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Researchers Discover That Sand Behaves Like Water
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."
Quicksand discovered !!!
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.
Haven't they heard of strobe lights?
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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?
The finer the sand the more it acts like this, that's your "water on mars" right there.
"If any question why we died, Tell them because our fathers lied."
It's probably just due to static electricity.
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)
The government which is strong enough to protect you from everything is strong enough to take everything from you.
Is a camel still the ship of the desert?
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.
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.
The next time a crystalline life form insults me I'll play the kindergarten card and say "I know you are but what am I."
Huh. /Someone/ has been playing too much of that nifty little toy The Falling Sand Game and calling it research.
if the answer isn't violence, neither is your silence / freedom of expression doesn't make it alright
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
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.
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....
Call me when they can run linux on sand.
(Edit: Please note phone is off, due to slashdotting)
I record my sleeptalking
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.
Gotta say, the Vid is very cool - Especially if you're stoned :P
Evacuate and try it again...
Seastead this.
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.
Hasn't this pretty much already been used in a physics engine? The Octave Engine, for instance, can simulate quite a few different small particle system with very similar results.
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.
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.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
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.
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.
http://CryoLANparty.com/ A lan I'm staff on!
...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.
Well, that makes things easier for sandworms.
Freedom would be not to choose between black and white but to abjure such prescribed choices. -Theodor Adorno
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.
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.
Seven puppies were harmed during the making of this post.
Air is being pushed around the outside of the larger masses, causing the grains to coagulate into "drops".
Quicksand discovered !!!
Quicksand is rather a colloidal suspension requiring an underground water source:
http://en.wikipedia.org/wiki/Quicksand
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.
This is my sig.
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.
Excuse me, but please get off my Pennisetum Clandestinum, eh!
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.
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
In other news, today scientists announced that sand is wet. Well duh! What are we paying these guys for? I could have told you that... wait, sand? _Sand_ is wet? WTH?
This Space Intentionally Left Blank
While the physicists are still playing around with this, the engineers have been commercially using these phenomena in their fluidized beds for years. In the field of metallurgy (specifically, heat treating), fluidized beds have been used in place of molten salt baths.
showed this when they used sand to stop a bank robber and his get away car by blowing air under the sand and it fluctuated just like water would have and caused the guy and car to sink, and once the air was stopped the sand solidified again.
That which does not kill me only postpones the inevitable.
I knew some guys who were studying this when I was an undergrad, and it wasn't new then: http://en.wikipedia.org/wiki/Fluidized_bed
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
Do the same effects occur in a vacuum?
Well, you know what they say, camels are the ships of the desert.
Agreed, maybe the sand most physicists tend to grow up with is much grainier or something, but any sand I ever played with as a kid has always behaved like a fluid. Clearly this is more low-level particle interaction stuff, but I'm still a little shocked that no one's done the research before now, if there's anything practical to be gained from studying it in more detail. There does seem to be a lot of research of the obvious these days, for the sake of every student being able to claim authorship of some paper or other, but hopefully there's a sensible reason for the study in this case.
The strobe light effect you mention appears to slow down, stop, or reverse falling droplets, but is merely an illusion. The individual droplets in each frame are actually replaced by successive droplets that are sufficiently similar-looking to give the illusion that you're seeing one individual droplet frozen in space.
With the sand example, the droplets are visibly different in size and shape. You don't want some sleight-of-hand trick with a strobe light, where you turn out the lights and quickly put a different droplet in place. You want to keep individual droplets in frame and follow them as they form and fall. Having the camera fall in unison with the sand seems like a pretty good way to do it.
I'm no expert, but it appears to me from the video that the effect is most likely "started" by gravity. No, not gravity from particle to particle, but from particle to Earth. As the sand particles fall towards Earth, they accelerate, and after an amount of time "groups" begin to drift apart. What causes them to smooth out I'm not sure.
I could be wrong.
