WEBVTT

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^- Okay so what I have here is

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^a little tabletop demonstration

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^of this granular sorting phenomena as it applies

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to the Unexploded Ordnance prob.

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So what we have here is a little acrylic box

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and it's half filled with sand

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and the sand is saturated with water.

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You see a little white ball down here at the bottom,

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that's actually Delrin plastic.

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Sitting proud up at the top is a steel ball

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and of course it's sand in the middle here.

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Now when you talk about the density

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of these different materials,

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Delrin is roughly half the density of sand

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and the steel ball is more than twice the density of sand.

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And so what I'm gonna do is I'm gonna take this container

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and I'm gonna start shaking it back and forth

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on the tabletop here.

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What I'm simulating is what waves would be doing

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to the seafloor as they pass overhead and rework the bottom.

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So what you're gonna see immediately is that the steel ball,

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which is more than twice as dense as the sand,

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is immediately gonna bare.

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And you notice the plastic ball hasn't really

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moved anywhere yet.

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And so I haven't been shaking it very hard,

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so I'm gonna shake it a little harder now,

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I'm gonna make the waves bigger

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so the waves are starting to break now.

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And as I shake what you'll see is that the plastic ball

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rises to the top and the steel ball continues to sink.

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And this granular buoyancy phenomena

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is an irreversible process.

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So no matter how hard I keep shaking this,

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that plastic ball will never go back down

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and the steel ball will never come back up to the top.

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Now of course I have a magnet that I used

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to bring the steel ball back up to the top

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to reset the demonstration,

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but this is the granular sorting phenomenon

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that we think explains a large part of the mobility problem.