Glass beads cluster as they flow
June 29, 2009 6:04 PM   Subscribe


Really pretty.

Science people, what could be the attractive force between these little bits of silica that causes this behavior?
posted by leotrotsky at 6:23 PM on June 29, 2009

Static electricity? I hope not, since that is not very interesting.
posted by Stonestock Relentless at 6:27 PM on June 29, 2009

Minimization of surface energy, just like liquids? Note that it isn't just liquids that have surface energy--it also (in part) governs things like crack propagation in a solid body, where new surface has to be created. Pulling one large crystal apart may be at least comparable in quality, if not in quantity, to pulling two sand grains from each other.

And now that I read the article, I see they say exactly that. So...I'm so smart I don't even need to read the links anymore!
posted by DU at 6:32 PM on June 29, 2009 [1 favorite]

Plateau-Rayleigh instability?

I've only got time to skim the articles at the moment, but this is an awesome principle that despite my knowing about I am shameful to admit I haven't much looked into it.

Quartz (which is silica - SiO2 - which is glass - and which makes up any pure sand), I've noticed, tends to display a lot static electricity behavior in the lab. I've wondered if it has anything to do with the piezoelectricity effect but, not being a physicist and not having the time to devote to it, I've mostly gotten lost in the details.

At any rate, solid or semi-solid materials can display some awesome behaviors. My favorite is probably thixotropy (full disclosure: this is a colleague of mine), typically in fine-grained sediments. Salt, also, is known to flow, sometimes catastrophically, under pressure. This is one of the arguments against using Yucca Mountain as a nuclear waste dump; there are concerns some underlying salt layers could activate, triggered by something like an earthquake, which would not be all too good. These are more than likely totally different processes, but I still think they are awesome.
posted by six-or-six-thirty at 6:36 PM on June 29, 2009

Remember too that air is a component of sand, and is itself a (compressible) fluid. I am sure that it contributes to the behavior of the sand significantly in these videos.

There is some electrical attraction in the sand particles as well, as six-or-six-thirty points out. It can be really clingy, staticky stuff when it's really dry.

Be interesting to see this done in a vacuum. Water would just vaporize instantly, but the sand would not.
posted by Xoebe at 7:00 PM on June 29, 2009 [3 favorites]

Um, by air, I mean of course the air in between the sand particles.
posted by Xoebe at 7:01 PM on June 29, 2009

Of course they do.

I am mystified that this is such a, well, mystery. The articles admit that the forces are "very small," thus perhaps explaining why they had to drop their camera to record the phenomenon. The thing is, silica is EXTREMELY non-conductive, and therefore conducive to picking up charges and holding on to them for lots of trivial reasons. Most of those reasons involve friction, and in this experiment the stuff was being what poured from a beaker or something? Lots of friction there.

So these non-conductive particles with random charges deposited on them and kind of hanging on there are now in free fall. Does it surprise anybody that they might align with opposite charges attracting?
posted by localroger at 7:03 PM on June 29, 2009

And yeah, they called it interstitial gas in the last link...interesting though, I was not familiar with the Brazil Nut effect. Great name!

This could help explain why rocks come to the surface in soil. Freeze thaw cycles, for example, impart energy to the soil, and the Brazil Nut effect is what makes them rise rather than sink.

That's why they make so many rock walls in Ireland. Gotta pick up the damn rocks every spring and do something with them.
posted by Xoebe at 7:07 PM on June 29, 2009

Of course they do. . . . Does it surprise anybody that they might align with opposite charges attracting?

Why does it have to be a surprise? Why can't it just be something interesting and neat to look at?
posted by brain_drain at 7:13 PM on June 29, 2009

i guess i'm in the minority here. i think the phenomenon is interesting, but i was hoping it would look cooler. still, good to know!
posted by snofoam at 7:20 PM on June 29, 2009

I thought this was old news... Go to this video from 1984 and at 3:19 in the bottom left of the screen, sand substitutes for water because water doesn't miniaturize: Film
posted by CarlRossi at 9:35 PM on June 29, 2009

Maybe they're drafting.
posted by weapons-grade pandemonium at 10:08 PM on June 29, 2009

Be interesting to see this done in a vacuum. then we would watch the Van Der Waal's force in freefall.
posted by hortense at 10:31 PM on June 29, 2009

panta rhei kai ouden menei
posted by Substrata at 1:16 AM on June 30, 2009

This is excellent. Somehow, when we think we understand pretty much everything, it turns out we dont even really get sand yet.
posted by Capt Jingo at 7:37 AM on June 30, 2009

Static electricity? I hope not, since that is not very interesting.

On the contrary, I think subtle and pervasive electromagnetism may explain many mysteries in the world--from the micro to the macro.

It's always exciting when physicists are surprised. Any day now, someone could have a "duh!" moment which suddenly explains dark matter, or dark energy, or inflation based on something as prosaic as electromagnetic fields.

posted by General Tonic at 8:00 AM on June 30, 2009

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