Aavi is right — ice and water are not different substances; they are the same substance in two different states. Thirav’s reasoning only looks at how they behave (hard vs. flowing), not what they are made of. Something being hard or soft, or flowing or not, describes its state, not its identity as a substance.

We can find out by testing it directly: put water in the freezer of a refrigerator and check if it turns into ice, and separately, leave ice out at room temperature and check if it turns into water. If the same material keeps converting back and forth between the two forms, they must be the same substance.

On being left at room temperature, the ice cube gradually melts and turns into water. This confirms that ice and water are indeed the same substance — they are simply two different states (forms) of it. These states differ in behaviour: water flows and splashes, while ice does not.

No — utensils have no soil to absorb the water, so soil-absorption cannot explain this case. Something else (evaporation) must be responsible.

Activity to investigate: Place a measured amount of water on a steel plate and watch closely — if a puddle of water were seeping through the metal, a wet patch or drip would appear on the underside of the plate. If nothing appears below even as the water on top disappears, then the water isn’t seeping through — it must be leaving as vapour into the air instead. This is exactly what Activity 8.2 does.

What do you infer? No water appears on the underside of the plate at any point, even though the water on top steadily shrinks and eventually disappears completely.

Is this activity enough to conclude water doesn’t seep through a steel plate? Yes, reasonably — steel is a solid, non-porous metal with no visible pores for water to pass through, and repeated observation shows no trace of water on the other side, which is good evidence (though a magnifying check or a longer trial could make the conclusion even more certain).

If water hasn’t seeped through, where has it gone? It has converted into its gaseous state, called water vapour — another state of water, just like ice and liquid water.

The sanitiser (mostly alcohol-based) evaporates very quickly — it converts into vapour and escapes into the air, which is also why our hands feel cool right after applying it.

• Maybe some ice came out of the tumbler and melted on the outside.
• Maybe water has seeped out through the walls of the glass.
• Maybe moisture already present in the surrounding air is collecting on the cold surface of the tumbler.
• Maybe the glass itself is “sweating” due to the difference in temperature between inside and outside.

The chain of reasoning in the textbook is a good scientific approach: if water were seeping out, the level of water inside the tumbler should visibly go down. Since the level does not appear to decrease, seeping seems unlikely — but a small decrease might be too small to notice in a short, wide tumbler. Using a tall, narrow bottle instead makes even a slight drop in water level much easier to spot, giving a more reliable test. This step-by-step questioning (propose a reason → test it → refine it) is exactly how a scientific investigation should proceed.

Prediction: The mass will increase, because extra water keeps condensing onto the outside of the cold tumbler from the surrounding air.

Explanation: Water vapour present in the air comes in contact with the cold outer surface of the tumbler and condenses into water droplets. This added water increases the total mass measured on the balance — confirming that condensation, not seepage, is adding this water.

Can we conclude that water is not seeping through the glass, or that all this water is only from condensation? Not conclusively from Activity 8.4 alone — the mass increase shows something is adding water from outside, but doesn’t rule out seepage on its own.

Modification: Mark the water level on the tumbler with a permanent marker or tape. On repeating, the water level inside does not go down, while extra water still collects outside. This proves the tumbler is not leaking, and that the extra water outside comes purely from condensation of atmospheric water vapour.

Ice (solid) keeps its shape regardless of the container. Water (liquid) flows, takes the shape of its container, and can spread — but its volume stays constant. Water vapour (gas) has no fixed shape and spreads to fill all the space available to it.

Reasoning: Solid → Liquid happens by melting (given); the reverse, Liquid → Solid, happens by freezing. Liquid → Gas happens by evaporation; the reverse, Gas → Liquid, happens by condensation.

Evaporation is much faster on a hot day than on a cold day. Higher temperature gives water molecules more energy, so more of them escape into the air as vapour in the same amount of time.

Conclusion: A larger exposed surface area makes water evaporate faster, because more water molecules at the surface are in direct contact with the air and can escape at once.

What if milk were used instead of water? Milk would also evaporate, but more slowly and leave behind a residue, since milk is not pure water — it contains dissolved/suspended fat, sugar and proteins that do not evaporate along with the water.

Condition kept the same: exposed area of water, amount of water, location.
Condition changed: temperature — one sample kept in a warm spot, another in a cool/shaded spot.

This shows that higher temperature increases the rate of evaporation.

• Water evaporates faster in sunlight than in shade, because sunlight provides more heat energy.
• Clothes dry faster on a hot, sunny day for the same reason.
• Clothes also dry faster on a windy day — moving air carries away the water vapour near the surface, allowing more water to evaporate continuously.

So the main conditions that speed up evaporation are: larger exposed surface area, higher temperature, and greater air movement (wind). Lower humidity also helps, while high humidity slows evaporation down.

Since high humidity (lots of water vapour already in the air) slows evaporation, you can speed up drying by:

• Using a fan or blower to increase air movement around the clothes
• Hanging clothes in a well-ventilated area, or spreading them out to increase exposed surface area
• Drying them indoors near gentle heat (like a heater or clothes dryer)

All of these either raise the effective temperature, increase air movement, or increase surface area — the same conditions that speed up evaporation.

The wet sand packed between the two pots keeps evaporating continuously. Since evaporation draws heat from its surroundings, it pulls heat out from the inner pot, keeping the space (and the vegetables/fruits) inside noticeably cooler than the outside temperature — the same cooling principle as the earthen matka.

How long can food stay fresh inside? Typically for several days to about a week, depending on the outside temperature and humidity, how regularly the sand is kept moist, and the type of produce stored.

