You may have done this experiment in school before. If not, it’s worth doing it for the sheer magical effects. Sprinkle some sand over a solid metal plate. Then rub a violin bow along the edges to make it vibrate. If you don’t have a violin, attach a speaker to the metal plate. When audio is played through the speaker at the right frequency, it will resonate and vibrate. Watch what happens. As if by magic, the grains of sand will rearrange themselves into beautiful geometric patterns with a high degree of symmetry. These patterns are called Chladni patterns, named after the German physicist and musician, Ernst Chladni (1756-1827).

Chladni patterns can be readily explained by science [1]. Every material, including water or a metal plate, has a natural resonant frequency (a set of frequencies at which it vibrates), set off by lines where it won’t vibrate. These are called nodal lines. When a metal plate vibrate at one of those resonant frequencies, the sand will be pushed away from the vibrating regions and cluster along the nodal lines. Change the frequency and you will also change the locations of the vibrational nodes, and get a different set of patterns.

Here is a demonstration of the Chladni effect.

Chladni was not the first to discover these acoustic patterns. A century earlier, the English polymath, Robert Hooke (1635-1703) explained that the nodal lines on a metal plate are analogous to nodal points along a vibrating string – points where the string divides itself into different segments, each vibrating independently of the others. But the patterns were named after Chladni because he was the first person to conduct in-depth investigations into the phenomenon. As you might expect, makers of musical instruments became fascinated with the technique and violin makers in particular used it as a vital tool for making violins. At a more abstract level, Chladni patterns even made their way into quantum physics when the renowned quantum physicist, Erwin Schrodinger used the mathematics of nodal patterns to arrive at the understanding of electron orbitals [2]. Sadly, Chladni’s name is now largely forgotten even though his discovery has a literally visible impact on science.

Notes

[1] The scientific study of visible sound and vibration patterns is called Cymatics.

[2]  J. Michael McBride, “Chladni Figures and One-Electron Atoms”, Lecture #9, Freshman Organic Chemistry (CHEM 125) course, Open Yale Courses, Yale University, video recorded Fall 2008, accessed on YouTube, https://www.youtube.com/watch?v=5kYLE8GhAuE, 2016-06-05.