Book 13, Question 40
Why Does Wet Sand Look Darker than Dry Sand?
Dry sand scatters light off every grain, so it looks pale. Wet sand has a thin film of water around each grain. More light slips inside, where it gets absorbed, so the sand looks darker!
More fun facts
- A single fiber of a white shirt is actually mostly transparent; the many fibers and air pockets together reflect light and make it look white.
- Water fills the tiny air pockets, which removes many reflecting surfaces and makes the material more transparent.
- Water does not make fabric chemically darker; you see the darker skin or cloth behind it through the wet spot.
- Wear a white shirt over a bright orange one, and a wet spot will look more orange, not more black.
- Hold a wet white shirt in front of a bright light and the wet spot looks brighter, because it lets more light through.
- Water fills the air gaps between grains of sand in the same way, so light has fewer surfaces to bounce off before it is absorbed.
- Physicists explain that light inside a wet surface can bounce back off the water film and get another chance to be absorbed.
Sources: Wtamu, wgtn.ac.nz
Questions kids ask
Does wet sand stay dark when it dries?
No. When the water evaporates, air fills the gaps again and the sand looks pale.
Why does a wet spot on a white shirt look darker?
Water makes the cloth more see through, so you notice the darker things behind it.