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Researchers Discover That Sand Behaves Like Water

Soulskill posted more than 5 years ago | from the not-in-your-stomach dept.

Science 192

Xeger writes "University of Chicago researchers have found that streams of sand can behave in a similar manner to liquids, forming water-like droplets when poured from a funnel. To obtain these results, they dropped their expensive high-speed camera from a height of several meters and observed the sand forming into droplets — something that shouldn't happen without surface tension. These findings suggest that conventional engineering wisdom about sand, dirt and other grainy materials needs to be rethought, and that it might be possible to apply fluid dynamics to some solids problems."

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Lol (2, Funny)

Anonymous Coward | more than 5 years ago | (#28494259)

Quicksand discovered !!!

Not quicksand (4, Informative)

rlseaman (1420667) | more than 5 years ago | (#28495001)

Quicksand discovered !!!

Quicksand is rather a colloidal suspension requiring an underground water source:

http://en.wikipedia.org/wiki/Quicksand [wikipedia.org]

Re:Not quicksand (2, Informative)

Quothz (683368) | more than 5 years ago | (#28495117)

Quicksand is rather a colloidal suspension requiring an underground water source

Not necessarily [wikipedia.org] .

Re:Not quicksand (3, Interesting)

Ozlanthos (1172125) | more than 5 years ago | (#28495261)

Up here in the northwest, we have what we call "quick-mud". It is worse than quicksand in some ways, but fortunately it usually only occus in cauldrons just large enough to suck your leg in up to your crotch. Which means half of your lower half is now wet/muddy and you have most likely lost your shoe as well.

-Oz

hmm... (5, Interesting)

Anonymous Coward | more than 5 years ago | (#28494283)

That's peculiar. What's binding the grains together to that extent? Moisture? Electrostatic charge? Just chance mechanical interactions of surface asperities? The first and last are already modelled in some engineering sand models, but I'm not sure they'd be powerful enough to cause droplet formation.

Re:hmm... (-1)

Anonymous Coward | more than 5 years ago | (#28494301)

Uh, gravity?

Re:hmm... (-1, Troll)

Anonymous Coward | more than 5 years ago | (#28494573)

Whomever modded that overrated is a faggot.

There is a female jazz bassist who keeps time by talking to herself while she plays. She says "annnnnd....nigsandchinksandkikesandspicsandnigsandchinksandkikesandspics..."

Oddly enough, she makes love to this [lakersuniverse.com] man. But that means that she is a heterosexual and not a homosexual like the guy who modded that overrated.

Re:hmm... (2, Interesting)

Anonymous Coward | more than 5 years ago | (#28494339)

I say it's air. In the places where the stream was thinnest, turbulence began to push the sand toward the thicker sections until it formed blobs. The water will stay in droplet form once it stops moving, but the sand will fall apart without moving air acting against it.

Re:hmm... (1, Insightful)

Anonymous Coward | more than 5 years ago | (#28494621)

After posting the Parent, it occurred to me that it could also be thought of in terms of the low-pressure column that is created as something falls through the air. Perhaps this is better explained in terms of the air pushing its way into the column at its less dense points.

Signed,
Anonymous Cowardon

Re:hmm... (0)

clintp (5169) | more than 5 years ago | (#28494697)

I'm with you on this one. Occam is too.

It seems like the researchers are overreaching a bit here for a complex explanation, when a simpler one will do nicely.

Re:hmm... (5, Informative)

JustinOpinion (1246824) | more than 5 years ago | (#28494835)

The researchers did consider the effect of air. In fact, the ambient air has the opposite effect: the drag of the air as the droplets fall rips grains out of the droplets, thus working against whatever effect is aggregating them. In particular the authors say in their article [doi.org] (p. 1111):

For a rough estimate of the cohesive strength we track clusters as they fall and accelerate to a speed at which Stokes drag pulls individual grains off cluster protrusions. Correcting for slight changes in the air viscosity at reduced pressure, this gives values of a few nanoNewtons.

They then go on to measure more careful the strength of the clustering force, and ascribe it to both Van der Waals interaction and capillary forces. They did perform the experiment as a function of humidity to test the effect of water bridging (capillary forces) and found it to be significant. But they provide further data suggesting that Van der Waals forces also play a role. Again from the article (p. 1112):

It is difficult to distinguish van der Waals from capillary forces because we cannot rule out molecularly thin absorbed films that create tiny bridges between individual asperities24,25. However, we still observe clustering in glass grains stored under vacuum (0.05 kPa) at low humidity (,1%) and also in grains coated with hydrophobic silane.

