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So I came across this interesting video in which shade-balls were dropped into a swimming pool and people tried to swim around.

Towards the end of the video, a smaller part of the pool is filled with a thick layer of shade-balls and the poster of the video lays on top of the layer, eventually sinking and claiming that the shade-balls where behaving as quicksands.

I was struck by this remark and I was wondering if perhaps shade-balls are in some way analogous to quicksand.

Shade-balls are rigid plastic balls of diameter around 10-13 cm (I'd say), filled with water and air (more or less half water and half air). They therefore are less dense than both water and the human body. Moreover due to their shape there always are many gaps (around 9% of the total volume covered, according to the video).

While I would expect quicksands to be denser than human body, I think that the low density (numerous gaps) of the "shade-balls fluid" and relatively strong friction between shade-balls may cause them to act similarly to quicksands or to some other non-newtonian fluid. Here I am thinking more to a meters-thick layer of shade-balls, maybe with some water underneath (which is probably necessary to help making more fluid the balls, right?)

AoZora
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1 Answers1

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Overall the analogy does not hold up.

An essential aspect of quicksand is that its density is higher than that of the human body. As a consequence, when you are in quicksand you have positive buoyancy, you will sink down at most to half your body volume.

The danger of quicksand is not that you can become submerged in it; you cannot. The danger is that if you do everything wrong extracting yourself becomes impossible. Then if tide or flood water comes in you drown. In that sense the comparison fails completely.

Still, there is a specific aspect for which the two case are analogous.
Your foot will not instantly sink into quicksand because of friction between the sand particles. If you stimulate the inflow of water then friction between the sand particles drops, and your feet can start sinking.

So the parallel is that in both cases there is barely enough friction between the particles to behave like a solid. A little agitation and the behavior becomes more liquid-like.

Cleonis
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