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NCERT Solutions Curiosity Chapter 8 Making a cloud inside a plastic bottle — Activity 8.10: Let us engage in a group activity

Book page 158 Updated on2026-09-05

Q1.
Pour about one cup of water into an empty one litre plastic bottle, close the lid tightly, squeeze and release the bottle continuously for about 2–3 minutes and observe the space above the water in the bottle. What will you observe?
Answer

Almost nothing happens. The space above the water stays clear, or at most a very faint mistiness appears for a fraction of a second when you release the bottle, and it vanishes at once.

What is going on inside:

  • Squeezing raises the pressure of the air inside; releasing it suddenly lowers the pressure, and the air inside cools a little.
  • The air in the bottle certainly contains water vapour from the water below.
  • But there is nothing for the vapour to condense on. The air inside a clean bottle has very few dust particles.
  • So no lasting cloud forms.
Why this first, failed step is the important one: it is the control. Without it, when the cloud appears in the second half of the activity you could not say what caused it — the squeezing, the water, or the smoke. Doing it first without smoke shows clearly that cooling alone is not enough.
Caution: use an empty, discarded bottle with a lid that closes tightly, and do not squeeze so hard that the lid pops off.
Q2.
Repeat the same activity after adding a small burnt piece of newspaper into the water. What will you observe, and why does this happen?
Answer

Now a cloud appears. As the book says — in this case, you will observe some haziness (clouds) above the water in the bottle. Squeeze and the haze clears; release and it comes back, again and again.

Why it happens:

  1. The burnt newspaper releases very small, invisible dust and smoke particles into the bottle.
  2. When the bottle is released, the air inside expands and cools.
  3. The water vapour in the cooled air now has something to gather on, so it condenses around these tiny particles and forms countless minute droplets.
  4. Those floating droplets are exactly what a cloud is — hence the haziness.
  5. Squeezing again warms and compresses the air, the droplets evaporate, and the bottle clears.
Cooling + water vapour + dust particles → tiny droplets → cloud
What the activity demonstrates: it shows the role of dust particles in the formation of clouds. In the sky the same job is done by dust blown off fields and deserts, salt particles from sea spray, smoke and pollen. This is why real air, which is never perfectly clean, forms clouds so readily.
Caution: handle the burning paper carefully, do it under a teacher's supervision, and drop the burnt bit into the water so that it is put out at once.
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