Water's Disappearing Act
Class 6 Science · Chapter 8: A Journey through States of Water · NCERT Curiosity section 8.1–8.2
Learn
After a morning shower, Sahil sees puddles all over the playground. By afternoon they are gone. Where did the water go? It did not sink into the hard concrete. It turned into an invisible gas, water vapour, and mixed with the air.
Liquid water changing into water vapour is called evaporation. It happens at all temperatures, slowly, from the surface of the water: from puddles, wet clothes, lakes, seas, even from leaves and our skin.
Can we get the water back? Hold a cold steel plate over a pan of hot water: tiny drops form under the plate. The vapour cooled and turned back into liquid. This is condensation. The drops on the outside of a cold glass of water come from vapour in the air, not from inside the glass!
Explore: evaporation or condensation?
- Sort each change.
Remember
- Evaporation: liquid water → water vapour, from the surface, at any temperature.
- Condensation: water vapour → liquid water when it cools.
Quick check
Where does the water from a puddle go on a sunny day?
- Into the air as water vapour
- It is destroyed
- It turns into ice
- Into the clouds as liquid drops directly
Answer
Into the air as water vapour. It evaporates: the liquid becomes invisible water vapour in the air.
Think about it
Rohan says the water drops on the outside of his cold water bottle leaked through the bottle. How could you show him he is wrong?
One answer
Put coloured water (or ice with food colour) inside. The drops outside will still be clear, so they cannot have come from inside. They come from water vapour in the air condensing on the cold surface.
Practice
Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.