The fact that clustering still occurs in vacuum suggests air is not crucial to the effect. The precise scaling they observe (e.g. the size and separation of the clusters as a function of time) is not consistent with simple inelastic collisions, and the effect of air would actually be to breakup the droplets, absent any attractive force. What they instead measured was a weak (but sufficient!) interaction between grains, which they ascribe to surface forces and capillary action.

Re:hmm... (1)

eyepeepackets (33477) | more than 5 years ago | (#28495371)

"Go pound air!" doesn't have the same ummph to it.

"Go pound sand with air!" has promise.

"Go pound sand with water!" is kinda kinky.

Re:hmm... (1, Interesting)

Anonymous Coward | more than 5 years ago | (#28494379)

TFA says "The droplets formed because of instabilities in the subtle atomic forces that attract sand grains to each other."

Personally I'm thinking that the air flow around a falling object might have a concentrating effect. I hope they redo their experiments in vacuum to be sure.

Re:hmm... (0)

Anonymous Coward | more than 5 years ago | (#28494905)

They uh, already did. Read the article.

Re:hmm... (1)

Daniel_Staal (609844) | more than 5 years ago | (#28495245)

They did.

Re:hmm... (0)

Anonymous Coward | more than 5 years ago | (#28494489)

The experiments were, in fact, performed under a reasonably strong vacuum.

Re:hmm... (0)

Anonymous Coward | more than 5 years ago | (#28494533)

I didn't see that in the article, and the video doesn't seem to support it. All matter should fall at the same rate in a vacuum, yet loose granules of sand can be seen falling slower than the blobs.

Re:hmm... Gravity!! (1)

MoToMo (17253) | more than 5 years ago | (#28494633)

Gravity! It's working on a small scale, but that's why it would do that. As a casual observer, i'm pretty sure i've noticed this type of behavior in sand before, it's surprising to me that others haven't. I'm pretty sure that's the same reason why the last few cheerios stick together in the bowl of milk.

Re:hmm... Gravity!! (3, Interesting)

AnonGCB (1398517) | more than 5 years ago | (#28494715)

That's not gravity, on these scales it's not quite powerful enough. What you're thinking of is surface tension and the miniscus' formed by the cereal bits. It's actually not that bad of an example of gravity because it is a physical representation of spacetime and something denting it, which is a familiar image if you study physics to any level. I'm not sure what causes this but it obviously is going to have some interesting ramifications.

Re:hmm... (1)

clyde_cadiddlehopper (1052112) | more than 5 years ago | (#28494669)

Aerodynamics, perhaps. In the first video, we clearly see small "droplets" falling more slowly than larger blobs, indicating the sand is not falling in a vacuum. The minimum energy state for a trail of non-spherical particles could easily be a series of ovoid blobs whose shape is carved out by turbulence in the airstream.

Re:hmm... (0)

Anonymous Coward | more than 5 years ago | (#28495413)

I'll join the anonymous cowardon brigade and let you know that if you read the article results were duplicated in a vacuum. Thanks for playing!

What about the air? (0, Redundant)

White Flame (1074973) | more than 5 years ago | (#28494711)

As sand falls, it would push air molecules around, causing minor pockets of slightly higher & lower air pressure. I have no clue what sort of contribution that would be, and expect to be schooled by people much more informed in this matter than myself in the subsequent replies.

Re:What about the air? (0, Redundant)

Timmmm (636430) | more than 5 years ago | (#28494869)

Air gets my vote too. It would be interesting if they could do the experiment again in a vacuum.

Re:What about the air? (0)

Anonymous Coward | more than 5 years ago | (#28494899)

If you had read the article you would have realized they did do this!

Re:What about the air? (0)

Anonymous Coward | more than 5 years ago | (#28495111)

It would be interesting if they could do the experiment again in a vacuum.

But apparently not quite interesting enough to get you to, oh, ya know, read the article 'n stuff.

Re:What about the air? (1)

confused one (671304) | more than 5 years ago | (#28495251)

They did and the results were the same.

Re:hmm... (4, Informative)

JustinOpinion (1246824) | more than 5 years ago | (#28494729)

For those with access, the actual scientific article is:
John R. Royer, Daniel J. Evans, Loreto Oyarte, Qiti Guo, Eliot Kapit, Matthias E. MÃbius, Scott R. Waitukaitis & Heinrich M. Jaeger "High-speed tracking of rupture and clustering in freely falling granular streams [nature.com] " Nature, 459, 1110-1113 (25 June 2009) | doi:10.1038/nature08115 [doi.org] .

