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Repeatedly tap on a box of marbles or sand and the pieces will pack themselves more tightly with each tap. However, the contents will only approach its maximum density after a long time and if you use a carefully crafted tapping sequence. But in new experiments with a cylinder full of dice vigorously twisted back and forth, the pieces achieved their maximum density quickly. The experiments could point to new methods to produce dense and technologically useful granular systems, even in the zero gravity environments of space missions.
Granular matter is common in nature and in industry, from the sand and gravel of the building trade to powders in foods and pharmaceutical manufacturing. Under the influence of gravity, simple vibration or tapping can make granular matter grow more compact over time, as dislodged particles find ways to fall further down with each shake. Industrial plants use this effect with powders and grains of many kinds.
Exploring other ways to pack granular matter, Diego Maza and colleagues from the University of Navarra in Spain experimented with plastic dice in an upright cylinder subjected to oscillating rotations about its vertical axis. They observed gradual packing but also found that the effects of twisting are quite different from those of tapping.
The team first poured 25,000 dice, each roughly a half centimeter on a side, into a cylindrical container. They then began twisting the container, rotating it alternately clockwise and counterclockwise about once per second and continued for several hundred thousand twists. The rotation exerted a force on the dice directed outward toward the walls, and the oscillation provided periodic jolts at the two moments during each cycle when the rotation direction reversed. The team varied the strength of these jolts by adjusting the speed of the steady rotation between reversals.
physics.aps.org
Granular matter is common in nature and in industry, from the sand and gravel of the building trade to powders in foods and pharmaceutical manufacturing. Under the influence of gravity, simple vibration or tapping can make granular matter grow more compact over time, as dislodged particles find ways to fall further down with each shake. Industrial plants use this effect with powders and grains of many kinds.
Exploring other ways to pack granular matter, Diego Maza and colleagues from the University of Navarra in Spain experimented with plastic dice in an upright cylinder subjected to oscillating rotations about its vertical axis. They observed gradual packing but also found that the effects of twisting are quite different from those of tapping.
The team first poured 25,000 dice, each roughly a half centimeter on a side, into a cylindrical container. They then began twisting the container, rotating it alternately clockwise and counterclockwise about once per second and continued for several hundred thousand twists. The rotation exerted a force on the dice directed outward toward the walls, and the oscillation provided periodic jolts at the two moments during each cycle when the rotation direction reversed. The team varied the strength of these jolts by adjusting the speed of the steady rotation between reversals.
Dice Become Ordered When Stirred, Not Shaken
A jumble of thousands of cubic dice, agitated by an oscillating rotation, can rapidly become completely ordered, a result that is hard to produce with more conventional shaking.
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