A Journey through States of Water: Class 6 Science · Chapter 8
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What you will learn in A Journey through States of Water
- Show with simple tests that ice, water and water vapour are three states of the same substance
- Explain evaporation and condensation using everyday examples such as drying clothes and a sweating glass
- Compare solids, liquids and gases by their shape, flow and spreading
- Describe how heating and cooling change water from one state to another
- Plan a fair test to find how surface area, heat, wind and humidity change the speed of evaporation
- Explain the cooling effect of evaporation in a matka and a pot-in-pot cooler
- Describe how clouds and rain form and trace water around the water cycle
Original companion text aligned to NCERT Science Class 6, Chapter 8, pp. 143–162. Not affiliated with or endorsed by NCERT.
Ice and water: same or different?
One April afternoon, a sudden storm pelts the school ground with hailstones. You pick one up. It is hard and icy, and you can roll it between your fingers. A minute later, your palm holds only a few drops of water. Are ice and water really two different things?
A friend thinks they are different. Ice for drinks comes from a freezer, she says, so maybe the freezer adds something new to the water. How could you check? A scientist does not settle this by arguing. She sets up a simple test and watches closely.
2/4The cube shrinks as it melts, and water collects below it.
A clear cup stands on a table next to a clock. In the first step a single ice cube sits in the dry cup and the clock reads 0 minutes. In the second step, at 10 minutes, the cube is smaller and a thin layer of water covers the bottom of the cup. In the third step, at 30 minutes, the cube is gone and the cup holds only water. In the last step the cup has been in a freezer, shown by a snowflake, and the water has become a block of ice shaped like the cup.
Ice, liquid water and water vapour are three states of one substance. They behave very differently, though. You can pick up an ice cube and turn it over in your fingers. Try that with water, and it runs through your fingers and drips onto the floor. In this chapter we follow water as it travels from one state to another.
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Answer False
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Answer (C) It keeps its own shape
8.1 Investigating Water’s Disappearing Act
After a heavy monsoon shower, the school ground is dotted with puddles. By the last bell, many of them have shrunk and some have vanished. Where did all that water go?
Water vanishes at home too. Plates in the drying rack drip after washing, yet an hour later they are dry. A steel plate is not like soil. Can water soak into steel and hide inside it? Or does it go somewhere else? Let us test the two ideas.
2/3The puddle shrinks as water leaves as invisible vapour.
A steel plate rests on a pink square of tissue paper. At the start a puddle labelled water sits in the middle of the plate. After 1 hour the puddle is about half as wide and dashed arrows labelled invisible vapour rise from it. After 3 hours the plate is dry and a dashed ring shows where the puddle was. A label says the tissue stays dry the whole time.
The water had only one way out: upward, into the air. On its way it became water vapour, which is water in the form of a gas. Water vapour mixes invisibly with the air, so we cannot see it leave.
The change of liquid water into water vapour (वाष्पन). It happens at the surface of the water, even at room temperature.
ExampleA wet school uniform drying on the balcony.
Evaporation does not wait for water to boil. It goes on quietly all the time, even in a cool room. Wet hair dries. Ink on your notebook dries. A rain-washed road turns dry again. Heat speeds it up: drops sprinkled on a hot tawa hiss and vanish in a second or two.
Now picture a kettle on the stove. When the water boils, a white plume puffs out of the spout. Many people call it steam. Look closely, though. Right at the tip of the spout there is a clear gap, and the white plume starts a little further out.
3/4A little further out, the vapour cools into tiny drops that we can see.
A kettle sits on a lit stove. In the first step nothing comes out of the spout. In the second step a dashed ring just outside the spout marks a clear gap labelled clear gap: vapour, where invisible water vapour leaves. In the third step a cloud of small circles labelled mist of tiny drops appears further from the spout. In the last step the mist drifts away and fades, and the label says the drops dry up again.
