Level 2 · Science S2.4

Solids, liquids, gases and the water cycle

Ice, water and steam, and the water that goes round and round.

Find out how solids, liquids and gases differ, what melting and drying really are, and how the same water travels from sea to sky and back.

You are ready for this book if

You can say what happens to butter left in the hot sun.

Written and drawn by attnom. Free to read, print and share.

S2.4.1 Chapter 1

Solids, liquids and gases

Why does water change shape, but a stone does not?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

Stones, water and air are all different. See each one in a tall jar and a wide jar.

Three columns, each with a tall jar above a wide jar. In the first column, labelled stone, the same hatched stone sits in both jars and has the same shape. The words under it are keeps its, own shape. In the second column, labelled water, the same amount of dotted water is tall in the tall jar and wide and flat in the wide jar. The words under it are takes the, shape of, its jar. In the third column, labelled air, crossed lines fill the whole of both jars. The words under it are fills the, whole jar. Labels: stone, water, air, keeps its, own shape, takes the, shape of, its jar, fills the, whole jar.stonekeeps itsown shapewatertakes theshape ofits jarairfills thewhole jar
Each one is in a tall jar and in a wide jar. The water is the same amount in both.

We sort materials into three groups.

A solid keeps its own shape. A stone, a spoon and a brick are solids. Put a stone in a cup. It is still the same shape.

A liquid takes the shape of its container. A container holds something, such as a cup or a bottle. Pour water from a tall cup into a wide bowl. The shape changes. The amount does not.

A gas spreads out to fill any container. Air is a gas. Blow up a balloon. The air spreads to fill all of it.

All materials are made of tiny bits, too small to see. In the picture, the bits are dots.

Draw it first

Draw the tiny bits in three boxes

  1. Three boxes of dots. In the box labelled solid, the dots sit in neat rows and all touch. In the box labelled liquid, the dots touch but are jumbled, and they fill only the bottom under a flat top. In the closed box labelled gas, a few dots are far apart, all through the box. Labels: solid, liquid, gas.solid

    1 Draw a box. Fill it with dots in neat rows, all touching. Write solid.

  2. Three boxes of dots. In the box labelled solid, the dots sit in neat rows and all touch. In the box labelled liquid, the dots touch but are jumbled, and they fill only the bottom under a flat top. In the closed box labelled gas, a few dots are far apart, all through the box. Labels: solid, liquid, gas.solidliquid

    2 Draw a second box. Fill the bottom with jumbled dots, all touching. Draw a flat top. Write liquid.

  3. Three boxes of dots. In the box labelled solid, the dots sit in neat rows and all touch. In the box labelled liquid, the dots touch but are jumbled, and they fill only the bottom under a flat top. In the closed box labelled gas, a few dots are far apart, all through the box. Labels: solid, liquid, gas.solidliquidgas

    3 Draw a third box with a lid. Spread a few dots all through it. Write gas.

In a solid, the bits hold their places. So a solid keeps its shape. In a liquid, the bits slide past each other. In a gas, the bits move about freely.

See it three ways

As a picture

Three boxes side by side. In the first box, a small hatched block sits at the bottom, and the rest of the box is empty. In the second box, dots fill the bottom, under a flat top. In the third box, crossed lines fill the whole box. Labels: solid, liquid, gas.solidliquidgas

In words

A solid keeps its own shape, and does not spread. A liquid takes the shape of its container. It rests at the bottom. A gas spreads to fill the whole container.

Try it

Pour water from cup to bowl

You need: a tall cup, a wide bowl, water, a stone, a rubber band or string.

Be safe: Do not drink the water. Wipe up spills.

  1. Half fill the tall cup with water. Put the band at the water level.
  2. Pour the water into the wide bowl. Look at its shape.
  3. Pour the water back into the tall cup. Where does it reach?
  4. Put the stone in the cup, then in the bowl. Does its shape change?

What you will see: In the bowl, the water spreads wide and flat. Back in the cup, it reaches the band again, or nearly. The stone keeps its shape in both.

If you cannot try it, this is what happens.
Three pictures in a row, with arrows between them. First, a tall narrow cup holds water up to a mark on its side. Second, the same water is spread wide and flat in a bowl. Third, the water is back in the tall cup, up to the same mark. Labels: cup, bowl, cup again.cupbowlcup again

A wrong idea many people have

Sand pours, so sand is a liquid.

Why it feels right: Sand and salt flow out of a jar, just as water does.

The test that breaks it: Pour a little sand into your hand. Look at a few grains. Pick up one grain. It keeps its shape. Now pour sand onto a plate. It piles up in a heap. Water never piles up like that.

What is true: Sand is a solid. Each grain keeps its own shape. The grains slide past each other, so a heap pours. Salt is the same.