The associated "News and Views" (Summary) is:
Detlef Lohse & Devaraj van der Meer "Granular media: Structures in sand streams [nature.com] " Nature, 459, 1064-1065 (25 June 2009) | doi:10.1038/4591064a [doi.org]

The previously-held belief in the field was that this breakup into droplets could be explained by inelastic collisions between the grains. That is, all the sand grains are bouncing off each other, but because these collisions are inelastic (the two particles slow down a bit relative to each other with the collision) the grains will, statistically, aggregate into larger structures.

However this new piece of work shows rather strikingly that the origin of the force is a very weak form of surface tension. In other words, the breakup into droplets occurs for the same reason as it does in water and other liquids... it's just the magnitude of the force that is much smaller. In addition to the high-speed photography the Slashdot summary mentions, they also used atomic force microscopy [wikipedia.org] to directly measure the nanometer-scale cohesive forces between particles. In water, surface tension arises from the (rather strong) cohesive forces between water molecules (each water molecule 'sticks' to its neighbors). In sand, it appears that a very weak nano-scale cohesive force is nevertheless enough to generate macro-scale droplets out of micro-scale particles. The cohesive forces in sand arise from the weak Van der Waals [wikipedia.org] forces (weak, but universal, surface attraction), and due to capillary forces. That is, ambient water bridges the sand particles and causes what is effectively an attractive force, which leads to an effective surface tension.

In the paper, they describe how they vary the particle type and ambient conditions, to demonstrate that these two effects are important. For instance varying humidity alters the cohesion and thus droplet formation. Also, altering the sand particles has an effect: e.g. rougher particles cannot stick to each other as much, thereby reducing this effect.

This is a neat piece of work because it involves just "known" physics. It is demonstrating that well-established physical effects (surface forces and capillary forces) can explain phenomena where their effect was previously assumed to be negligible. The surface tension in these granular media are about 100,000 times smaller than water, yet the exact same effects are observed: the surface tension, weak as it is, tries to minimize surface area. Coupled with well-known instabilities [wikipedia.org] , this causes a breakup into droplets.

Re:hmm... (1)

Directrix1 (157787) | more than 5 years ago | (#28494879)

Gravity?

Re:hmm... (0)

Anonymous Coward | more than 5 years ago | (#28494967)

That was exactly the first comment on this post and it was modded down. Good luck using reason and logic.

They dropped their expensive camera? (3, Insightful)

hey! (33014) | more than 5 years ago | (#28494297)

Haven't they heard of strobe lights?

Re:They dropped their expensive camera? (5, Funny)

BadAnalogyGuy (945258) | more than 5 years ago | (#28494423)

Besides that, there is also the problem of the greater weight of the camera causing it to fall faster than the lighter grains of sand. Ideally, you'd want to observe the sand in as stationary and synchronized a manner as possible. However, if the camera is moving relative to the sand, it would be difficult to monitor any particular clump of falling sand.

Re:They dropped their expensive camera? (5, Informative)

samriel (1456543) | more than 5 years ago | (#28494467)

Besides that, there is also the problem of the greater weight of the camera causing it to fall faster than the lighter grains of sand. Ideally, you'd want to observe the sand in as stationary and synchronized a manner as possible. However, if the camera is moving relative to the sand, it would be difficult to monitor any particular clump of falling sand.

I have one word to say to you and just one word: Galileo. [jimloy.com]

Re:They dropped their expensive camera? (2, Interesting)

Nursie (632944) | more than 5 years ago | (#28494581)

Whilst he does explain it ass-backward, you would anticipate a greater resistive effect from thee air on multiple smal grains of sannd, with a proportionally large surface area, wouldn't you?

But yeah, the statement as it stands is bullcrap.

Re:They dropped their expensive camera? (1)

ae1294 (1547521) | more than 5 years ago | (#28494675)

Whilst he does explain it ass-backward,

Sorry I'd have to agree with the grand-parent as I busted out laughing when I saw weight equals falling faster espically since the first few post where all nerdy....

But here's a question. When does something changing from a liquid to a solid change models? Donno might be just as stupid as the above but I think it's interesting that sand can exist in several different states including a liquid.

Re:They dropped their expensive camera? (1)

Naerymdan (870497) | more than 5 years ago | (#28494859)

I would venture to say that sand grains behaved like a liquid, not became a liquid.