The clear gap is pure water vapour, and it is invisible. A little further out, the vapour cools and turns into countless tiny drops of liquid water. Those drops are what you see. Soon they evaporate again, and the white plume fades away.
Now back to the puddles. On a mud playground, some water soaks into the soil and some evaporates. On a cement road, the water cannot soak in, so almost all of it evaporates. So for a mud ground the fair answer is: both.
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Answer (D) Wet clothes drying on a line
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Answer False
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Answer (A) tiny drops of liquid water
8.2 Another Mystery
Take a bottle of cold water out of the fridge on a sticky July day. Within minutes its outside is wet. Tiny drops cover it, then join and roll down. The bottle looks as if it is sweating. Where does this water come from?
3/3Tiny drops join into bigger ones that trickle down.
On the left is a glass of ice-cold water with a tape mark at the water level. On the right is a close-up of the glass wall, with cold water on one side and air with moving dots of water vapour on the other. In the first step the glass is dry and the close-up shows vapour in the air. In the second step the outside of the glass is fogged with a fine mist, and tiny drops form on the cold wall in the close-up. In the third step the drops have joined into bigger drops, one runs down, and a small pool forms at the base. The water level stays at the mark in every step.
Your class may come up with many ideas. Maybe water leaks through the glass. Maybe bits of ice slip out and melt. Maybe the drops come from the air. Good scientists test each idea instead of just picking a favourite. Here is how two friends tested theirs.
Tara and Kabir test three ideas
Three guesses
Tara writes down three guesses. The water leaks through the glass. Melted ice creeps over the rim and runs down. Or the drops come from the air around the glass.
You have met these drops in many places. Grass is wet with dew on winter mornings. The lid of a pot of boiling dal has drops on its underside. The bathroom mirror clouds over after a hot bath. Spectacles fog up when you step out of an air-conditioned room.
In each case, water vapour in the air meets something cold. The vapour cools and turns back into liquid drops. This change is called condensation.
The change of water vapour into liquid water (संघनन). It happens when vapour is cooled, for example by touching a cold surface.
ExampleDrops on the outside of a glass of iced water.
Dew forms in the same way. At night, leaves and grass lose heat and become colder than the air around them. Vapour in the air condenses on them. By mid-morning the sun warms the leaves, and the dew evaporates again.
3/4Vapour has condensed into dew drops.
A large leaf and blades of grass stand on the ground. In the first step, a warm evening, the sun is setting. In the second step, a cool night with a moon and stars, dots of water vapour gather near the leaf, labelled leaf cools. In the third step, dew at dawn, round dew drops sit on the leaf and on the tips of the grass as the sun rises. In the last step the sun is high, the drops shrink, and dashed arrows labelled vapour rises show the dew evaporating.
Could condensation also explain the sweating glass? Kabir’s idea was to weigh it. Let us try his test.
3/3More drops: 487.3 g, and the level has not moved.
A glass of ice water, covered by a steel lid, stands on a digital balance, with a tape mark at the water level. At 0 minutes the glass is dry and the display reads 486.0 g. At 15 minutes small drops cover the outside and the display reads 486.7 g. At 30 minutes bigger drops cover the glass, the display reads 487.3 g, a label says plus 1.3 g heavier, and the mark shows the water level is the same.
What does the balance tell us?
Meena did the weighing test. Her balance read 486.0 g at the start and 487.3 g after 30 minutes. The water level inside stayed at the tape mark. (a) How much water collected on the outside? (b) Where did it come from?
Try it yourself first. Then reveal the solution one step at a time.
A container of warm water drawn as moving particles, with a thermometer. Some particles escape from the surface as vapour. You can switch on a cold plate above the container: vapour particles that reach it slow down and gather into liquid drops on its underside. A temperature slider changes how fast the particles move and how many escape.
- Switch the cold plate off and on. Where do the escaping particles end up each time?
- Lower the temperature of the water. Do fewer particles reach the plate?