Sand and water on plates. On the left, labelled sand, many tiny black grains make a heap with a pointed top. The words under it are heaps up. In the middle, a circle labelled close up shows one grain made big, a black square, labelled one grain, with the words keeps its, shape. On the right, labelled water, a dotted puddle lies flat and level on a plate. The words under it are lies flat. Labels: sand, heaps up, close up, one grain, keeps its, shape, water, lies flat.sandheaps upclose upone grainkeeps itsshapewaterlies flat
Sand piles up in a heap. Water lies flat.

Key words

solid
keeps its own shape.
liquid
takes the shape of its container. The amount stays the same.
gas
spreads out to fill any container.
container
a thing that holds something, such as a cup.

Back to your guess

The answer is C: A stone keeps its own shape. Water does not.

A stone keeps its own shape. Water takes the shape of whatever holds it.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Which of these keeps its own shape?

    Tap your answer.

    1. Not this one. Air spreads to fill any container. It is a gas. Try another.

    2. Yes, that is right. A stone is a solid. A solid keeps its shape in a cup or a bowl.

    3. Not this one. Water takes the shape of its container. It is a liquid. Try another.

    See the answer

    A stone

    A stone is a solid. A solid keeps its shape in a cup or a bowl.

    • If you chose A: Air spreads to fill any container. It is a gas.
    • If you chose C: Water takes the shape of its container. It is a liquid.

  2. Mei pours juice from a tall glass into a wide bowl. What stays the same?

    Tap your answer.

    1. Not this one. A liquid takes the shape of its container. The shape changes. Try another.

    2. Not this one. No juice was added or lost. The amount stays the same. Try another.

    3. Yes, that is right. The juice takes a new shape in the bowl. No juice is added or lost, so the amount is the same.

    See the answer

    The amount of juice

    The juice takes a new shape in the bowl. No juice is added or lost, so the amount is the same.

    • If you chose A: A liquid takes the shape of its container. The shape changes.
    • If you chose B: No juice was added or lost. The amount stays the same.

  3. Kofi says sand is a liquid, because it pours. Is he right?

    Tap your answer.

    1. Yes, that is right. Look at one grain. It keeps its shape. The grains slide past each other, so a heap of sand pours.

    2. Not this one. Sand and salt pour, but each grain keeps its shape. They are solids. Try another.

    3. Not this one. Sand does not change. It is a solid when it pours and in a heap. Try another.

    See the answer

    No. Each grain keeps its shape, so sand is a solid.

    Look at one grain. It keeps its shape. The grains slide past each other, so a heap of sand pours.

    • If you chose B: Sand and salt pour, but each grain keeps its shape. They are solids.
    • If you chose C: Sand does not change. It is a solid when it pours and in a heap.

  4. A little gas is let into a closed jar. Where does it go?

    Tap your answer.

    1. Not this one. A liquid rests at the bottom. A gas spreads to fill the whole jar. Try another.

    2. Not this one. A gas does not stay in one lump. It spreads out in every direction. Try another.

    3. Not this one. A gas spreads in every direction, not only up. It fills the whole jar. Try another.

    4. Yes, that is right. A gas spreads out to fill any container. It reaches the top and the bottom.

    See the answer

    It spreads to fill the whole jar.

    A gas spreads out to fill any container. It reaches the top and the bottom.

    • If you chose A: A liquid rests at the bottom. A gas spreads to fill the whole jar.
    • If you chose B: A gas does not stay in one lump. It spreads out in every direction.
    • If you chose C: A gas spreads in every direction, not only up. It fills the whole jar.

  5. Sort these into solids, liquids and gases. Milk. A spoon. The air in a balloon. A brick. Cooking oil.

    See the answer

    Solids: spoon, brick. Liquids: milk, cooking oil. Gas: the air in a balloon.

    A spoon and a brick keep their shape. Milk and oil take the shape of their container. Air spreads to fill the balloon.

  6. Look at the three boxes of dots. Which box shows a liquid?

    Three boxes of dots, labelled A, B and C. In box A, the dots touch but are jumbled, and they fill only the bottom under a flat top. In box B, the dots sit in neat rows and all touch. In the closed box C, a few dots are far apart, all through the box. Labels: A, B, C.ABC
    Tap your answer.

    1. Yes, that is right. In a liquid the dots touch but slide past each other. They fill the bottom, under a flat top.

    2. Not this one. The dots in box B sit in neat rows. They hold their places. That is a solid. Try another.

    3. Not this one. The dots in box C are far apart, all through the box. That is a gas. Try another.

    See the answer

    Box A

    In a liquid the dots touch but slide past each other. They fill the bottom, under a flat top.

    • If you chose B: The dots in box B sit in neat rows. They hold their places. That is a solid.
    • If you chose C: The dots in box C are far apart, all through the box. That is a gas.

  7. Which list has one solid, one liquid and one gas?

    Tap your answer.