Re:They dropped their expensive camera? (1)

ae1294 (1547521) | more than 5 years ago | (#28494907)

What? NO..

I think you missed what I was saying. You know, when you heat sand, it melts into a liquid. Reading this thread made me wonder about all the little rules that govern how liquids behave vs how solids behave and what happens in the in-between states and how that relates to this.

But never mind I wasn't expecting the Spanish Inquisition this morning.

Re:They dropped their expensive camera? (0)

Anonymous Coward | more than 5 years ago | (#28495079)

When does something changing from a liquid to a solid change models?

Never? Aren't liquids just a bunch of solid particles as well? Sure they are smaller but on an abstract level, where's the difference? Is there any? I propose that the transition is fluid (Get it? Fluid! Ahahahaha! Never mind.).

Re:They dropped their expensive camera? (1)

ae1294 (1547521) | more than 5 years ago | (#28495227)

Sure they are smaller but on an abstract level, where's the difference? Is there any?

Ummm I have no education in the question at hand but I believe solids are at a lower energy state for any given substance. Liquids have more energy and gasses have much more and thus are all bouncy and shit. I just totally fsked my explanation up in many different ways.. Maybe I should have googled "phase change" or something but that's a lot of work and I just wanted someone to give me the answer because I'm Cowboy Neal's half brother twice removed.

NOW STOP MAKING FUN OF ME DAMN IT.... I'm an American and I'll SUE your ass...

Re:They dropped their expensive camera? (1)

Quothz (683368) | more than 5 years ago | (#28495255)

Never? Aren't liquids just a bunch of solid particles as well? Sure they are smaller but on an abstract level, where's the difference? Is there any?

I'm not a physicist, so I dunno what I'm talking about, but I don't think so, no. Calling molecules of liquid "solids" doesn't sound right to me, since at a low level we see zero-mass charged particles and lots of empty space. Matter in different states can have wildly different properties. The difference is the state of excitation of the molecules or atoms.

Re:They dropped their expensive camera? (1)

tsstahl (812393) | more than 5 years ago | (#28495313)

When does something changing from a liquid to a solid change models?

When light wavicles hit it?

*rimshot*

Re:They dropped their expensive camera? (1)

Scrameustache (459504) | more than 5 years ago | (#28495023)

anticipate a greater resistive effect from thee air on multiple smal grains of sannd

For someone making so much sense, you sure type like a retard :)

Re:They dropped their expensive camera? (2, Interesting)

hey! (33014) | more than 5 years ago | (#28494805)

I have seven words to say to you: no we will not let you go!

Re:They dropped their expensive camera? (1)

Quothz (683368) | more than 5 years ago | (#28495193)

I have one word to say to you and just one word: Galileo. [jimloy.com]

You might consider reading the article you linked. Galileo was closer to the mark than Aristotle but not fully correct. As it points out, a more massive object does accelerate more quickly in a vacuum. Outside of a vacuum, a larger object encounters more friction and accelerates more slowly. Mind you, both effects are infinitesimally small in terms of this experiment; as usual, BaG's point is worth a moment's thought but fails to apply to the issue at hand.

Re:They dropped their expensive camera? (1)

ae1294 (1547521) | more than 5 years ago | (#28495357)

m. Outside of a vacuum, a larger object encounters more friction and accelerates more slowly.

Damnit.. Didn't I watch a video of a guy on the moon test this with a golf ball and a feather and they both hit the (moon) ground at the same time?

Fuck this... I'm going back to bed...

Re:They dropped their expensive camera? (0)

Anonymous Coward | more than 5 years ago | (#28494495)

The camera is slowly moving relative to the sand, but it is not difficult to monitor any particular clump of falling sand. Go watch the video, armchair critic. Besides, the formula for speed due to gravity (1/2*g*t^2) doesn't depend on the mass of the object falling.

Re:They dropped their expensive camera? (0)

Anonymous Coward | more than 5 years ago | (#28494753)

It is not the mass, but the cost of the camera that determines the terminal velocity. Nature always tries to maximize the amount of damages.

Re:They dropped their expensive camera? (0)

Anonymous Coward | more than 5 years ago | (#28495017)

for fuck's sake, scientology even screws up your basic physics knowledge? I thought it only targeted psychology.

