💧 Water Cycle in a Bag
Tape a bag of water to a sunny window and watch evaporation, condensation, and precipitation in miniature!
🧰 What you need
🔬 Steps
- 1
Add ¼ cup of water to the zip-lock bag. Add a few drops of blue food colouring.
- 2
Seal the bag completely — press out any extra air before sealing.
💡 Make sure the seal is tight — any leak will let water escape and reduce what you see. - 3
Tape the bag to a sunny window so it gets direct sunlight.
- 4
Check the bag every few hours throughout the day — you'll see water droplets on the upper sides, and by evening the droplets may drip back down!
💡 The blue colour helps you see the water better. You'll see clear droplets (evaporated pure water) while the colour stays at the bottom.
🧠 The Science
The Sun's heat causes liquid water at the bottom of the bag to evaporate — turning into invisible water vapour that rises. The top and sides of the bag are cooler than the air inside. When warm, moist air touches the cool bag surface, the water vapour condenses back into liquid droplets — just like a cold glass fogs up on a humid day. When enough droplets collect, they drip back down — just like rain! This miniature water cycle is exactly what happens on Earth: the Sun heats oceans → water evaporates → rises → condenses into clouds → falls as rain.
📚 Related Lessons
- 🌊 Water Around Us — Water covers most of Earth — in oceans, rivers, lakes, rain, and underground wells!
- ☁️ Clouds and Rain — Clouds form when water vapour rises and cools — and when they get heavy, they release rain that grows our food!
- 🔄 Water Cycle — Water evaporates from oceans, rises as vapour, forms clouds through condensation, and falls as rain — endlessly!