates away and gathers where the wave doesn’t move the surface of the table as much.
It’s like [this](https://www.youtube.com/watch?v=-gr7KmTOrx0) but not on a simple wire but a whole surface so you get 2D patterns.
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