Physicists solve 150-year-old mystery of equation governing sandcastle physics


“This came as a big surprise. I expected a complete breakdown of conventional physics.”

JENNIFER OUELLETTE –  12/9/2020, 1:00 PM

Building sandcastles at the beach is a time-honored tradition around the world, elevated into an art form in recent years thanks to hundreds of annual competitions. While the basic underlying physics is well-known, physicists have continued to gain new insights into this fascinating granular material over the last decade or so. The latest breakthrough comes from Nobel Laureate Andre Geim’s laboratory at the University of Manchester in England, where Geim and his colleagues have solved a mathematical puzzle—the “Kelvin equation“—dating back 150 years, according to a new paper just published in Nature.

All you really need to make a sandcastle is sand and water; the water acts as a kind of glue holding the grains of sand together via capillary forces. Studies have shown that the ideal ratio for building a structurally sound sandcastle is one pail of water for every eight pails of sand, although it’s still possible to build a decent structure with varying water content. But if you want to build the kind of elaborate, towering sandcastles that win competitions, you’d be wise to stick with that ideal ratio.

Ars Technica

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