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Answer (A) water vapour in the air condenses on the cold glass
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- (A) Dew on grass in the morning
- (B) Drops under the lid of a cooking pot
- (D) A fogged-up bathroom mirror
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Answer humidity
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Answer False
8.3 What are the Different States of Water?
So far we have met water as hard ice, as runny water and as invisible vapour. These are its three states: a solid, a liquid and a gas. What makes each state different? Let us find out by handling them.
3/3Own shape, takes shape, fills space.
Three columns show ice, water and water vapour. In the first step the ice cube sits in a round bowl, the water makes a shallow pool in a bowl, and the vapour, drawn as dots, is packed in a small closed box. In the second step the same ice cube sits unchanged in a tall glass, the same water now makes a tall column in a narrow glass, and the vapour dots have spread through a much bigger closed jar. In the last step labels appear under the columns: own shape, takes shape and fills space.
Three states side by side
Solid (ice)
- Has its own shape
- Does not flow
- Takes up a fixed amount of space
Liquid (water)
- Takes the shape of its container
- Flows and spreads on a surface
- Takes up a fixed amount of space
Gas (water vapour)
- Has no shape of its own
- Flows and spreads in every direction
- Fills all the space it can reach
Water is not the only substance that can be a solid, a liquid or a gas. Look around your classroom and sort what you see. The blackboard, your steel water bottle and a cricket ball are solids. Ink, coconut water and honey are liquids.
Gases are harder to spot, because most of them are invisible. The air around you is a mixture of gases, mostly nitrogen and oxygen. The fizz in a bottle of soda is carbon dioxide gas. The fuel that burns in a kitchen gas stove is a gas too.
You can tell that a gas spreads even when you cannot see it. Peel an orange at one end of the classroom. Soon your friends at the far end can smell it. The smell has travelled through the air all the way to them.
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Answer (B) They fill all the space they get
Tap an item on the left, then its match on the right.
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- A steel spoon : solid
- Mustard oil : liquid
- Oxygen : gas
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Answer False
8.4 How can We change the States of Water?
Suppose you want an ice cube to melt fast. You could hold it in a warm palm or set it in the sun. Both give it heat, and heat makes ice melt. Keep heating the water, and it evaporates faster and faster, until it boils away as vapour.
To go the other way, take heat away. Put water in the freezer, and it freezes into ice. Cool water vapour, and it condenses into liquid water.
The change of a solid into a liquid when it is heated (पिघलना).
ExampleIce turning into water in a glass.
The change of a liquid into a solid when it is cooled (जमना).
ExampleWater turning into ice in a freezer tray.
Other substances melt and freeze too. Near the flame of a burning candle, the wax turns into a clear liquid. As it trickles down the side, it cools and hardens again. A spoonful of solid ghee melts the moment it touches a hot roti. And in a cold North Indian winter, coconut oil freezes into a white solid inside its bottle.
4/4Heating moves water up the ladder; cooling moves it down.
Three boxes are stacked: solid ice at the bottom, liquid water in the middle, and gas, water vapour, at the top. In the first step only the boxes are shown. In the second step an orange arrow labelled melting points up from ice to water, and a dashed blue arrow labelled freezing points down. In the third step an orange arrow labelled evaporation points up from water to vapour, and a dashed blue arrow labelled condensation points down. In the last step a long orange arrow on the left says add heat, and a long dashed blue arrow on the right says remove heat.
A closed container of water drawn as particles, with a thermometer and a label that names the state. Below 0 °C the particles sit in a neat pattern and only jiggle: this is ice. Warm it past 0 °C and they slide past one another: liquid water. Near 100 °C they fly apart and fill the container: water vapour. A slider sets the temperature from −20 °C to 120 °C.
- Start at −10 °C and warm the water slowly. At what temperature does the label change to liquid?
- Heat it to 110 °C, then cool it back down. Which changes of state do you see on the way?
