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NCERT Solutions Curiosity Chapter 8 .1 Investigating Water's Disappearing Act — In-text Questions

Book page 1448 Updated on2026-09-05

Q1.
Have you ever noticed water in the puddles disappearing? Where does it go? Discuss with your friends.
Answer

Yes. Puddles that were full of water in the morning are small or completely dry by the evening.

The water leaves the puddle by two routes:

  • It seeps into the ground. Soil, sand and mud have tiny spaces between their grains, and water sinks into them.
  • It evaporates into the air. Water at the surface of the puddle slowly changes into water vapour, which mixes with the air and becomes invisible.
How you can tell that both are happening: a puddle on loose soil vanishes very fast — mostly seeping. A puddle on a cemented floor or a stone slab also dries up, and there the water cannot seep anywhere, so it must have evaporated. In the playground, which has soil, both routes work together.
Tip for the discussion: ask your friends which puddle disappears faster — the one in the sun or the one in the shade of a tree. If seeping were the only reason, the shade should make no difference. It does make a difference, which shows that evaporation is taking place.
Q2.
Where else have you seen water disappearing? Can you think of a possible reason why this happens?
Answer

Water disappears in dozens of everyday situations:

  • Wet clothes on a line dry up.
  • A mopped floor becomes dry in a few minutes.
  • Sweat on our skin dries after we sit in front of a fan.
  • Washed utensils and the wet slab of the kitchen dry by themselves.
  • Water sprinkled on a hot tawa vanishes almost at once.
  • Wet hair dries; a wet handkerchief dries in the pocket.
  • Water in an open glass left overnight is a little less in the morning.
  • Sea water in the shallow pans of a salt farm dries up and leaves salt behind.
The possible reason: in every one of these cases the water is not lost. It changes into water vapour, a gas, and mixes with the air. Because water vapour is invisible, it looks as if the water has disappeared. This process is called evaporation.
Did you know? Nothing in these examples is being heated to 100 °C. Evaporation does not need boiling — it goes on quietly at room temperature, day and night.
Q3.
You might have observed that after washing the utensils, water left on the surface of the utensils, dries up after some time. Does the reason you thought earlier to explain water disappearance apply in this case also?
Answer

Only partly. Of the two reasons given for the puddle, only one can work here.

ReasonPuddle in the playgroundWater on a steel utensil
Seeping into the surfacePossible — soil has spaces between its grainsNot possible — steel is smooth and has no such spaces
Evaporation into the airPossiblePossible — and this is what actually happens

So the "soil absorbed it" explanation does not apply to a steel plate or a steel katori. The water there must be leaving by evaporation.

Why this example is so useful: it is a case in which one of the two possible causes has been ruled out by the nature of the surface itself. Testing an idea in a situation where only one cause can operate is a neat way of separating two mixed-up causes — exactly what a scientist does.
Q4.
Aavi wonders if water has seeped through the surface of the utensils. Thirav thinks that water does not seep through the surface of the utensils. Design an activity to investigate whose idea is correct.
Answer

The activity must be able to show seeping if it happens. So we must be able to look at the other side of the surface while the water is disappearing.

Design:

  1. Take a clean, dry steel plate and wipe its lower surface completely dry.
  2. Put a tablespoon of water in the middle of the upper surface.
  3. Rest the plate on two dry sticks or on the rims of two glasses, so that the lower surface is open to view. Keep a dry sheet of paper underneath.
  4. Every 10 minutes, look at the lower surface and at the paper. Also see how much water is left on top.
  5. Continue until the water on top has completely disappeared.

How to read the result:

  • If drops appear on the lower surface or the paper below gets wet → water is seeping (Aavi's idea).
  • If the lower surface and the paper stay perfectly dry while the water on top vanishes → water is not seeping (Thirav's idea), and it must have gone into the air.
What actually happens: the paper stays dry, so Thirav is right. This is precisely Activity 8.2 in your book.
Tip: Use a fair test — keep a second, identical plate with the same amount of water covered by an upturned bowl. Much less water disappears from the covered one, which shows the water is escaping into the air, not through the steel.
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