I’ve had a link open in a tab for several weeks now about a particular category of maritime disasters involving the liquefaction of “solid bulk cargo.” I flagged this as interesting because it’s sort of the opposite problem from something I run into every weekend, as I pour out breakfast cereal for the kids:
At the moment, The Pip (age 7) is demanding a mixture of Kix and Cheerios to eat while he watches cartoons, while SteelyKid (age 10) will sometimes-but-not-always eat Cinnamon Toast Crunch. At around the time I first encountered that story from the Conversation, I noticed a striking difference between these in terms of how easily they flow out of the container. I finally got around to taking a good video of it, so I can finally write up the comparison.
As you can see from the video, all three of the cereals are subject to occasional glitches in the flow, where despite the individual particles being plenty small enough to get through the opening, the flow ceases. This is dramatically worse for the Cinnamon Toast Crunch, which consists of large, flat flakes than for the basically spherical Kix. The Cheerios are about the same overall diameter as the Kix, but flatter, and fall somewhere in the middle– the stoppage is slightly worse than for the Kix, but not nearly as bad as for the Cinnamon Toast Crunch.
What’s going on here is a version of the phenomenon known as “jamming” in the study of granular materials. This happens as groups of individual particles become wedged across the mouth of the opening, forming a sort of arch shape where they’re all pressed against each other and locked in place. There’s a nice video of it from a research group at Duke, which color-tags the particles that will eventually form the arch that jams up the flow:
As you can see from the cereal example, this is a phenomenon that depends strongly on the size and shape of the particles involved, and studying how these transitions occur is a rich and active area of physics research.
The cargo ship problem is the opposite of this: a mix of granular particles and some fluid that is usually pretty well jammed in place by gravity will, under certain conditions, suddenly start to flow very easily, like a low-viscosity liquid. If this happens at the wrong time in the hold of a cargo ship, the whole mass can shift to one side in a way that destabilizes the ship, causing it to roll over and sink. Finding ways to understand exactly when and how these transitions occur is another rich and active area of research.
The thing I find fascinating about these problems is that they’re entirely classical. I’m a guy who’s largely built his career on exploring the weird phenomena that result from quantum physics, but while these sudden transitions between easily-flowing and jammed states are weird, there’s nothing quantum about them. The detailed state of any particular one of these mixtures of particles is something you analyze using concepts that would’ve been familiar to Isaac Newton, 300-odd years ago: it’s just a matter of forces acting between pairs of particles in contact with one another.
What makes these problems so rich and fascinating is the sheer number of these pairs of interacting particles. If you could take a snapshot of a material like a frame from that Duke video, you could perfectly well map out all the forces and determine whether it would jam or flow smoothly (for a short time in the future, anyway). But that’s just not practical, so a higher-level description is needed, treating the behavior in a collective way. When you do that, though, these transitions are enormously complex and difficult to predict, making them seem almost as weird as quantum phenomena.
And, of course, this is an enormously high-stakes subject as well, not just in the context of preventing shipping accidents. I remember talking at dinner once with a colleague who at one point had become interested in the physics of sand piles, and spent a while playing around doing some simple experiments on the flow of granular materials. When he started to look into whether this might be a publishable line of research, though, he found that there was already an enormous literature on this subject, mostly in an engineering context. Because, as he pointed out, there are billion-dollar industries out there with a deep and abiding interest in controlling granular flows: construction materials like concrete mix, powdered pharmaceuticals to make pills and capsules, and even breakfast cereals. Any erratic behavior in the flow of these materials ends up reducing efficiency and that affects the bottom line for these major corporations, who as a result have funded numerous efforts to find the best ways to move this kind of stuff around. (My colleague decided that, in light of that, it wasn’t a good use of resources to pursue that research more seriously, because of the vast amount of catching-up he would’ve needed to do…)
So, anyway, this is another example of the way surprisingly simple physics produces surprising results when applied to collections of too many particles. This happens on scales from the utterly trivial to the enormously significant, but in the end it all comes back to basic principles of physics.
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At the minute, The Pip( age 7) is requiring a mix of Kix and Cheerios to consume while he enjoys animations, while SteelyKid (age 10) will sometimes-but-not-always consume Cinnamon Toast Crunch. At around the time I initially experienced that story from the Discussion, I observed a striking distinction in between these in regards to how quickly they drain of the container. I lastly navigated to taking an excellent video of it, so I can lastly write the contrast.
As you can see from the video, all 3 of the cereals go through periodic problems in the circulation, where in spite of the private particles being plenty little sufficient to survive the opening, the circulation stops. This is significantly even worse for the Cinnamon Toast Crunch, which includes big, flat flakes than for the generally round Kix. The Cheerios have to do with the exact same total size as the Kix, however flatter, and fall someplace in the middle– the interruption is somewhat even worse than for the Kix, however not almost as bad when it comes to the Cinnamon Toast Crunch.
(************ )What’s going on here is a variation of the phenomenon called “jamming” in the research study of granular products. This takes place as groups of private particles end up being wedged throughout the mouth of the opening, forming a sort of arch shape where they’re all pushed versus each other and secured location. There’s a great video of it from a research study group at Duke, which color-tags the particles that will ultimately form the arch that jams up the circulation:
(*************** )(***** )
As you can see from the cereal example, this is a phenomenon that depends highly on the shapes and size of the particles included, and studying how these shifts take place is an abundant and active location of physics research study.