    1. Not this one. Sand pours, but each grain keeps its shape. Sand is a solid, so this list has two solids. Try another.

    2. Yes, that is right. Salt is a solid. Oil is a liquid. Air is a gas. Salt pours, but each grain keeps its shape.

    3. Not this one. Honey is thick, but it takes the shape of its jar. It is a liquid. This list has no solid. Try another.

    See the answer

    Salt, oil, air

    Salt is a solid. Oil is a liquid. Air is a gas. Salt pours, but each grain keeps its shape.

    • If you chose A: Sand pours, but each grain keeps its shape. Sand is a solid, so this list has two solids.
    • If you chose C: Honey is thick, but it takes the shape of its jar. It is a liquid. This list has no solid.

Keep it

Copy this into your exercise book.

A solid keeps its shape. A liquid takes the shape of its container, but the amount stays. A gas spreads to fill any container. Sand pours, but each grain is a solid.

Draw: Draw three boxes. Put neat dots in the first. Make a flat pool of dots in the second. Spread a few dots through the third.

S2.4.2 Chapter 2

Air is all around us

Is there anything in an empty cup?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

You cannot see air. But you can feel it when a breeze blows on your face. Air is the gas all around us.

Is an empty cup really empty? Push it into water and see. Turn the cup upside down first.

Draw it first

Draw a cup pushed into water

  1. A bowl with dotted water in it, labelled water. An upside down cup, labelled cup, has a ball of paper stuck inside the top, labelled paper. First the cup is above the water. Then it is pushed down into the water, and an arrow shows the push. The water cannot fill the top of the cup, where the air is, labelled air. The paper stays above the water. Labels: water, paper, cup, air.water

    1 Draw a bowl. Draw the water in it, with dots.

  2. A bowl with dotted water in it, labelled water. An upside down cup, labelled cup, has a ball of paper stuck inside the top, labelled paper. First the cup is above the water. Then it is pushed down into the water, and an arrow shows the push. The water cannot fill the top of the cup, where the air is, labelled air. The paper stays above the water. Labels: water, paper, cup, air.waterpapercup

    2 Draw a cup upside down above the water. Draw a ball of paper in the top of it.

  3. A bowl with dotted water in it, labelled water. An upside down cup, labelled cup, has a ball of paper stuck inside the top, labelled paper. First the cup is above the water. Then it is pushed down into the water, and an arrow shows the push. The water cannot fill the top of the cup, where the air is, labelled air. The paper stays above the water. Labels: water, paper, cup, air.waterpaperaircup

    3 Push the cup straight down. The air stays in the cup. The water cannot reach the paper.

The cup is not empty. It is full of air. Air takes up space. Space is the room that a thing takes up. So the water cannot come in. The paper stays dry.

Air is a material, like water or a stone. It has weight too. A ball full of air is heavier than a flat ball.

A flat, crumpled balloon with a neck and a small knot, labelled flat balloon, lies on the left. An arrow labelled blow points to a round balloon on the right, with a neck and a knot, labelled full of air. Eight small black bits of air are spread through the round balloon. Labels: flat balloon, blow, full of air.flat balloonblowfull of air
Air takes up room. It makes the balloon big.

Moving air is called wind. Moving air pushes things. It pushes a kite, a sail and a leaf. It can also turn a paper windmill.

See it three ways

As a picture

A closed box with a few dots spread all through it. Each dot is a tiny bit of air. A label under the box reads air in a box. Labels: air in a box.air in a box

In words

Air is a gas. A gas spreads out to fill all the space it can. A cup that looks empty is full of air.

Try it

Make a windmill turn

You need: a square of paper, scissors, a pin, a pencil with a rubber on the end.

Be safe: Ask a grown up to help with the pin. Keep it away from your face.

  1. Cut a square of paper. Cut from each corner toward the middle. Stop before the middle.
  2. Fold every other corner to the middle. Pin them to the rubber on the pencil.
  3. Hold the windmill still in still air. Does it turn?
  4. Blow on it, or hold it in the wind. What does the air do to it?

What you will see: In still air, the windmill does not turn. Moving air pushes on the paper, and the windmill turns.

If you cannot try it, this is what happens.
Two paper windmills on sticks. The first, labelled still air, has no arrows near it and does not turn. For the second, labelled moving air, three arrows point toward it, and four small arrows around it show that it turns. Labels: still air, moving air.still airmoving air

A wrong idea many people have

An empty cup has nothing in it.

Why it feels right: You cannot see anything in the cup. It feels light and empty.

The test that breaks it: Push an upside down cup straight down into a bowl of water. Then tip it to one side, under the water. Bubbles rise from the cup. That is the air that was inside.

What is true: An empty cup is full of air. Air is a gas. It takes up space. Water cannot get in until the air goes out.