Re:They dropped their expensive camera? (0)

Anonymous Coward | more than 5 years ago | (#28495163)

At first, I thought of modding you down but them I noticed your /. username. Sarcasm isn't always very obvious, considering the pool of stupidity we live in. ~

Re:They dropped their expensive camera? (0)

Anonymous Coward | more than 5 years ago | (#28495351)

There is no analogy involved, feel free to down-mod him.

Re:They dropped their expensive camera? (1)

Jstlook (1193309) | more than 5 years ago | (#28495387)

Besides that, there is also the problem of the greater weight of the camera causing it to fall faster than the lighter grains of sand.

Observe! You'd think this ball *produces cannonball* would fall faster than this feather *produces feather*.
*performs experiment*
And .. you'd be exactly right. -- Rosencrantz (or is it Guildenstern?)

I knew a prof that did that! (dropped a camera) (1)

StCredZero (169093) | more than 5 years ago | (#28494583)

He was a film prof, not physics, however. He rigged up a pulley system, so you could film a Point Of View sequence for someone thrown down a stairwell. The friction from the rope and pulley would slow down the acceleration and fall, but the camera could be run at a slower speed to compensate. At the last moment, you could grab onto the rope (with thick gloves) and save the camera. A bit of spin and/or off-center mounting of the camera would give you a more chaotic feel.

Effective and cheap.

Re:They dropped their expensive camera? (1)

complete loony (663508) | more than 5 years ago | (#28495007)

Just send a small transparant container of sand on the vomit comit or a space shuttle...

Mars (5, Interesting)

Cryin'Red (915212) | more than 5 years ago | (#28494305)

Interesting.... I've always wondered how those Martian erosion patterns could definitively be ascribed to surface water, perhaps they will have to rethink that now?

Re:Mars (1)

sleeponthemic (1253494) | more than 5 years ago | (#28494693)

Surely this research would be most applicable in very small scale scenarios?

Re:Mars (1)

JustinOpinion (1246824) | more than 5 years ago | (#28495035)

The effect as described in the scientific paper relies on van der Waals interaction and also capillary forces. In other words, a significant portion of the force/effect comes from ambient water that coats the particle surfaces, and creates adhesion by bridging between particles when they touch.

So this suggests that sand will act most "liquid-like" (breaking into droplets, flowing, etc.) when there is atmospheric water.

I agree that this kind of data on granular media will have an effect on the interpretation of Mars erosion patterns. But I think it would be simplistic to say that this offers a non-water explanation for the erosion patterns on Mars. In fact it may be further evidence of water and help determine exactly how much water Mars currently has, and previously had. (It's also worth noting that the erosion patterns are now just one of many pieces of evidence we have for there being water on Mars.)

Knudsden number (3, Interesting)

Richard Kirk (535523) | more than 5 years ago | (#28495187)

We see a stream of sand dividing up into 'drops'. It has been suggested that these 'drops' of sand are not being held together by internal forces, but by the air currents. The sand is arranging itself into shapes that can fall through the air, and horizontal oscillations of the air may be causing the column to break up into these 'drops'. I am not sure that is wholly the case - the video shows an intriguing 'satellite' droplet after a main one, a lot like you get with liquids.

So, could you get the same effect on Mars? You have less than 1/100th of the pressure, so we might expect the forces from the air to be proportionately weaker. There is also a characteristic length - the mean free path - which is the distance an atmospheric particle will travel before it hits another. If the geometry of what we are looking at - in this case, the sand - goes beneath the mean free path, then the flow changes. There is a dimensionless number called the Knudsden number which describes the point in which this change occurs. The man free path in the earth's atmosphere is about 0.1 micron, so on Mars it will be about 10 microns, which is probably still smaller than sand, so the Knudsden number is still below 1.0. My guess is you may get these 'droplets' on mars, but the effect is a lot weaker ad you would need a much longer drop for the effect to show itself. I hope the people repeat the experiment under vacuum. If you still get the effect in vacuum, then it must be something else.

Powders can behave a lot like liquids provided they keep moving. They can leave tracks that look a lot like liquids. I suspect some of the things we see on Mars may have been formed by powders. However, most of these mechanisms are particles moving over each other under the influence of gravity, and don't really use the atmosphere as the sand may be doing here. However, I started off as a major sceptic on water on Mars, but the evidence of shorelines (which you wouldn't get with powders unless there was something to keep them moving) is beginning to win me over. We shall see.

Here's my usual pet peeve with journalism like this. The motion of powders is a fascinating topic, and it doesn't really need dressing up as the 5th state of matter that baffles scientists. It is not a forgotten topic in science. Fluidized beds are used in industrial chemistry. They tend to be a bit unpredictable, because when they slump, it can be very hard to get them going again, which is what makes them unpredictable.