Tap an item on the left, then its match on the right.
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- ice → water : melting
- water → ice : freezing
- water → water vapour : evaporation
- water vapour → water : condensation
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Answer (B) freezing
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- (A) melting
- (C) evaporation
8.5 How can Water be Evaporated Faster or Slower?
On washing day, some clothes dry in an hour while others stay damp till evening. On a hot, breezy April day, the clothesline empties fast. In the monsoon, a towel can stay damp for two days. So something controls how fast water evaporates.
Let us test one thing at a time. First question: does it matter how widely the water is spread out?
3/3The plate is dry. The cap is still wet.
Seen from above, a small bottle cap and a large steel plate each hold one teaspoon of water. At the start dashed outlines mark a small area of water in the cap and a large area spread on the plate. After 1 hour the water on the plate has shrunk to a small patch, while the cap still looks full. After 3 hours the plate is marked dry and the cap is marked still wet.
Plan a fair test: does a breeze help?
Arjun wants to know whether a breeze makes water evaporate faster. He has two identical saucers, water, a teaspoon and a table fan. Plan a fair test for him.
Try it yourself first. Then reveal the solution one step at a time.
2/3The katori in the sun loses water faster.
Two identical shallow steel katoris of water sit on the ground, one in sunlight on the left and one in the shade of a tree on the right. At the start both hold the same amount of water. After 30 minutes the katori in the sun is about half empty, with dashed arrows of vapour rising from it, while the katori in the shade has lost only a little. After 1 hour the sunny katori is marked dry and the shady katori still holds most of its water.
Your tests point to four things that speed up evaporation. A larger surface lets more water touch the air. Heat, from the sun or a stove, warms the water. Wind carries away the damp air just above the water. And dry air takes up vapour easily.
The last one explains monsoon laundry. When the air already holds a lot of vapour, we say the humidity is high. Such air takes up new vapour only slowly. So wet clothes stay damp for a long time on rainy days.
An open dish of water drawn as moving particles, with a thermometer and a counter of particles that have escaped into the air. Controls let you change the temperature, turn on a breeze, switch between a small and a large surface, and put a lid on. Warmer particles escape more often, a breeze carries them away, a large surface lets more escape, and a lid stops them leaving.
- Count the escaped particles for 20 seconds with a small surface, then with a large one. Keep everything else the same.
- Turn up the breeze. Does the counter climb faster?
- Put the lid on. What happens to the counter, and why?
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Answer (D) Spread out, in the sun, on a breezy day
- Measure the result
- Keep everything else the same
- Compare and draw a conclusion
- Decide the one thing you will change
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- Decide the one thing you will change
- Keep everything else the same
- Measure the result
- Compare and draw a conclusion
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Answer True
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Answer (C) The time taken to dry
8.6 Cooling Effect
On a scorching afternoon, water from a clay matka tastes wonderfully cool. Water kept in a steel pot in the same room stays warm. Nobody puts ice in the matka. So how does it get cool?
3/3Evaporation carries heat away, so the matka water gets cooler.
A steel pot and a clay matka, both cut open to show the water inside, each hold a thermometer. At the start both thermometers read the same and are labelled warm. In the second step small drops of water appear on the outside of the matka, labelled wet outside, and dashed arrows show vapour leaving its surface; the steel pot stays dry. In the last step orange arrows labelled heat leaves point away from the matka, and its thermometer falls and is labelled cooler, while the steel pot stays warm.
Clay is full of tiny holes called pores. A little water seeps through them and keeps the outside of the matka damp. This water evaporates. To evaporate, water needs heat, and it takes that heat from the pot and the water inside. So the water left inside becomes cooler. This is the cooling effect of evaporation.
When water evaporates from a surface, it takes heat from that surface, so the surface becomes cooler.
ExampleSweat evaporating from your skin cools you down.