A bowl of dotted water, labelled water. A cup is tipped under the water, labelled cup. The upper part of the cup is white and holds air, labelled air. Water has come into the lower part, which is dotted. Three round bubbles rise from the high side of its open end toward the top, labelled bubbles. Labels: bubbles, water, cup, air.bubbleswatercupair
Tip the cup under water. The air comes out as bubbles.

Key words

air
the gas all around us.
space
the room that a thing takes up.
wind
air that moves.

Back to your guess

The answer is A: Yes. An empty cup is full of air.

An empty cup is full of air. Air is a gas. It takes up space.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. A cup is pushed upside down into water. A ball of paper inside stays dry. Why?

    Tap your answer.

    1. Not this one. The cup is not empty. It holds air, and air takes up space. Try another.

    2. Not this one. Paper gets wet in water. Here the air keeps the water away from it. Try another.

    3. Yes, that is right. Air is a gas, and it takes up space. The water cannot fill the place where the air is.

    See the answer

    Air inside the cup keeps the water out.

    Air is a gas, and it takes up space. The water cannot fill the place where the air is.

    • If you chose A: The cup is not empty. It holds air, and air takes up space.
    • If you chose B: Paper gets wet in water. Here the air keeps the water away from it.

  2. Which of these is true about air?

    Tap your answer.

    1. Not this one. Air is a material. It takes up space and has weight. Try another.

    2. Yes, that is right. Air spreads to fill any container, so it is a gas. It takes up space too.

    3. Not this one. A liquid takes the shape of its container. It rests at the bottom. Air is a gas. Go to S2.4.1. Try another.

    See the answer

    Air is a gas that takes up space.

    Air spreads to fill any container, so it is a gas. It takes up space too.

    • If you chose A: Air is a material. It takes up space and has weight.
    • If you chose C: A liquid takes the shape of its container. It rests at the bottom. Air is a gas. Go to S2.4.1.

  3. You blow on a paper windmill. What happens?

    Tap your answer.

    1. Yes, that is right. Moving air pushes on the paper, so the windmill turns.

    2. Not this one. Moving air can push. It pushes a sail, a kite and a windmill. Try another.

    3. Not this one. Even a gentle puff of moving air pushes the paper. A strong wind pushes harder. Try another.

    See the answer

    It turns.

    Moving air pushes on the paper, so the windmill turns.

    • If you chose B: Moving air can push. It pushes a sail, a kite and a windmill.
    • If you chose C: Even a gentle puff of moving air pushes the paper. A strong wind pushes harder.

  4. A flat ball and a ball full of air. Which is heavier? Say why.

    See the answer

    The ball full of air. Air has weight.

    Air is a material, so it has weight. The extra air makes the full ball a little heavier.

  5. From an earlier chapter

    Air goes into a closed jar. Where does it go?

    Tap your answer.

    1. Not this one. A liquid rests at the bottom. A gas spreads to fill the whole jar. Go to S2.4.1. Try another.

    2. Not this one. A gas does not stay in one lump. It spreads out in every direction. Go to S2.4.1. Try another.

    3. Not this one. A gas spreads in every direction, not only up. It fills the whole jar. Go to S2.4.1. Try another.

    4. Yes, that is right. Air is a gas. A gas spreads out to fill any container.

    See the answer

    It spreads to fill the whole jar.

    Air is a gas. A gas spreads out to fill any container.

    • If you chose A: A liquid rests at the bottom. A gas spreads to fill the whole jar. Go to S2.4.1.
    • If you chose B: A gas does not stay in one lump. It spreads out in every direction. Go to S2.4.1.
    • If you chose C: A gas spreads in every direction, not only up. It fills the whole jar. Go to S2.4.1.

  6. The wind blows from the left onto a boat with a sail. Which way does the wind push the boat?

    A boat with a mast and one curved sail floats in dotted water, labelled boat and sail. The sail bulges to the right of the mast. Three arrows on the left, labelled wind, point to the right, toward the sail. Labels: wind, sail, boat.windsailboat
    Tap your answer.

    1. Not this one. Moving air pushes things the way it moves. The wind blows to the right. Try another.

    2. Not this one. Air is light, but moving air still pushes. A sail catches the push. Try another.

    3. Yes, that is right. Moving air pushes on the sail. It pushes the boat the way the wind goes.

    See the answer

    To the right, the way the wind blows.

    Moving air pushes on the sail. It pushes the boat the way the wind goes.

    • If you chose A: Moving air pushes things the way it moves. The wind blows to the right.
    • If you chose B: Air is light, but moving air still pushes. A sail catches the push.

  7. Leila wants to show that an empty cup holds air. Which test works?

    Tap your answer.

    1. Not this one. You cannot see air. A good test shows what air does. Try another.

    2. Not this one. Water pushes the air out as it goes in. The air was there first. Try another.

    3. Not this one. Water fills an open cup either way. That does not show the air. Push it in upside down, then tip it. Try another.

