Thursday, April 09, 2015

Beaded Chains Groove to the Music

Here are a wonderful couple of videos showing beaded chains grooving to the music.

Of course in reality the chains are being shaken by a vibrating platform, but the swirling patterns and spirals that spontaneously form lends a lovely charm to an otherwise dull set of chains. In the first video, the blue and red chains seem to be engaged in an intricate and lively dance of give and take (watch in HD for the best effect). The images taken 5 seconds apart and sped up to 10 frames per second to create the video.


These videos were created by Justin Bondy, a former master's student at the University of Toronto, and his supervisor, Stephen Morris, with the aim of studying the separation of DNA strands during cell division. They hoped the two chains would create an experimental model that could shed light on how two-dimensional polymers unmix at much smaller scales.

This second video shows the red and blue chains starting out in a jumbled, mixed-up configuration and then spontaneously unmixing themselves as they jitter, an effect that Morris suggests is caused by the natural desire of a system to increase its 'disorder' or entropy.


"The rather surprising fact is that there are more configurations for which the chains are unmixed than there are for them mixed," said Morris.

The shaking table provides energy to the chains, similar to increasing the temperature, and allows the chains to find the unmixed states, which have higher entropy. This is opposite to the behavior of unchained particles, which would naturally want to be as mixed as possible.

But it's hard to prove this entropy-driven theory, either for chains or DNA strands. "There are numerical simulations and calculations of polymers in 2 and 3 dimensions which also unmix, apparently for that same reason," said Morris. "But the real chains are dissipative (have lossy collisions and friction) and so are really driven, constrained granular media — a much harder and unsolved dynamics problem"

The shaking chains also tend to form large spirals, perhaps akin to cooling and condensing into a kind of 'droplet'. But this is yet another unsolved problem.

Studying these kinds of systems could answer the question of how DNA strands unmix during the cell division of bacteria such as E Coli. "Bacteria lack all the microtubules and machinery of eukaryotic cells, so its not clear how they achieve this separation," said Morris.

Entropy could be the driving force behind both DNA unmixing and the beautiful swirling patterns of chains, but the chains' complex behavior has also raised many more questions about bouncing, constrained, granular materials.

Check out Stephen Morris' other fun physics videos on YouTube.

--
By Tamela Maciel, also known as "pendulum"

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