You feel the same effect on your own skin. When you sweat, the sweat evaporates and cools your body. A fan helps by carrying away the damp air, so the sweat evaporates faster. Hand sanitiser feels cold because it evaporates very quickly.
People use this trick in many ways. On summer evenings, families sprinkle water on a hot courtyard or roof. As the water evaporates, the floor cools down. Wet khus mats hung in windows cool the breeze that blows through them.
4/4A wet cloth goes on top, and evaporation keeps the inside cool.
A cut-away view of two clay pots. In the first step a big clay pot has a layer of sand at the bottom. In the second step a smaller clay pot stands inside it on the sand. In the third step the gap between the pots is filled with sand dotted with water, labelled wet sand. In the last step a pink wet cloth covers the small pot, tomatoes and a chilli sit inside labelled cool inside, and dashed arrows show water vapour leaving the sand and the cloth.
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Answer (D) Water seeping out through the clay evaporates
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Answer False
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Answer (C) humid and still
8.7 How Do Clouds Give us Rain?
Every day, sunshine lifts huge amounts of water vapour from seas, rivers, lakes, wet fields and leaves. Where does all that vapour go? Warm, damp air drifts upward. And the higher you climb, the colder the air gets. That is why hill towns like Shimla stay cool even in May.
Think of the sky as a giant cold glass. Once rising air has cooled enough, its vapour condenses, just like the drops on your iced tumbler. High up, though, there is no glass to condense on. Instead, the vapour collects on floating specks of dust, smoke or sea salt, far too small to see. Each speck gets coated in a tiny droplet of water. Countless droplets floating together make a cloud. So a cloud is liquid water (or, when it is very cold, tiny bits of ice), not vapour.
Cloud droplets are so tiny and light that they stay afloat. As they drift about, they bump into one another and merge. It takes about a million cloud droplets to build a single raindrop! Once a drop is too heavy for the air to hold up, down it comes as rain. In cold weather or strong storms, water can also fall as snowflakes, or as lumps of ice called hail.
5/5Drops too heavy to float fall as rain.
An arrow on the left shows that higher up is colder. In the first step a bubble of warm, moist air with vapour dots rises from the sea. In the second step the bubble is higher and has turned cool. In the third step a cloud has formed, and a close-up panel labelled inside the cloud shows water droplets forming around dark dust specks. In the fourth step the cloud turns grey and the close-up shows small droplets joining a big drop. In the last step rain falls from the cloud and the close-up shows a heavy drop falling.
The water cycle
Now join all the pieces. Water evaporates from oceans, lakes, rivers, soil and leaves. The vapour rises, cools and condenses into clouds. The clouds send the water back down as rain, hail or snow. On land, it flows along streams and rivers or soaks into the ground, and at last it reaches the sea again. This never-ending round trip is called the water cycle.
5/5Rivers and groundwater carry the water back to the ocean.
A landscape with a snowy mountain on the left, land with a lake and a river in the middle, an ocean on the right, and a layer of groundwater below the land. The first step labels where water is stored: ocean, lake, river and groundwater. The second step adds dashed arrows rising from the ocean and the lake, labelled evaporation. The third step adds three clouds, labelled cloud and condensation. The fourth step adds rain falling from a cloud onto the land beside the lake, and snow falling on the mountain top. The last step adds arrows showing the river flowing down to the lake and the sea, and groundwater flowing towards the ocean.
The endless journey of water between the Earth’s surface and the air, through evaporation, condensation, rain or snow, and flow back to the sea (जल चक्र).
ExampleWater from the Bay of Bengal falling as monsoon rain on the hills of Meghalaya and flowing back to the sea.
Imagine all the water on the Earth poured into a one-litre bottle. About 975 mL of it would be salty seawater. Most of the fresh water left over is frozen in ice or hidden deep underground. The fresh water we can easily reach, in rivers, lakes and wells, would barely fill two teaspoons. As towns grow, more and more people share those two teaspoons, and many places run short every summer.