    4. Yes, that is right. Bubbles of air rise from the tipped cup. That is the air that was in it.

    See the answer

    Push it upside down into water, then tip it.

    Bubbles of air rise from the tipped cup. That is the air that was in it.

    • If you chose A: You cannot see air. A good test shows what air does.
    • If you chose B: Water pushes the air out as it goes in. The air was there first.
    • If you chose C: Water fills an open cup either way. That does not show the air. Push it in upside down, then tip it.

Keep it

Copy this into your exercise book.

Air is a gas. It is all around you and takes up space. A cup pushed into water keeps water out because it holds air. Moving air pushes things, like a paper windmill.

Draw: Draw a bowl of water. Push an upside down cup into it. Mark the air in the top of the cup.

S2.4.3 Chapter 3

Melting and freezing

Where does my ice go when I leave it in the sun?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

Ice is hard. A puddle of water is not. But ice and water are the same material.

Draw it first

Draw ice melting and freezing

  1. On the left, a box of dots in neat rows, labelled ice. On the right, a box of jumbled dots filling the bottom, labelled water. An arrow points from the ice to the water and is labelled heat. A second arrow points back from the water to the ice and is labelled cool. Labels: ice, water, heat, cool.ice

    1 Draw a box of dots in neat rows. Write ice.

  2. On the left, a box of dots in neat rows, labelled ice. On the right, a box of jumbled dots filling the bottom, labelled water. An arrow points from the ice to the water and is labelled heat. A second arrow points back from the water to the ice and is labelled cool. Labels: ice, water, heat, cool.icewaterheat

    2 Draw an arrow to the right, marked heat. Draw a box of loose dots, marked water.

  3. On the left, a box of dots in neat rows, labelled ice. On the right, a box of jumbled dots filling the bottom, labelled water. An arrow points from the ice to the water and is labelled heat. A second arrow points back from the water to the ice and is labelled cool. Labels: ice, water, heat, cool.icewaterheatcool

    3 Draw an arrow back to the left. Write cool.

Melting is when a solid turns into a liquid. Heat makes things melt. Ice melts into water. Butter and wax melt too.

Freezing is when a liquid turns into a solid. Cooling makes things freeze. Water freezes into ice. Melted wax freezes back into hard wax.

You can undo both changes. Heat ice and it melts. Cool the water and it freezes again.

Melting does not change how much water there is. The water weighs the same as the ice did.

Temperature tells how hot or cold something is. We measure it in degrees Celsius, or °C. Pure water freezes at 0 °C. Ice melts at the same temperature.

A thermometer with a scale from -10 to 10 °C. The liquid stands at 0 °C, marked by a pointer labelled 0 °C. Beside it, a hatched block labelled ice melts at 0 °C, and a dotted block labelled water freezes at 0 °C. Labels: 0 °C, ice melts, at 0 °C, water freezes, -10, -5, 0, 5, 10, °C.-10-50510°C0 °Cice meltsat 0 °Cwater freezesat 0 °C
Ice melts at 0 °C. Water freezes at 0 °C.

Other materials melt at other temperatures. Butter melts on a warm day. Wax needs more heat. A stone does not melt in the sun.

A cup of water with a cube of ice, labelled ice, in it. The ice floats. Most of the cube is under the water, and a small part sticks up above it. The cup is labelled water. Labels: ice, water.icewater
Ice floats. Most of it is under the water.

See it three ways

As a picture

Two boxes side by side. The first box is hatched, to show ice. It is labelled ice, and below it, below 0 °C. The second box is dotted, to show water. It is labelled water, and below it, above 0 °C. Labels: ice, below 0 °C, water, above 0 °C.icebelow 0 °Cwaterabove 0 °C

In words

Heat turns ice into water. Cooling turns water into ice. Both changes can be undone.

In symbols

Pure water freezes at 0 °C. Ice melts at 0 °C. Below 0 °C, water becomes ice. Above 0 °C, ice becomes water.

Try it

Sun or shade: which melts butter faster?

You need: two saucers, butter or a hard cooking fat, a knife, a sunny place, a shady place, a clock or a watch.

Be safe: Do not eat the butter. Do not look at the Sun. A saucer in the sun can get hot.

  1. Cut two pieces of butter the same size. Put one on each saucer.
  2. Put one saucer in the sun. Put the other in the shade.
  3. Look at both every few minutes. Note the time.
  4. Which one gets soft and flat first?

What you will see: The piece in the sun melts first. The piece in the shade melts later. In a cool place it may only get soft.

If you cannot try it, this is what happens.
Two pictures side by side, each with a saucer and butter on it. On the left, the Sun is above. The butter has melted into a flat dotted pool. It is labelled sun. On the right, a tree gives shade above. The butter is still a hatched lump. It is labelled shade. Labels: sun, shade.sunshade

A wrong idea many people have

When a thing melts, it is gone for good.