Water on Mars? (2, Funny)

koan (80826) | more than 5 years ago | (#28494321)

The finer the sand the more it acts like this, that's your "water on mars" right there.

Re:Water on Mars? (3, Interesting)

mrsquid0 (1335303) | more than 5 years ago | (#28494507)

The evidence for water on Mars is stronger than just erosion features. There is chemical evidence as well. Still, this does call into question how wide-spread the water was in the highland areas.

Re:Water on Mars? (1)

Nefarious Wheel (628136) | more than 5 years ago | (#28494509)

The finer the sand the more it acts like this, that's your "water on mars" right there.

A good example of that would have been observed by anyone changing the toner in one of the old high-end HP colour laser printers. You could see the highly liquid nature of the fine grain toner through the translucent plastic cartridges. That stuff sloshes.

Re:Water on Mars? (0)

Anonymous Coward | more than 5 years ago | (#28495143)

You realize toner is suspended in a liquid, right

Meh... (1)

Bin_jammin (684517) | more than 5 years ago | (#28494327)

It's probably just due to static electricity.

Re:Meh... (4, Informative)

JustinOpinion (1246824) | more than 5 years ago | (#28494943)

Nope. The researchers thought of that, too. But they ruled-out electrostatic charging. From the article [doi.org] (p. 1111):

In principle, cohesion might arise from a variety of sources, including electrostatic charging, capillary or van der Waals forces. ... a rough estimate of the cohesive strength ... gives values of a few nanoNewtons. To compare this to any electrostatic forces present, we obtain the distribution of charges on the grains by applying a uniform electric field perpendicular to the falling stream and tracking individual grain trajectories (see Supplementary Information). For both glass and copper, we find the streams are neutral overall but contain a small fraction of positively and negatively charged grains, up to a roughly q_max = +/- 100,000 electron charges per grain (Supplementary Fig. S2). Still, this gives attractive electrostatic forces a maximum F_max = (1/4*pi*e_0)q_max^2/d^2 ~= 0.1 nN for grains with diameter d = 100 micrometer, too weak to be the dominant cohesive force. (Here e_0 = 8.85 * 10^-12 C^2 N^-1 m^-2 is the permittivity of free space.) Furthermore, experiments with conductive, silver-coated 100-micrometer-diameter glass spheres produce clusters identical to experiments using uncoated spheres, emphasizing that electrostatic forces do not drive the observed clustering.

(Note that I rewrote the equations in plaintext since Slashdot doesn't support all the necessary characters.)

Re:Meh... (4, Funny)

Bin_jammin (684517) | more than 5 years ago | (#28495089)

It's Saturday, I was told there would be no maths.

It's the air. (3, Insightful)

vettemph (540399) | more than 5 years ago | (#28494333)

Maybe this tells us more about what the air is doing than what the sand is doing. Chaotic particles spiraling down end up it in each others draft and stay there. (think nascar drafting)

Re:It's the air. (1)

gTsiros (205624) | more than 5 years ago | (#28494519)

that's what i thought too...

repeating the test in a vacuum would test this hypothesis pretty easily.

Re:It's the air. (5, Informative)

vux984 (928602) | more than 5 years ago | (#28495087)

repeating the test in a vacuum would test this hypothesis pretty easily.

And if you'd read the full article you'd know that they did test in a vacuum. And they still formed droplets.

Re:It's the air. (2, Funny)

The Living Fractal (162153) | more than 5 years ago | (#28494615)

That may have been the only time I've seen Nascar related to anything remotely intelligent. I applaud you sir.

Re:It's the air. (1)

sleeponthemic (1253494) | more than 5 years ago | (#28494731)

You've obviously never been to a Nascar Theoretical Physics Society meeting - they've been dropping the hammer on science for decades.

Re:It's the air. (1)

NuclearError (1256172) | more than 5 years ago | (#28495293)

He made a car analogy. Big deal!

Re:It's the air. (0)

Anonymous Coward | more than 5 years ago | (#28494845)

According to the publication itself, they've done these experiments in pressures down to 0.03 kPa and have found that "grain-gas interactions" aren't a dominant factor.

News at 10 (2, Funny)

auric_dude (610172) | more than 5 years ago | (#28494367)

Is a camel still the ship of the desert?

