Grades K–2 · Earth & Space
How can a puddle disappear without boiling?
A puddle can slowly become smaller even when it never bubbles or boils. Some water at its surface leaves the liquid and becomes an invisible gas called water vapor. This change is evaporation.
In the diagramEvaporation happens at the liquid surfacewater vapor is invisibleNo bulk boiling is requiredThe dots symbolize molecules, not visible drops rising from a puddle.
Water is made of tiny moving molecules. Some at the surface can leave and join the air. Energy for evaporation comes from the water and its surroundings. Sunshine can help supply energy, but evaporation can happen without direct sunshine too.
Moving air can carry water vapor away, and damp air can slow the drying. The water has not stopped existing: some of it is now in the air. Other water may also soak into the ground, so a shrinking puddle can have more than one explanation.
About this explanation
Starting knowledge: Recognize liquid water and know that air can contain invisible water vapor.
Sources
- U.S. Geological Survey — Evaporation and the Water Cycle