Grains of wet sand—in this exhibit or on a beach—become closely packed together. When you press on the sand, the nearby sand grains push one another into a more jumbled arrangement, creating a raised area around your finger. Water flows down through the gaps between the grains, leaving dry sand above. This phenomenon is called the wet sand effect, or dilatancy (die-LATE-un-see), because the sand expands, or dilates, under pressure.
- Science Buddies: Compression of Wet Sand
Instructions for recreating and examining this effect in a classroom
- The International Sand Collectors Society
Become a sand collector.
- Wikipedia: Dilatant
The wet-sand effect works because of the dilatant properties of sand. Read more here.