What else could replace sand? Any material that holds moisture and stays porous, such as fine gravel, coconut coir/husk, or a soaked jute/cloth layer, since these can also hold water for continuous evaporation.

Just as a gas balloon filled with a lighter gas (like helium) rises in air, water vapour is lighter than air, which causes moist air to rise upward into the atmosphere.

I wonder, oh! I wonder so,
Which path does water choose to go?
I wonder, oh! I wonder so,
When does it snow?
I wonder, oh! I got a wonder call,
How does rain fall?
Up as vapour, into a cloud so grey,
Then down as raindrops, finding its way.
I wonder, ponder and dream each day,
As water’s journey takes its way.

(Any creative completion that reflects evaporation, cloud formation and rainfall correctly is a good answer — this is an open, imaginative task.)

Without the burnt paper, little or no haze forms above the water. After adding the burnt newspaper piece, a visible haziness (like a mini cloud) appears above the water as the bottle is squeezed and released.

Why: The burnt newspaper releases extremely tiny, invisible dust/ash particles into the air inside the bottle. Water vapour needs something to condense around — these dust particles act as tiny “seeds,” letting water droplets form around them and become visible as haze. This is the same process by which real clouds form around dust particles high in the atmosphere.

• Upward arrows from the ocean/lake surface → labelled Evaporation (liquid water turning into vapour and rising)
• Grey clouds forming in the sky → labelled Condensation, forming visible Clouds
• Downward arrows/droplets falling from clouds → labelled Rain (over lower land and water) and Snow (over the cold mountain peak)
• Water flowing across land back to the sea → labelled River, feeding into a Lake and finally the Ocean
• Water sinking into the soil → labelled Groundwater

Together, this continuous movement — evaporation from oceans/land, condensation into clouds, precipitation as rain/snow, and flow back through rivers and groundwater into the ocean — is called the water cycle.

Condensation is defined exactly as the change from water vapour (gas) back into liquid water — for example, water droplets forming on a cold glass surface.

(i) Colouring with: (b) water colours and (c) acrylic colours — both use water as a medium; the painting “dries” as this water evaporates, leaving the pigment behind on the paper. (Crayons and pencil colours are solid and involve no evaporation.)

(ii) Writing on paper with: (b) an ink pen — fountain-pen ink is a liquid, and the writing dries on the page mainly because the liquid part of the ink evaporates. (A pencil leaves solid graphite with nothing to evaporate; a ball-point pen uses a thicker paste that dries mostly by soaking into the paper rather than by evaporation.)

Natural grass contains moisture, which keeps evaporating continuously from its blades (along with water vapour released by the living plant). This ongoing evaporation absorbs heat from the surrounding air, cooling the space around it.

Plastic grass has no water content and cannot evaporate anything, so it provides no cooling effect — in fact, being a synthetic material, it may absorb and re-radiate more heat from sunlight, making the space around it feel warmer.

Perfume/cologne, spirit or rubbing alcohol, nail-polish remover (acetone), petrol, kerosene, and phenyl (floor cleaner) — all of these evaporate readily, often faster than water, which is why we can smell them easily.

A fan does not actually add or remove heat by itself — it simply moves air. When air moves faster across a wet surface (like clothes or our sweaty skin), it constantly carries away the water vapour that builds up just above that surface. This keeps the air right next to the wet surface relatively dry, allowing more water molecules to keep evaporating instead of the air becoming saturated and evaporation slowing down.

The heat needed for this evaporation comes from the clothes/skin and the surrounding air itself, not from the fan — the fan only speeds up the rate at which that evaporation can happen. That’s also exactly why a fan feels cooling on our skin: it speeds up evaporation of our sweat, which draws heat away from our body.

Sludge contains a large amount of water. Leaving it in heaps for 3–4 days allows much of this water to evaporate, making the sludge lighter, drier, and smaller in volume.

• Reduces transportation cost: Lighter, less bulky sludge needs fewer trips and less fuel to transport.
• Improves safety: Drier sludge is less likely to spill, splash, or leak during handling and transport, reducing the risk of workers coming into direct contact with harmful, disease-causing liquid waste.

Understanding evaporation helps us dry clothes faster (by choosing sunny, windy, or well-ventilated spots), preserve food properly, plan outdoor activities around weather/humidity, and understand everyday phenomena like sweating, cooling drinks, and even how earthen pots keep water cool.

Water occurs naturally in the solid state as:

• Glaciers and polar ice caps
• Icebergs floating in cold seas
• Snow covering mountain peaks and cold regions
• Hailstones that fall during hailstorms
• Frost that forms on cold surfaces on winter mornings

Water is essential for every living being, so it can feel like something we’re automatically entitled to. But only a very small fraction of all the water on Earth is actually fit for drinking and daily use, and it is shared by everyone — other people, animals, plants and future generations too.

This means that before we think of water as “ours to use freely,” we first have a responsibility to use it wisely: avoid wasting it, fix leaking taps, keep water bodies free from pollution, and not take more than we truly need. If everyone treats access to water only as a right without responsibility, it can quickly become scarce or unsafe for others. Respecting this responsibility is what protects everyone’s right to clean water in the long run.

You can cool it down by sprinkling or wiping it with water — as the water evaporates from the hot seat, it draws heat away from the seat’s surface, cooling it (the same evaporative-cooling principle used by the earthen matka). Other helpful steps: park in the shade to prevent it from heating up in the first place, or use a light-coloured seat cover, which reflects sunlight instead of absorbing it.