This is called granular flows (5, Interesting)

Saba (308071) | more than 5 years ago | (#28494375)

Sand belongs to a group of things called granular media. This includes things like pellets, ores, polymers, etc.

We typically regard the size of the particles to be larger than 1Âm. Any smaller and you have to start to take into account interparticle forces such as electrostatics and Van der Waals.

Trying to work out exactly how granular media behaves is tricky. Sometimes it behaves like a solid (sand on a beach, say -- you don't sink into it) and sometimes it behaves like a fluid (you can pour the grains of sand from a beach through your fingers). The example given here shows how it can behave inbetween solid objects (mechanics) and liquids (fluid dynamics). There's a large body of statistical and simulation results that try to understand what's going on, but nothing exists like Navier-Stokes does for liquids.

There's a lot of strange and unintuitive behaviour that arises out from studying these sorts of materials, and it's *extremely* important to industry. For example how granular media has a self-sorting behaviour when you subtly vary the size or mass of each particle.

The article shows another example of it.

Doh! (1, Troll)

Toad-san (64810) | more than 5 years ago | (#28494387)

What? Someone let the physicists out of their labs?

This has been intuitively obvious for _my_ entire life; and they just get around to noticing?

Sand hell. Watch the films of some massive landslides (including boulders weighing hundreds of tons). They're just as fluidic as they can be ... and damn-all static attraction too.

Re:Doh! (1)

russotto (537200) | more than 5 years ago | (#28494513)

This has been intuitively obvious for _my_ entire life; and they just get around to noticing?

No, the Slashdot editors just got around to noticing. Make more sense now?

"Ugly bags of mostly water" are we? (0)

Anonymous Coward | more than 5 years ago | (#28494399)

The next time a crystalline life form insults me [wikipedia.org] I'll play the kindergarten card and say "I know you are but what am I."

The Falling Sand Game (4, Funny)

SomeGuyFromCA (197979) | more than 5 years ago | (#28494403)

Huh. /Someone/ has been playing too much of that nifty little toy The Falling Sand Game [fallingsandgame.com] and calling it research.

Gotta love it (1)

zoomshorts (137587) | more than 5 years ago | (#28494419)

My karma sucks, yet I got an early post in. Yes, quicksand has been re-discovered.
Wow, plus my karmic debt transcends almost anything. What goes around aggregates
around me, much like the sand described in the article. Bonus!

5th State, Probably Not (1)

lcreech (1491) | more than 5 years ago | (#28494429)

Water or anything flowing through air develops a charge. I'm sure sand does too Relative to each other there can be a some with more some with less that would have a tendency for them to group and form droplets

So about those "rivers" and "lakes" on mars (2, Insightful)

RichMan (8097) | more than 5 years ago | (#28494453)

If sand can flow like water then perhaps the lakes and rivers shown by "water" like flow on mars were just created by sand flow.

more likely (0)

Anonymous Coward | more than 5 years ago | (#28494457)

They are making it up to explain to their boss why they need a new camera after accidently dropping it off of the roof. No explanation given as to why they choose a roof that just happen to be facing to womens dormitory shower room....

Yawn (3, Funny)

sleeponthemic (1253494) | more than 5 years ago | (#28494461)

Call me when they can run linux on sand.

(Edit: Please note phone is off, due to slashdotting)

Re:Yawn (1, Informative)

Anonymous Coward | more than 5 years ago | (#28494619)

Technically, aren't most processors running linux just baked sand?

Re:Yawn (0)

Anonymous Coward | more than 5 years ago | (#28494735)

I assumed that was the point of the joke.

Re:Yawn (1)

confused one (671304) | more than 5 years ago | (#28495291)

since microprocessors are made of silicon... it already does.

FX guys have known this for decades. (0)

Anonymous Coward | more than 5 years ago | (#28494549)

They have used sand to mimic water in miniature, that is for sets built to scale (think Godzilla), since that 1960's at least. Good to know current American science is only 50 years behind the trades and craftsmen of Hollywood.

Cool. (1)

Rik Rohl (1399705) | more than 5 years ago | (#28494551)

Gotta say, the Vid is very cool - Especially if you're stoned :P

Pour sand in a vacuum (1, Redundant)

Baldrson (78598) | more than 5 years ago | (#28494553)

The video shows sand droplets forming but some of the smaller droplets are falling more slowly than the larger droplets. This indicates the drop column has air in it.

Evacuate and try it again...

