Under normal circumstances, dropping an entire bowl of couscous is justification for burning down your whole house and starting a new life, one where you don’t need to spend a decade finding pieces of grain on the floor. That is, unless you just happened to drop them on a metal plate that can simply turn that disaster into a beautiful pattern.
In this video from Steve Mould, he shows us how a seemingly random mess can instantly transform into an organized piece of art using a piece of metal and a bow.
First he randomly spread some couscous (though he could have used any similar item such as sand) onto a metal sheet known as a Chladni plate. Then, using a musical bow he strummed the side of the plate, which in turn created a symmetrical and elegant pattern out of the couscous. Depending on where he strummed the plate he produced a different frequency which then produced a different pattern.
German scientist Ernest Chladni (1756-1827) discovered this phenomenon while studying the motions of vibrating plates (how fortunate the plates share the same name as the guy who discovered them). From the Smithsonian’s page on him:
“Starting with a metal plate whose surface had been lightly sprinkled with sand, he found that bowing it produced characteristic patterns that could be related to the physical dimensions of the plate. ‘Chladni’s Plates,’ as they came to be called, provided an early way to visualize the effects of vibrations on mechanical surfaces.”
As Mould explains in the video, the couscous isn’t exactly being moved to those spots, but rather the grains are stopping there, because those patterns are made by where the plate isn’t moving at all–they are a resting place.
Turns out that the math behind the process was a little too much for Chladni himself, but fortunately mathematician Sophie Germain (1776-1831) was able to work out what was a problem of wave dynamics. As Mould said, “Wave dynamics is a subject that permeates all of physics.”
Unfortunately for her, she was not recognized for her work during her lifetime. Only after her death was her contribution celebrated.
Both Chladni and Germain deserve their accolades, because beyond just being really cool to watch, this discovery had tangible applications, as it “did much to improve the standing of acoustics during (Chladni’s) lifetime, and inspired many of the acoustic researchers who later extended his work. ”
“Once Chladni’s patterns began to be understood, it was found that they could also be used analytically, to provide information about the conditions that formed them. For example, violin makers have long used Chladni figures to provide feedback as they shape the critical front and back plates of the instrument’s resonance box.”
While other technologies have replaced most of the analytical applications of Chladni’s plates, “Chladni patterns are still of scientific interest.”
Sure, computers can be used to figure out these vibrations now, but that isn’t nearly as cool as watching a plate of spilled couscous suddenly turn into the wheel of a ship.
What other scientific demonstrations are your favorite ways of understanding more complex concepts? Share them with us in the comments below. Why? Because science.
—
Images: Steve Mould
