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Monday, June 24, 2013

The Amazing Resonance Experiment

This is truly amazing. It's just a vibrating plate with some salt on top, but the shapes that the salt takes at different frequencies is totally unexpected. I searched the Web but couldn't find any explanation for why this happens, although I'm sure it's a known phenomena.

Any physicists care to jump in with an explanation?

The full 8 minute video is found here.


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13 comments:

Chris Foster said...

Cymatics: http://www.youtube.com/watch?feature=player_embedded&v=cy2Dg-ncWoY

Dr Colin Webber said...

Chladni patterns. The plate resonates in regular sized zones according to harmonics, much like the series in a string or pipe. The salt collects at the modes, where the plate is still. There are some nice infra-red images of these resonant patterns on violins and guitars around on the net, which suggest that the great violin makers had a pretty good understanding when they shaped the body and internal structures of the instruments.

Enig Mue said...

reminds me of Aztec symbols or something, very interesting/cool

Jon Dayton said...

It's a good visualization of what goes on inside a plate reverb. It's basically a two dimensional audio environment where the sound mostly bounces off the four edges of the plane.

Will Castillo E said...

... " All objects have a frequency or set of frequencies with which they naturally vibrate when struck, plucked, strummed or somehow disturbed. Each of the natural frequencies at which an object vibrates is associated with a standing wave pattern. When an object is forced into resonance vibrations at one of its natural frequencies, it vibrates in a manner such that a standing wave is formed within the object. The topic of standing wave patterns was introduced in Unit 10 of The Physics Classroom. In that unit, a standing wave pattern was described as a vibrational pattern created within a medium when the vibrational frequency of a source causes reflected waves from one end of the medium to interfere with incident waves from the source, The result of the interference is that specific points along the medium appear to be standing still while other points vibrated back and forth. Such patterns are only created within the medium at specific frequencies of vibration. These frequencies are known as harmonic frequencies or merely harmonics. At any frequency other than a harmonic frequency, the interference of reflected and incident waves results in a disturbance of the medium that is irregular and non-repeating.

So the natural frequencies of an object are merely the harmonic frequencies at which standing wave patterns are established within the object. These standing wave patterns represent the lowest energy vibrational modes of the object. While there are countless ways by which an object can vibrate (each associated with a specific frequency), objects favor only a few specific modes or patterns of vibrating. The favored modes (patterns) of vibration are those that result in the highest amplitude vibrations with the least input of energy. Objects favor these natural modes of vibration because they are representative of the patterns that require the least amount of energy. Objects are most easily forced into resonance vibrations when disturbed at frequencies associated with these natural frequencies.

The wave pattern associated with the natural frequencies of an object is characterized by points that appear to be standing still. For this reason, the pattern is often called a "standing wave pattern." The points in the pattern that are standing still are referred to as nodal points or nodal positions. These positions occur as the result of the destructive interference of incident and reflected waves. Each nodal point is surrounded by antinodal points, creating an alternating pattern of nodal and antinodal points. Such patterns were introduced in Unit 10 of The Physics Classroom Tutorial. In this unit, we will elaborate on the essential characteristics and the causes of standing wave patterns and relate these patterns to the vibrations of musical instruments.

A common Physics demonstration utilizes a square metal plate (known as a Chladni plate), a violin bow and salt. The plate is securely fastened to a table using a nut and bolt. The nut and bolt are clamped to the center of the square plate, preventing that section from vibrating. Salt (or sand) is sprinkled upon the plate in an irregular pattern. Then the violin bow is used to induce vibrations within the plate; the plate is strummed and begins vibrating. And then the magic occurs. A high-pitched pure tone is sounded out as the plate vibrates. And, remarkably (as is often the case in a physics class), the salt upon the plate begins vibrating and forms a pattern upon the plate. As we know, all objects (even a silly little metal plate) have a set of natural frequencies at which they vibrate; and each frequency is associated with a standing wave pattern. The pattern formed by the salt on the plate is the standing wave pattern associated with one of the natural frequencies of the Chladni plate. As the plate vibrates, the salt begins to vibrate and tumble about the plate until it reaches points along the plate that are not vibrating. Subsequently, the salt finally comes to rest along the nodal positions " ...

Anonymous said...

Thinking like an audio geek.... these are standing waves and are probably defined by the dimensions of the plate as well as the frequency of the oscillation. Using a pure sine tone (which lacks elaborate harmonics) makes the illustration more dramatic. The sound waves sum and cancel at specific points on the metal plate where sound radiates from the center and bounces back from the edges (as the density change at the edges of the plate to the surrounding error creates reflections). I suspect that the salt accumulates at the cancelling points of the wave reflections and is driven away from the summing points (where greatest oscillation will take place).

Mor10 said...

Here you go: http://www.physicsclassroom.com/Class/sound/u11l4c.cfm

Anonymous said...

Reminds me of electron shells around the nucleus of atoms...

Anonymous said...

Lovely except for the crappy music accompaniment. Why not let us hear the tone that makes the pattern?

Doug said...

That is just awesome!

Cymber Lily Quinn said...

Thanks for posting this. Understanding how sound affects physical objects is the basis of the sound healing arts.

As others have written, different materials vibrate at different frequencies, and present different patterns. The same is true with the body. Nerve tissue vibrates at 2Hz, for example. Bone at 10Hz (both of these are approximate numbers). Research on bone growth using electronic stimulus has been going on at Research Triangle Institute in Raleigh, North Carolina, and the University of Colorado-Boulder for a while.

If the tissue is vibrating at a different frequency that its native frequency, that's what we call disease. As the tissue restores to its native frequency, that's what we call health.

I have long wondered what cancer or heart disease sounded like from a frequency point of view.

But more importantly, it is possible to provide an external stimulus (in my case, it's my harp), that will override the offending frequency and return the tissue to its native frequency.

Many instruments can do this including the harp, flute and Tibetan chimes. It can also be done electronically with various lasers and frequency generators, such as the one developed by Dr. Carol McMakin in Portland, Oregon.

Understanding frequencies in the body, I hope, will open whole new fields of medicine and healing that work less invasively and more naturally.

rachelroust said...

That's rad.

NotAMoby said...

Lolz you can just use cardboard!!!!!

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