The Loh Down On Science

Sandcastle Summer School

All of you competitive sandcastle builders, listen up!

This is Sandra Tsing Loh with the Loh Down on Science.

Meet Daniel Bonn and his team of physicists at the University of Amsterdam. They wondered-- as many of us secretly do--how much water is optimal for the perfect sandcastle?

To find out, the team poured handfuls of wet beach sand into PVC pipe molds. They then pounded the sand with a “thumper” at least seventy times to compact it. If there was too much water, when they removed the mold, the tower would collapse from its own weight.

So what’s the right amount? Roughly one percent water and ninety nine-percent sand. With that ratio, you can build a medieval turret eight inches wide by eight feet tall! The water holds the sand in place by forming tiny liquid bridges--also known as capillary bridges--between grains.

Let’s hope that also keeps the shells firmly clamped over those mermaid’s chests. As a mother, I’m just sayin’.

The Loh Down on Science is produced by LDOS Media Lab, with 89.3 KPCC Pasadena. And made possible by the generous support of the Gordon and Betty Moore Foundation.


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