Home Geography for Primary Grades · Lesson XV · Unit 4: Water, air and weather
15. How vapor is changed back to water
Goal: Your child knows that cold turns vapor back into water, and explains the "steam" from a kettle, a misty window, breath on a cold day, and drops on a glass of ice water.
You'll need
- A tall glass or pitcher of ice water
- A dry towel
- A cold plate (from the fridge) and a kettle (adult only)
- A window or mirror to breathe on
- A geography notebook (any notebook kept just for these lessons) and a pencil
What's in the book
Heat changes water into vapor, and cold turns vapor back into water. Near a kettle spout the vapor is invisible; a little farther away it turns into a white cloud of tiny drops, "water-dust." The lesson suggests holding a cold plate over boiling water, looking at misty windows and frosty breath, and watching mist gather on a pitcher of ice water. Write what you have learned about vapor.
The lesson, step by step
Cold does the opposite
Read:
Heat, as you have learned, changes water into vapor.
SayCold does the opposite. It turns vapor back into water.
The kettle's secret (adult only)
An adult boils a kettle. From a safe distance, look closely at the spout. Right at the spout there is a clear space where you see nothing; a little farther out there is a white cloud.
SayThe clear part is vapor. The white part is vapor that has cooled and turned back into tiny drops. The book calls it water-dust.
Safety: the adult then holds a cold plate in the steam for a moment (with an oven mitt) and shows your child the drops on it. Your child does not do this part.
Ice water
Fill a dry glass or pitcher with ice water and set it on the table. Wipe the outside dry. Watch for a few minutes.
Ask the book's questions: What gathers on the outside? Where does it come from? Does it come through the glass from the inside? Would the same thing happen with some other cold object?
Prove it
To show the water is not leaking through, add a few drops of food coloring to the ice water. The drops outside stay clear: they came from the air.
Breath and windows
Breathe on a cold window or mirror. A mist appears and fades. On a frosty morning, see your breath outside.
Ask: Why does the window get wet inside on cold days?
Write it
The book says:
Write out what you have learned about vapor.
Your child writes two or three sentences, such as "Heat turns water into vapor. Cold turns vapor back into water."
Afterwards
Hunt for "vapor turning into water" this week: the bathroom mirror after a shower, a cold can of juice, the car windows on a cold morning.
Answers to the book's problems
The white cloud near a kettle is vapor that has been chilled by the cool air and changed back into tiny drops of water (water-dust). Moisture on the inside of windows in cold weather comes from the vapor in the warm room air, which is cooled by the cold glass; when enough drops gather they run down the pane. Our breath has vapor in it, which turns into tiny drops in frosty air. The drops on a pitcher of ice water come from vapor in the air of the room, not through the pitcher; the little drops of mist join into bigger drops that run down. Any cold object would do the same.
Worked out for this site from the scan. If a number in your copy differs, trust the book.