So every drop counts. Turn off the tap while brushing. Get leaking taps fixed. Use the water from washing vegetables for your plants. Never throw waste into rivers and ponds. You will learn more about caring for water in Chapter 11, Nature’s Treasures.
- Vapour condenses on dust into droplets
- Heavy drops fall as rain
- The air cools high up
- Droplets join into bigger drops
- Warm, moist air rises
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- Warm, moist air rises
- The air cools high up
- Vapour condenses on dust into droplets
- Droplets join into bigger drops
- Heavy drops fall as rain
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Answer False
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Answer (B) Smoke specks give the vapour something to condense on
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Answer water cycle
Words to remember
A Journey through States of Water: key points and summary
- Ice, water and water vapour are three states of the same substance (Ice and water).
- Water left in the open slowly turns into invisible water vapour. This is evaporation, and it happens even without boiling (Section 8.1).
- The white plume you see near a kettle is tiny liquid drops; water vapour itself is invisible (Section 8.1).
- When vapour meets something cold, it turns back into liquid. This is condensation, as on a cold glass or as dew (Section 8.2).
- A sweating glass gets heavier while its water level stays the same, so the drops come from the air (the weighing test).
- Solids keep their shape, liquids take the shape of their container, and gases fill all the space they get (Section 8.3).
- Heating causes melting and evaporation; cooling causes condensation and freezing (Section 8.4).
- Water evaporates faster with a larger surface, more heat, more wind and lower humidity (Section 8.5).
- In a fair test we change one thing, keep the rest the same and measure the result (Section 8.5).
- Evaporation takes heat away, which cools sweaty skin, a matka and a pot-in-pot cooler (Section 8.6).
- Rising air cools, and its vapour condenses on dust into cloud droplets that join and fall as rain, hail or snow (Section 8.7).
- The water cycle moves water between the Earth’s surface and the air again and again, and fresh water must be saved (The water cycle).
Practice questions with answers (NCERT “Exercises”)
Questions 1–10 practise the same skills as the NCERT exercises, in new situations. The rest are quick extra checks.
Which of these is an example of condensation?
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Answer (D) Drops forming on the outside of a cold soft-drink can
Condensation is vapour turning into liquid, as on the cold can. Fading footprints show evaporation, the kulfi shows melting, and the ice tray shows freezing.In each case, pick the job in which evaporation plays a big part.
Decorating a wall:
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Answer (A) painting it with water-based paint
Water-based paint dries as its water evaporates. Tape and nails involve no drying.Working in the kitchen:
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Answer (B) drying papads in the sun
Papads are dried in the sun, so the water in them evaporates. The other jobs involve no drying.
Two rooftops stand side by side in the same colony. One has a small lawn and many potted plants; the other has bare cement tiles. On a May afternoon, the planted roof feels cooler. Explain why.
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AnswerWater evaporating from the leaves and the damp soil takes heat away, so the planted roof stays cooler.
Plants draw water from the soil and give some of it off as water vapour through their leaves. Water also evaporates from the damp soil in the pots and the lawn.
Evaporation takes heat from the surroundings, so the air and surfaces near the plants are cooled. Bare tiles have no water to evaporate. They only soak up the sun’s heat, so they feel much hotter.
Water is not the only liquid that disappears into the air. Name three other liquids you have seen evaporate, and say what told you each one was evaporating.
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AnswerFor example: hand sanitiser, perfume or attar, and nail-polish remover.
- Hand sanitiser vanishes from your palms in seconds and leaves them feeling cool.
- Perfume or attar on a cotton swab gets fainter as it evaporates, and its smell spreads through the room.
- A few drops of nail-polish remover on cotton dry up almost at once.
- Petrol smells strongly at a filling station because some of it evaporates into the air.
Riya says: “A fan blows cool air, and cool air slows down evaporation. So clothes should dry more slowly under a fan.” Yet her clothes dry faster under the fan. Where is her reasoning wrong?
