Science Of Sand Castles
It's taken ten thousand years of civilisation but finally someone has taken the time to study sand castles. Wet sand, it seems, has some curious properties. B. James McCallum and Stuart M. Smith were more than happy to get on the case.
If you take children to the beach, most likely they will get bored with swimming and start seeking alternative means of amusement. Luckily, the beach itself offers its own brand of fun. As every five-year-old knows, mix water and sand together and you get a malleable building material perfect for making all types of structures - most commonly, the sand castle.
If you take scientists to the beach, most likely they will get bored with swimming and start seeking alternative means of amusement. Apparently they start wondering “Why can any five-year-old haphazardly mix sand and water get a malleable building material suitable for building a sand castle?” Thanks to an international team of researchers from Germany, Australia, and Switzerland, hundreds of vacationing scientists will now have to amuse themselves in other ways.
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As it turns out, the stiffness of the wet sand remains relatively constant with a water content of anywhere from 1 to 10 percent. At higher percentages, sand and water flow, well, like water. Below that critical level, however, a curious event occurs. As sand is not of uniform size or shape, it does not pack together tightly on a microscopic level. If there is not enough water to fill in all the space between sand crystals, the water effectively seeks shelter. Due to surface tension, it insinuates itself between sand granules in places where the irregular crystals’ surfaces touch each other, seeking to surround itself with as much surface as possible. It then acts like glue attaching one granule to another, building small arches, bridges, and flying buttresses of sand.
What about the rest of the space? The left-over, naked part of a sand granule that’s not touching another granule is a relatively inhospitable place to be for water molecules and those spaces are left filled largely with air. According to the new research, the resulting filigree structure has a very consistent internal pressure and strength, pretty much regardless of the amount of water present, hence the consistency in stiffness over the wide range of water content.
The research doesn’t apply to just sand, it does have practical applications – the findings can be applied to everything from wet grain in a silo to powdered medications, and maybe even to landslides. Oh, and finally scientist and children can co-exist at the beach, each happy in their own way. Get more from James and Stuart or follow our lead:
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Title: GetupGirl; Image: Ariel Camilo
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