Why it feels right: A puddle does not look like ice any more.

The test that breaks it: A grown up warms a little candle wax in a tin. Stand the tin in a bowl of hot water. The wax melts. The grown up lifts the tin out. Wait. The wax goes hard again. Never touch hot wax or hot water.

What is true: Melting can be undone. Cool the liquid and it freezes again. It is the same material.

Three tins in a row. The first tin holds a hard lump of wax, labelled hard wax. An arrow labelled heat points to the second tin, which holds flat melted wax, labelled melted. An arrow labelled cool points to the third tin, which holds flat hard wax, labelled hard again. Labels: hard wax, heat, melted, cool, hard again.heatcoolhard waxmeltedhard again
Heat melts wax. Cooling makes it hard again.

Key words

melting
a solid turning into a liquid. Heat makes it happen.
freezing
a liquid turning into a solid. Cooling makes it happen.
temperature
how hot or cold something is.

Back to your guess

The answer is B: It turns into water.

The ice melts. It turns into water. Nothing has gone.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. What turns ice into water?

    Tap your answer.

    1. Yes, that is right. Heat makes a solid melt into a liquid. Ice melts into water.

    2. Not this one. Cooling makes water freeze into ice. Heat makes ice melt. Try another.

    3. Not this one. Shaking does not change ice. It melts when it is heated. Try another.

    See the answer

    Heat

    Heat makes a solid melt into a liquid. Ice melts into water.

    • If you chose B: Cooling makes water freeze into ice. Heat makes ice melt.
    • If you chose C: Shaking does not change ice. It melts when it is heated.

  2. At what temperature does pure water freeze?

    Tap your answer.

    1. Not this one. That is very hot. Water freezes when it is cooled to 0 °C. Try another.

    2. Not this one. At 10 °C, ice melts. Water freezes at 0 °C. Try another.

    3. Not this one. Pure water freezes at 0 °C. It does not need to get colder. Try another.

    4. Yes, that is right. Pure water freezes at 0 °C, and ice melts at 0 °C.

    See the answer

    0 °C

    Pure water freezes at 0 °C, and ice melts at 0 °C.

    • If you chose A: That is very hot. Water freezes when it is cooled to 0 °C.
    • If you chose B: At 10 °C, ice melts. Water freezes at 0 °C.
    • If you chose C: Pure water freezes at 0 °C. It does not need to get colder.

  3. An ice cube is put in a glass of water. What does it do?

    Tap your answer.

    1. Not this one. Ice floats on water. Most of it is under the water, but it does not sink. Try another.

    2. Not this one. Most of an ice cube is under the water. Only a small part sticks up. Try another.

    3. Yes, that is right. Ice floats on water. Most of the cube is under the water. A small part is above it.

    See the answer

    It floats with most of the cube under the water.

    Ice floats on water. Most of the cube is under the water. A small part is above it.

    • If you chose A: Ice floats on water. Most of it is under the water, but it does not sink.
    • If you chose B: Most of an ice cube is under the water. Only a small part sticks up.

  4. Ravi puts butter in the sun and butter in the shade. Which melts first, and why?

    Tap your answer.

    1. Not this one. The shade is cooler. The sun gives the butter more heat, so that piece melts first. Try another.

    2. Not this one. The pieces are the same, but the sun heats one more. That piece melts first. Try another.

    3. Yes, that is right. Heat makes butter melt. The sun heats it more than the shade does. So it melts faster.

    See the answer

    The butter in the sun. The Sun heats it more.

    Heat makes butter melt. The sun heats it more than the shade does. So it melts faster.

    • If you chose A: The shade is cooler. The sun gives the butter more heat, so that piece melts first.
    • If you chose B: The pieces are the same, but the sun heats one more. That piece melts first.

  5. From an earlier chapter

    Ice is a solid and water is a liquid. Which keeps its shape in a cup?

    Tap your answer.

    1. Not this one. Ice and water are the same material. But only the ice keeps its shape. Water takes the shape of the cup. Go to S2.4.1. Try another.

    2. Yes, that is right. Ice is a solid. A solid keeps its own shape.

    3. Not this one. Water takes the shape of its cup. It is a liquid. Go to S2.4.1. Try another.

    See the answer

    Ice

    Ice is a solid. A solid keeps its own shape.

    • If you chose A: Ice and water are the same material. But only the ice keeps its shape. Water takes the shape of the cup. Go to S2.4.1.
    • If you chose C: Water takes the shape of its cup. It is a liquid. Go to S2.4.1.

  6. Two jars of pure water stand outside all night. Each thermometer shows the air by its jar. In which jar will the water freeze?

    Two thermometers with scales from -10 to 10 °C. The thermometer labelled jar A shows the air by jar A and stands at -5 °C. The thermometer labelled jar B shows the air by jar B and stands at 5 °C. Labels: jar A, jar B, -10, -5, 0, 5, 10, °C.-10-50510°Cjar A-10-50510°Cjar B
    Tap your answer.