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AnswerThe fan does not make the air colder; it only moves it. Moving air carries away the damp air next to the cloth, so evaporation is faster.
A fan only moves the air in the room. The air stays at room temperature, so Riya’s first step is wrong.
Next to a wet cloth, the air soon fills up with water vapour, and damp air takes up more vapour only slowly. The fan keeps replacing this damp air with drier air, so water keeps evaporating quickly.
We feel cool under a fan because it speeds up the evaporation of our sweat, and that evaporation takes heat from our skin. The air itself is no colder.
After threshing, a farmer spreads the wet paddy in a thin layer on the threshing floor. She leaves it in the sun for two days. Only then is it packed into sacks and taken by tractor to the storehouse. Explain how waiting saves money and makes the grain easier to handle.
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AnswerWater evaporates from the grain, so the sacks are lighter. Each trip carries more grain, so fewer trips and less fuel are needed, and dry grain is easier to lift and store.
Freshly threshed paddy holds a lot of water. Spread in a thin layer, it has a large surface open to the sun and the breeze. So much of this water evaporates in two days.
The same grain now weighs less. The tractor can carry more of it in each trip, so fewer trips are needed and less money is spent on fuel. Lighter, drier sacks are also easier and safer for workers to lift. And dry grain does not stick together or rot in the storehouse.
Keep a “water-disappearing diary” at home for one day. List five activities in which evaporation happens. For each one, say whether evaporation helps or is a nuisance. How does knowing about evaporation help your family?
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A sample diary:
- Clothes drying on the line: helps.
- The floor drying after mopping: helps.
- Water boiling away from a pot of rice: a nuisance if the rice burns.
- Sweat drying on your skin: helps to keep you cool.
- Water in an open bucket going down on a hot day: a nuisance, as water is lost.
Knowing about evaporation helps us plan. We spread clothes out in the sun and wind, keep stored water covered, and use a matka to cool drinking water.
Ice cubes come from a freezer. Name three places or times where nature itself makes solid water.
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AnswerSnow and glaciers on high mountains, the ice sheets near the North and South Poles, and hailstones in some storms.
Snow and glaciers cover the high Himalayas all year round. Thick sheets of ice cover the lands and seas near the North and South Poles. Hailstones sometimes fall during storms. Frost on grass on very cold winter mornings is another example.
Your school is making posters for World Water Day. The Earth is called the blue planet because so much of it is covered with water. Why, then, do we still need to save water? Give two reasons and three things your family can do.
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AnswerMost of the Earth’s water is salty, and fresh water is limited while the number of users keeps growing. Families can turn off taps, fix leaks and reuse water.
Most of the Earth’s water is salty seawater. Only a small share is fresh water in rivers, lakes and underground, and it is not spread evenly. As the number of people grows, more of us must share this small supply, so many places run short in summer. Polluted water is not safe to use, which makes the supply even smaller.
At home we can turn off the tap while brushing, get leaking taps fixed, and reuse water from washing vegetables to water plants. We can also make sure no waste goes into drains and ponds.
A steel slide in the park is too hot to touch on a summer afternoon. Suggest a quick way to cool it down, and explain why it works.
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AnswerSprinkle some water on it, or wipe it with a wet cloth. As the water evaporates, it takes heat from the slide.
Sprinkle a little water on the slide, or wipe it with a wet cloth. The water evaporates quickly from the hot steel, and evaporation takes heat from the surface. After a few minutes the slide is cooler. Wetting it again when it dries cools it further.
Water vapour turning back into liquid water is called .
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Answer condensation
Condensation is the change from vapour to liquid, the opposite of evaporation.An ice cube is put in an open steel pan on a hot stove and left there. Put what you would see in the pan in order, from first to last.
