"The Science Behind Sandcastles' Structural Integrity"

Sandcastles stay together through a combination of sand, water, and air. Water adheres to the surface of sand grains, forming small bridges that hold the grains together. The strength of these bridges is governed by the surface tension of water. The perfect sandcastle requires one part water for every eight parts dry sand. Angular grains with sharp corners interlock more, increasing stability. Adding a small fraction of clay to the sand helps create more water bridges for sturdier construction. Salt from seawater can help stabilize sandcastles, but they will eventually dry out and become fragile.