You read the article!
seem to act like water: my kids seem to want to spend my money that way :-(
The geotechnical/geological engineers have also been treating soils as fluids for years -- check out any papers by Oldrich Hungr or Stephen Evans on landslides. Neil Balmforth, a geologist/mathematician, has piles of papers on fluid dynamics of small grains (sands or glass beads).
As a physicist working in earth science, yes, it is really nice to finally have some more solid reasons behind treating soft soils as fluids besides "because it works," but I disagree with the summary's claim that the discovery will lead to a whole new approach to soil sciences since it's already been treated as true for ages.
The same group noted that despite the similarities in behavior, the thirst quenching capabilities of sand lag far behind that of water..
If colored smoke were used you would be able to visualize what is going on with the air surrounding the sand. It would be very interesting.
I just re-read TFA twice, and it mentioned nothing of vacuum. I don't have a subscription to Nature magazine to read the original report, nor do I see a link to the report from TFA, yet everybody's saying "Duh, RTFA!" Can you quote where it says it was actually performed in a vacuum? I'm curious why I missed it.
I for one welcome our new found sand droplet forming overlords and I am more then willing to narc on all those sand castle building sons of bitches!
-=[ Who Is John Galt? ]=-
And I suppose those unbound grains of sand formed into the most aerodynamic assemblage of a shape possible on the way down.
Who'd a thunk?
I've known that finely ground particles of solids can behave like water for about 5 years now. My dad owns a bakery, and whenever we clean our mill, we end up with some superfine flour that was caught in a separator mechanism. When we loaded it into a plastic trashcan for the first time, we discovered that if we kick the trashcan, the flour will squirt out in response to the flexing sidewall, similar to what water would do in the same circumstance. Also, the finely ground flour would always form an almost completely flat surface no matter how much we tried to pile it up. I had always assumed that this was not news to the scientific community. Apparently we weren't just screwing around when we played around with the stuff, we were doing college level physics research on fluid dynamics. My thought on the subject has always been that the air around the fine particles of flour was causing the flour particles to behave like a colloidal suspension, instead of a collection of solids. I always thought that it was the air that causing the particles to behave as a fluid, because the air is a fluid. Furthermore, the company who made our mill, skiold, apparently knew about particles behaving like fluids because they use a unique rotary pump to move the flour through the last portion of the mill.
YouTube link for illustration. (The hydrant failure occurs at 1:19 in the video.) Are you SURE that's not water?
Flowing sand has been considered as a model of hydrodynamics for quite some time. They were using it in studies of turbulence when I was at the Santa Fe Institute 10 years ago. One of the effects of turbulence is the formation of vorticies that persist for much longer than one would expect from the physical characteristics of the sand. The effect was noted and named "self-organizing criticality" 20 years ago http://www.iop.org/EJ/abstract/1402-4896/1990/T33/001 . The result appears as though surface tension were involved but obviously that phenomenon doesn't apply.
I have to admit that dropping the camera to get their pictures is a neat hack.
"I may be synthetic, but I'm not stupid." -- Bishop 341-B
everything else is kinda moot.
1) How uniform are the sizes of each grain?
2) Static charges?
3) Aerodynamics? (see 1)
It may appear to behave like water, no chance I am going to wash my knob with it though.
I'm guessing none of them read it either, and just took the first poster's word for it.
Gravity is so weak that it is all but irrelevant at small scales. They have an interesting peer-reviewed publication in Nature, why do you doubt their explaination?
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
Shh! Don't tell the Somali pirates.
"Old bag" has more than one meaning.
Are they alredy discovered how pronounces letter "Z" ?
Are they discovered already how pronounces letter "Z" ?
When I was in HS I remember visiting the WVU Chemical Engineering Lab and they had this cauldron if you will of sand that when they pumped air into it the sand liquefied in essence and felt/moved like water, yet it wasn't wet. I wonder if this is a similar phenomenom.
Everything warmer than ??? K behaves as a fluid, given enough time.
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