Applying alternating twists to cylindrical container found to cause dice to line up

December 7, 2017 by Bob Yirka report
Applying alternating twists to cylindrical container found to cause dice to line up
Experimental cell and sketch of the twist excitation. The pictures show the initial (left) and final (right) states for a ensemble of 25 000 cubes submitted to N = 3×105 twists of intensity Γ=1.01. Credit: Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.228002

(Phys.org)—A small team of researchers from Universidad de Navarrahas in Spain and Cinvestav Unidad Monterrey in Mexico has found that applying alternating twists to a cylinder full of square dice causes the dice to line up. In their paper published in the journal Physical Review Letters, the group describes their experiments with agitating dice and what they found.

Most people have witnessed what happens when randomly agitating a jar full of rocks, nuts or other hard objects—over a short time, they line up in a way that causes them to become more compacted. Manufacturers have learned to take advantage of this by designing machines that agitate or tap containers to compress the materials. In this new effort, the researchers report that alternating agitation does an even better job, at least with small, square objects.

In their experiments, the researchers loaded 25,000 plastic dice, each approximately a half-centimeter on a side, into a clear . They then applied different agitation effects to the cylinder to see which might cause the most effective compaction. They found that an alternating twisting, similar to that used by a common clothes washing machines worked best—but only when enough acceleration was applied. They found that the applied rotation exerted an outward force against the walls of the cylinder while the jolt that occurred when a spin motion was suddenly halted and then reversed caused the dice to shuffle slightly. Applying the alternating twisting technique caused the dice to line up top to bottom and also to form concentric circles when looked at from above.

With the angular acceleration below the threshold, the twisting oscillation does not lead to complete ordering of the dice in the center, even after a day of agitation (100,000 twists), as shown in this time-lapse video. (A logarithmic time scale is used, with identical intervals of time passing between images for 100; 1000; 10,000; and 100,000 cycles.). Credit: K. Asencio et al., Phys. Rev. Lett. (2017)

The researchers also found that for the technique to work, enough rotational acceleration had to be applied to sufficiently cause a useful amount of movement by the dice when it was suddenly halted. More specifically, they found that acceleration of approximately half that of gravity caused the dice to reach a maximum density after 10,000 alternating twists. Lower accelerations were not sufficient to cause the dice to line up in a reasonable amount of time.

The researchers suggest their findings offer a possible new means of compacting materials as part of a manufacturing processes.

Explore further: Predicting a die throw

More information: K. Asencio et al. Experimental Study of Ordering of Hard Cubes by Shearing, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.228002

ABSTRACT
We experimentally analyze the compaction dynamics of an ensemble of cubic particles submitted to a novel type of excitation. Instead of the standard tapping procedure used in granular materials we apply alternative twists to the cylindrical container. Under this agitation, the development of shear forces among the different layers of cubes leads to particle alignment. As a result, the packing fraction grows monotonically with the number of twists. If the intensity of the excitations is sufficiently large, an ordered final state is reached where the volume fraction is the densest possible compatible with the boundary condition. This ordered final state resembles the tetratic or cubatic phases observed in colloids.

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mackita
1 / 5 (1) Dec 07, 2017
This effect is example of negative time arrow in gravity field. Vibrations of certain wavelength have negentropic character, as they make particles more arranged instead of chaotic. Once this wavelength would get larger or smaller, it would have an opposite effect. On similar principle the laser cooling of atoms within boson condensates is based: its wavelength must be continuously tuned in such a way, it will always remain below energy of atom excitations.
Da Schneib
5 / 5 (1) Dec 07, 2017
This is an interesting result. It's not all that surprising considering the shape of the dice, particularly their sides' alignment. There is a bit of interesting chaos math here, and comparison with compaction of irregularly shaped polyhedra as in the sandbox method and the sandcastle problem could have important mathematical results in chaos math.
PoppaJ
1 / 5 (2) Dec 07, 2017
Yet another STUPID study posted! Some one paid these simpletons to put dice in a jar and agitate them. In the articles second paragraph is states """"Most people have witnessed what happens when randomly agitating a jar full of rocks, nuts or other hard objects—over a short time, they line up in a way that causes them to become more compacted.""""" in other words THEY LINE UP! Stop posting stupid! This was a waste of time to read. It was a waste of time experiment. It was a waste scientific effort.
FredJose
5 / 5 (1) Dec 08, 2017
@PoppaJ - seems like you've missed the whole point of the exercise - namely to QUANTIFY the forces involved to cause such compaction. Previously people had observed the effect but could not explain how or when it should occur repeatedly, i.e. under what controlled and directed conditions.
Nik_2213
not rated yet Dec 08, 2017
Some of the bulking ingredients that go into tablets must be tested for how they compact. We had an old rig with a motor and cam in the base that slowly, but repeatedly lifted then dropped a cylinder of powder or granules by about an inch. It spawned many, many 'Knock-Knock' jokes...

IIRC, when one supplier got their crystallising etc process horribly wrong, the volume *increased* as particles segregated by size...

( I still shudder at memory of how a pre-purchase sample of 'natural shellac' crawled from its opened bag and spread across the bench. Our intrepid microscopist reported an infestation of mites, even identified the little monsters... )

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