    1. Yes, that is right. Jar A is below 0 °C. Pure water freezes when it is cooled to 0 °C or below.

    2. Not this one. Jar B is above 0 °C. Water does not freeze there. Try another.

    3. Not this one. Both are cold, but only one is below 0 °C. Water freezes below 0 °C. Try another.

    4. Not this one. Water freezes anywhere that is cooled to 0 °C or below. It does not need a freezer. Try another.

    See the answer

    Jar A

    Jar A is below 0 °C. Pure water freezes when it is cooled to 0 °C or below.

    • If you chose B: Jar B is above 0 °C. Water does not freeze there.
    • If you chose C: Both are cold, but only one is below 0 °C. Water freezes below 0 °C.
    • If you chose D: Water freezes anywhere that is cooled to 0 °C or below. It does not need a freezer.

  7. A grown up warms wax until it melts. Then it cools and goes hard again. What does this show?

    Tap your answer.

    1. Not this one. Cooling the melted wax made it hard again. Melting can be undone. Try another.

    2. Not this one. It is the same wax. It melted, and then it froze again. Try another.

    3. Yes, that is right. Heat melts wax and cooling sets it. The wax is the same material all the way through.

    See the answer

    Melting can be undone by cooling.

    Heat melts wax and cooling sets it. The wax is the same material all the way through.

    • If you chose A: Cooling the melted wax made it hard again. Melting can be undone.
    • If you chose B: It is the same wax. It melted, and then it froze again.

Keep it

Copy this into your exercise book.

Heat makes a solid melt into a liquid. Cooling makes a liquid freeze into a solid. Pure water freezes and ice melts at 0 °C. Ice floats. Butter melts faster in the sun than in the shade.

Draw: Draw a box of ice and a box of water. Draw an arrow marked heat. Draw an arrow back marked cool.

S2.4.4 Chapter 4

Evaporation and drying

Where does the water go when a wet cloth dries?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

Hang a wet cloth in the sun. Later it is dry. Where did the water go?

A wet dotted cloth hangs on a line, labelled wet cloth. Three arrows rise from it, labelled water vapour. An arrow labelled later points to a dry white cloth on the same line, labelled dry cloth. Labels: water vapour, later, wet cloth, dry cloth.water vapourlaterwet clothdry cloth
The wet cloth dries. Its water goes up into the air.

The water did not vanish. It went into the air. It turned into a gas. Water vapour is water as a gas. Evaporation is water turning into water vapour.

You cannot see water vapour. It mixes with the air.

Draw it first

Draw a dish drying out

  1. A dish with dotted water in it, labelled water. Then the water level is lower, labelled less water, and three arrows go up from it into the air. A label above them reads water vapour. Last, the dish is empty, labelled empty dish. The arrows still point up. Labels: water, less water, water vapour, empty dish.water

    1 Draw a dish. Fill it with dotted water.

  2. A dish with dotted water in it, labelled water. Then the water level is lower, labelled less water, and three arrows go up from it into the air. A label above them reads water vapour. Last, the dish is empty, labelled empty dish. The arrows still point up. Labels: water, less water, water vapour, empty dish.water vapourless water

    2 Draw less water. Draw arrows going up. Write water vapour.

  3. A dish with dotted water in it, labelled water. Then the water level is lower, labelled less water, and three arrows go up from it into the air. A label above them reads water vapour. Last, the dish is empty, labelled empty dish. The arrows still point up. Labels: water, less water, water vapour, empty dish.water vapourempty dish

    3 Draw an empty dish. The water is now in the air.

Evaporation goes on all the time, in sun or in shade. It is faster when it is warm. It is faster when wind blows. It is faster when the water is spread out.

Water in a wide dish dries sooner than in a cup. A cold cloth dries too. It just takes longer.

A puddle lies flat on the ground, labelled puddle. The Sun, labelled Sun, shines at the top right. Two arrows on the left, labelled wind, point toward the puddle. Three arrows rise from the puddle, labelled water vapour. Labels: Sun, wind, water vapour, puddle.Sunwindwater vapourpuddle
Sun and wind dry a puddle faster. The water goes up as vapour.

Evaporation is not boiling. Boiling is when water bubbles hard all the way through. Pure water boils at 100 °C at sea level. High up a mountain, it boils at a lower temperature.

Two pictures side by side. On the left, a pot of dotted water with round bubbles all through it, labelled boiling, with the words bubbles, all through. On the right, a shallow dish of water with three arrows rising from the top of the water, labelled evaporating, with the words from the top. Labels: boiling, bubbles, all through, evaporating, from the top.boilingbubblesall throughevaporatingfrom the top
Boiling is hot and bubbly. Evaporation is quiet, at the top.

