Book 6, Question 18
Why Does Wet Sand Hold a Castle?
A little bit of water acts like glue between sand grains. Too dry, and the walls crumble. Too soupy, and they slump. Deep holes can collapse, so keep them small.
From the book
Page from A Million Whys Book 6
More fun facts
- Sand gives a sandcastle its shape, but water between the grains holds it together with suction.
- A sandcastle also needs some air between the grains. With too much water, the grains get pushed apart.
- When sand gets wet, the tiny spaces between grains fill up with water.
- Engineers define sand grains as particles from about 0.003 to 0.187 inches across.
- Scientists who study sediments even talk about the perfect sand-to-water mix for building castles.
Sources: Scientific American, OSU, Scientific American
Questions kids ask
Why does a sandcastle fall apart when it gets too wet?
Too much water pushes the sand grains apart, so the suction that held them together is lost.