For Marta, who always asks why it rains.
What are we going to work on together?
- Let's discover how the sun turns water into vapor.
- We'll learn how vapor cools and forms clouds.
- Let's follow the rain through streams and rivers to the sea.
Marta reached the shore after a rainy morning. Puddles between the rocks reflected the sky. A wave reached her boots and slipped back, leaving a drop on a warm stone. Marta crouched down to look at it.
—Where did you come from? Well, the sea. I know that. But where will you go now?
The sun warmed the stone. Marta held her hand near the drop and felt the heat. She decided to stay a while and see what happened.
Little by little, the drop disappeared from the stone. Marta looked for it in the cracks and under a shell, but there was no water there. She looked at the stone again: it was still warm, and now it was dry.
—You didn't roll away... You evaporated, didn't you?
The sun's heat had turned the liquid water into water vapor, an invisible gas that rises through the air. Marta looked up. She couldn't see the drop, but she could imagine it traveling upward.
As Marta walked along the seaside path, a cloud appeared over the sea. High above, the air was colder. The vapor that had risen cooled down and turned back into tiny drops of water. This change is called condensation; lots of tiny drops together form clouds.
Marta watched the cloud drift slowly along.
—So first you disappear from the stone, and then you meet up with more drops. What a plan!
A breeze pushed the cloud toward land, and Marta continued on her way.
When she reached a bridge, Marta felt a drop land on her hand. Then another fell on the path. So many tiny drops had gathered in the cloud that some were falling as rain. Marta listened to the PLOP of the drops hitting the ground.
—You're back! Though now I don't know which one of you was you.
She smiled and looked under the bridge. The stream caught the rain and ran between the stones. Marta stayed to see where all that water would go.
The stream flowed downhill. Marta walked beside it until she saw it join a wider river. Rainwater that didn't stay in the ground followed that path. Among the fallen leaves, a wrapper was about to reach the current. Marta picked it up and kept it to put in a bin.
—Better for the river to travel without litter.
The river continued toward the sea, and Marta decided to head back too.
Back at the shore, Marta saw where the river met the sea. She sat listening to the waves and thought back over the drop's journey.
—What made it rise? The sun's heat. Where did it join the other drops? In the cloud. How did it return to the ground? As rain.
One question remained: how did it get back to the sea? Marta followed the river with her eyes to where it mingled with the waves. Then a little splash wet her hand.
What have we learned?
- Marta discovered that the sun's warmth turns water into rising vapor.
- Marta learned that vapor cools into tiny drops that gather in clouds.
- Marta discovered that rain can flow through streams and rivers back to the sea.
Questions to think about together
- How do you think Marta felt when she discovered the drop's invisible journey?
- What would you do if you saw litter about to fall into a stream?
- How could rain that falls near you reach the sea?