- only water, getting hotter
- ice floating in a little water
- an empty, dry pan
- a solid ice cube
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Answer- a solid ice cube
- ice floating in a little water
- only water, getting hotter
- an empty, dry pan
Heat first melts the ice into water. More heat makes the water evaporate faster and faster, until it boils away as vapour and the pan is left dry.Match each observation with the change that causes it.
Tap an item on the left, then its match on the right.
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Answer- Clothes drying on a line : evaporation
- Dew on grass at dawn : condensation
- Butter softening in the sun : melting
- Water turning to ice in a freezer : freezing
Drying is evaporation, dew is condensation, softening butter is melting, and ice-making is freezing.Spreading out wet clothes makes them dry faster than leaving them in a heap.
Show answer
Answer True
Spreading them out gives the water a larger surface touching the air, so it evaporates faster.In a weighing test, a covered glass of ice water read 352.4 g at the start and 353.2 g after 20 minutes. How many grams of water condensed on the outside?
gShow answer
Answer 0.8 g
of water condensed from the air onto the cold glass.Which pot will keep drinking water coolest on a hot, dry, breezy day?
Show answer
Answer (C) A clay matka kept in a shady, airy spot
Water seeps through the clay and evaporates fastest in dry, moving air, cooling the water inside. Shade stops the sun from warming it.
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| In your NCERT textbook | Practice question here |
|---|---|
| NCERT Exercises Q1 | Practice Q1 |
| NCERT Exercises Q2 | Practice Q2 |
| NCERT Exercises Q3 | Practice Q3 |
| NCERT Exercises Q4 | Practice Q4 |
| NCERT Exercises Q5 | Practice Q5 |
| NCERT Exercises Q6 | Practice Q6 |
| NCERT Exercises Q7 | Practice Q7 |
| NCERT Exercises Q8 | Practice Q8 |
| NCERT Exercises Q9 | Practice Q9 |
| NCERT Exercises Q10 | Practice Q10 |
Quick check: MCQs on A Journey through States of Water
- Ice and water: same or different?2 questions
- 8.1 Investigating Water’s Disappearing Act3 questions
- 8.2 Another Mystery4 questions
- 8.3 What are the Different States of Water?3 questions
- 8.4 How can We change the States of Water?3 questions
- 8.5 How can Water be Evaporated Faster or Slower?4 questions
- 8.6 Cooling Effect3 questions
- The water cycle4 questions
Key terms (English–Hindi)
- condensationसंघननsanghanan
- The change of water vapour into liquid water when it is cooled.First seen in the chapter →
- cooling effectशीतलन प्रभावsheetalan prabhav
- The cooling of a surface when water evaporates from it and takes heat away.First seen in the chapter →
- dewओसos
- Drops of water that form on cool leaves and grass when vapour in the air condenses at night.First seen in the chapter →
- evaporationवाष्पनvashpan
- The change of liquid water into water vapour. It happens at the surface, even at room temperature.First seen in the chapter →
- freezingजमनाjamna
- The change of a liquid into a solid on cooling.First seen in the chapter →
- gasगैसgais
- A state with no shape of its own that spreads out to fill all the space it gets, like water vapour.First seen in the chapter →
- humidityआर्द्रताaardrata
- How much water vapour the air is holding. On humid days, wet things dry slowly.First seen in the chapter →
- liquidद्रवdrav
- A state that flows and takes the shape of its container but keeps the same volume, like water.First seen in the chapter →
- meltingपिघलनाpighalna
- The change of a solid into a liquid on heating.First seen in the chapter →
- solidठोसthos
- A state that keeps its own shape and does not flow, like ice.First seen in the chapter →
- stateअवस्थाavastha
- One of the forms a substance can take: solid, liquid or gas.First seen in the chapter →
- water cycleजल चक्रjal chakra
- The endless movement of water between the Earth’s surface and the air by evaporation, condensation, rain or snow, and flow.First seen in the chapter →
- water vapourजलवाष्पjalvashp
- Water in the gas state. It is invisible and mixes with the air.First seen in the chapter →