Book 6, Question 19
Why Do Footprints Fill with Water?
Under wet beach sand, there is more water. When you step, your foot squeezes the grains together. That hidden water rushes into the print.
From the book
Page from A Million Whys Book 6
More fun facts
- When you step on soaked sand, the grains shift and make more space between them.
- Water flows into those new spaces, so for a moment your footprint can look dry.
- When you lift your foot, the grains settle closer together again, leaving less room for the water.
- You might expect squeezing wet sand to push water out, like a sponge, but the opposite happens.
- Materials made of many separate tiny grains, like sand, are called granular materials.
- In some forests, water-filled elephant footprints become tiny homes full of life.
Sources: Scientific American, Scientific American
Questions kids ask
Why does wet sand look dry around my foot?
Your weight shifts the grains, making extra space that pulls the water down for a moment.