Re:Pour sand in a vacuum (2, Informative)

nloop (665733) | more than 5 years ago | (#28495267)

I thought the same thing, however, someone earlier posted a link to the original [doi.org] article, that requires a subscription to actually read, where apparently they say they tried it in a vacuum and achieved the same results

Octave Engine (1)

LunarEffect (1309467) | more than 5 years ago | (#28494613)

Hasn't this pretty much already been used in a physics engine? The Octave Engine [youtube.com] , for instance, can simulate quite a few different small particle system with very similar results.

!News (3, Insightful)

Thelasko (1196535) | more than 5 years ago | (#28494685)

Okay, maybe the sand forming droplets is news. However, my old college roommate is a structural engineer. On more than one occasion he told me that structural engineers consider soil to be a highly viscous fluid.

For example, most houses are built to "float" in the soil like a boat. For structures that won't "float", like skyscrapers, they have to drive piles down to bedrock.

isn't that obvious... (0)

Anonymous Coward | more than 5 years ago | (#28494727)

...I thought of sand behaving like water when I first saw sand dunes and wavelike patterns in desert sand when I was a little kid.

Sandworms (1)

killeena (794394) | more than 5 years ago | (#28494739)

Well, that makes things easier for sandworms.

who ya gonna call? (5, Interesting)

JackSpratts (660957) | more than 5 years ago | (#28494811)

physicists may have just figured this out but special effects guys have known about it for decades. 25 years ago in ghostbusters when the stay puft marshmallow man panic causes a fire hydrant to fail (in miniature), the fountain of "water" shooting out of it is actually diatomaceous earth. shot from above in high speed it looks amazingly real.

Re:who ya gonna call? (4, Informative)

Anonymous Coward | more than 5 years ago | (#28495133)

physicists may have just figured this out but special effects guys have known about it for decades.

With all due respect to special effects guys, they were aware of the phenomenon, but had no explanation. Physicists have also been aware of the phenomenon for decades. What this new work does is provide an explanation. From an explanation we can then move to understanding nature and rationally building technologies based on the knowledge.

Again, props to the FX people for coming up with such cool solutions. But your comment makes it seem like all that is necessary is observation. Science is about much, much more. It is about reproducible observation, experimentation, modeling, explanation, theory, and understanding.

This is interesting (1)

Dunbal (464142) | more than 5 years ago | (#28494813)

So the "surface tension" in the sand is probably due to either friction of grains of sand rubbing together, or gravity. I doubt that it's due to charge (as in water), and I'd put my money on friction.

Re:This is interesting (1)

confused one (671304) | more than 5 years ago | (#28495337)

friction creates heat, which would tend to drive them apart. Unless you're talking about air; and, they found the same effect occurs in a vacuum. As to gravity... Force due to electric charge is like 36 orders of magnitude stronger than gravity. So, if there's any chance it's electric charge, then that's the most likely reason.

Bah (0)

Anonymous Coward | more than 5 years ago | (#28494893)

Air is being pushed around the outside of the larger masses, causing the grains to coagulate into "drops".

By by wet Mars! (1)

tjstork (137384) | more than 5 years ago | (#28495013)

Fancy that. After all these years of hearing about surface features that were "obviously" formed by water, we find that dry old sand can do the same thing, pushed along by the winds over the millenia.

Poor Mars, our little friend was never wet. It was always a desert, and there is no life.

Earth quakes (1)

flyingfsck (986395) | more than 5 years ago | (#28495157)

This is well known. Earth quakes can cause sandy soil to flow and cause buildings to sink.

The fluidic properties of particulates are used to process ores, grains, tobacco dust and flour for example.

Frank Herbert talked about this back in 1969 (0)

Anonymous Coward | more than 5 years ago | (#28495325)

FH: Yes. It was a long time ago. Sand dunes are like waves in a large body of water; they just are slower. And the people treating them as fluid learn to control them.

WM: Fluid mechanics, in other words.

FH: Thatâ(TM)s it. Fluid mechanics, with sand. And the whole idea fascinated me, so I started researching sand dunes and of course from sand dunes itâ(TM)s a logical idea to go into a desert. The way I accumulated data is I start building file folders and before long I saw that I had far to much for an article and far too much for a story, for a short story. So, I didnâ(TM)t know really what I had but I had an enormous amount of data and avenues shooting off at all angles to gather more. And I was following them ⦠I canâ(TM)t read the dictionary, you know; I canâ(TM)t go look up a wordâ¦

http://www.sinanvural.com/seksek/inien/tvd/tvd2.htm

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