Taking on a New Shape

May 15, 2006 feature
Rotating Polygons
Rotating Polygons. Credit: Thomas Jansson.

“It is seldom that you see a new stable structure appearing spontaneously in a completely symmetric environment,” explains Tomas Bohr, a physicist at the Technical University of Denmark. “Usually you have to do something to break the symmetry. But we’re not doing anything to break the symmetry. The system does it all by itself.”

The unusual phenomenon in question involves rotating a bottom plate under a liquid in a circular (cylindrical) container. Bohr and his team of students at the Technical University and at the Niels Bohr Institute set up an experiment to find out whether or not such conditions would lead to stable deformations of a water surface into polygon shapes. The findings from their experiment were published May 3rd in Physical Review Letters.

Rotating Polygons.
Rotating Polygons. Credit: Thomas Jansson.

Bohr tells PhysOrg.com that a somewhat similar experiment took place eight years ago with a different team (including Clive Ellegaard and others). “We had fluid falling on a plane, like water from a faucet. We found that even if the rim of the plate is completely circular, the fluid surface can be shaped like a polygon.”

While the first polygon experiment Bohr did involved stationary polygons, the most recent effort shows rotating polygons. “Not only are these shapes rotating,” says Bohr, “but they are rotating at a different speed than the plate beneath them.”

“Nobody predicted that it should behave like this,” Bohr continues. “You start with something that is completely circular, basically like a hand without fingers, and, suddenly, out of nowhere, fingers develop. The fluid is pressed against a round wall, at first in a circular shape, but it wants to become something else, to develop a corner.”

Bohr finds the mystery fascinating. The circle shape demonstrates instability, but when it develops into a polygon (and Bohr’s team has found that the polygon can have anywhere from two to six sides), it becomes quite stable and can remain the same for hours. In some cases there can also be slow transitions from one polygon to another.

The findings are related to geophysical phenomena around us. Bohr explains that similar forces are at work on our own planet: “We live on a rotating sphere, and fluids abound in the oceans and in the atmosphere,” he explains. “Our experiment might help us know the basic instabilities and properties of systems like that.”

Rotating Polygons.
Rotating Polygons. Credit: Thomas Jansson.

Right now, admits Bohr, there is little known of these rotating polygons beyond the fact that they exist, and that they behave in ways nobody expected. “We think this is a spectacular phenomenon” he says, “but we don’t know why it works. Maybe someone will get a bright idea when they read our paper.”

Bohr has plans to continuing examining this phenomenon. “We want to build new containers with different sizes, et cetera, and find ways to probe this more accurately, so we can be sure exactly which conditions are necessary to see the polygons.”

You can see pictures of the experiment, and watch a video, by visiting the Technical University of Denmark’s Rotating Polygons site.

By Miranda Marquit, Copyright 2006 PhysOrg.com

Explore further: And so they beat on, flagella against the cantilever

add to favorites email to friend print save as pdf

Related Stories

A step closer to an ultra precise atomic clock

Apr 16, 2009

A clock that is so precise that it loses only a second every 300 million years - this is the result of new research in ultra cold atoms. The international collaboration is comprised of researchers from the ...

Recommended for you

Magnetic neural control with nanoparticles

6 minutes ago

Magnetic nanoparticles don't have to be "one size fits all." Instead, individual magnetic nanoparticles can be tailored in an array of differing sizes and compositions to allow for heating them separately ...

The curious case of the fluctuating speed of light

16 minutes ago

Suppose you were an electrician. You've trained, apprenticed, passed all your certifications, and you've worked with electric wiring for years. You've wired houses and commercial buildings for years, and ...

And so they beat on, flagella against the cantilever

Sep 16, 2014

A team of researchers at Boston University and Stanford University School of Medicine has developed a new model to study the motion patterns of bacteria in real time and to determine how these motions relate ...

Tandem microwave destroys hazmat, disinfects

Sep 16, 2014

Dangerous materials can be destroyed, bacteria spores can be disinfected, and information can be collected that reveals the country of origin of radiological isotopes - all of this due to a commercial microwave ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Cesar
not rated yet Jul 05, 2008
I cannot help but to think in harmonics, waves, and such...
dr_stupid
5 / 5 (1) Oct 14, 2008
This effect is now being seen in nature... see the recent Jet Propulsion Lab pics of the hexagonal storm on Saturn:

http://www.jpl.na...2007-034

I would imagine that finding a relationship between the fluid rotation speed and the bottom plate's rotation speed would then help in calculating the true rotation speed of Saturn underneath its atmosphere...