Boiling water makes steam. Steam is water vapour. You cannot see it. The white cloud over a kettle is not steam. It is tiny drops of water. A later chapter shows how they form.

A kettle on the left, labelled kettle, with a spout. A dashed line leaves the spout. It shows the steam, which you cannot see, labelled steam. Farther along is a dotted cloud labelled tiny drops. Labels: kettle, steam, tiny drops.tiny dropssteamkettle
Steam is the clear part. The white cloud is tiny drops of water.

See it three ways

As a picture

Two boxes with an arrow between them. The first box, labelled water, holds touching dots that fill the bottom. The arrow points to the second box, labelled water vapour. In it, a few dots are far apart all through a closed box. Labels: water, water vapour.waterwater vapour

In words

Water at the top of a puddle slowly turns into water vapour. Water vapour is a gas. It goes into the air.

In symbols

Evaporation: at any temperature. Boiling: pure water at sea level, 100 °C.

Try it

Which place dries a cloth fastest?

You need: three small cloths the same size, a bowl of water, a sunny place, a shady place, a clock or a watch.

Be safe: Do not look at the Sun. Do not drink the water.

  1. Wet all three cloths in the bowl. Wring each one the same.
  2. Spread one cloth flat in the sun. Spread one flat in the shade.
  3. Fold the third cloth into a heap. Put it in the shade.
  4. Touch each cloth every ten minutes. Which one is dry first?

What you will see: The cloth in the sun dries first. The spread cloth in the shade dries next. The folded cloth dries last.

If you cannot try it, this is what happens.
Three black bars show how long each cloth takes to dry. A taller bar means a longer time. The bar labelled sun is the shortest. The bar labelled shade is taller. The bar labelled folded is the tallest. A label above the bars reads time to dry. Labels: time to dry, sun, shade, folded.time to drysunshadefolded

A wrong idea many people have

When a wet cloth dries, the water is gone for good.

Why it feels right: The cloth is dry. You cannot see the water any more.

The test that breaks it: Put a wet cloth in a clear plastic bag. Close it tight. Leave it in the sun for an hour. Look inside the bag. Tiny drops of water cover the inside of the bag. Keep bags away from small children.

What is true: The water went into the air as water vapour. The bag held it in, so some turned back into drops.

Key words

evaporation
water turning into water vapour.
water vapour
water as a gas. You cannot see it.
boiling
water bubbling hard all the way through. It happens only when water is very hot.

Back to your guess

The answer is C: The water goes into the air.

The water goes into the air as a gas. Water does not vanish.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. A wet cloth dries in the sun. Where does the water go?

    Tap your answer.

    1. Not this one. Water does not vanish. It goes into the air as water vapour. Try another.

    2. Yes, that is right. Water evaporates. It turns into a gas, water vapour, and mixes with the air.

    3. Not this one. The cloth is dry, so the water has left it. It is in the air. Try another.

    See the answer

    It goes into the air as water vapour.

    Water evaporates. It turns into a gas, water vapour, and mixes with the air.

    • If you chose A: Water does not vanish. It goes into the air as water vapour.
    • If you chose C: The cloth is dry, so the water has left it. It is in the air.

  2. Which cloth dries fastest?

    Tap your answer.

    1. Yes, that is right. Water evaporates faster when it is warm and spread out.

    2. Not this one. A folded cloth in the shade dries slowly. Warm and spread out is faster. Try another.

    3. Not this one. The bag keeps the vapour in, so the cloth stays wet. The water must reach the open air. Try another.

    See the answer

    Spread out in the warm sun

    Water evaporates faster when it is warm and spread out.

    • If you chose B: A folded cloth in the shade dries slowly. Warm and spread out is faster.
    • If you chose C: The bag keeps the vapour in, so the cloth stays wet. The water must reach the open air.

  3. Is evaporation the same as boiling?

    Tap your answer.

    1. Not this one. Boiling needs a lot of heat. Water also evaporates when it is cool. Try another.

    2. Not this one. Water evaporates in the shade too. It is just slower. Try another.

    3. Yes, that is right. Evaporation happens at any temperature, but slowly when it is cold. Boiling needs water to be very hot.

    See the answer

    No. Water evaporates even when it is not hot.

    Evaporation happens at any temperature, but slowly when it is cold. Boiling needs water to be very hot.

    • If you chose A: Boiling needs a lot of heat. Water also evaporates when it is cool.
    • If you chose B: Water evaporates in the shade too. It is just slower.

  4. What is the white cloud above a kettle?

    Tap your answer.

    1. Not this one. Steam is water vapour, and you cannot see it. The cloud is something else. Try another.

    2. Not this one. There is no fire in the water. The cloud is made of water. Try another.

    3. Not this one. Air is clear, and you cannot see it. The white cloud is made of water. Try another.

    4. Yes, that is right. Steam is clear. The white cloud is tiny drops of water.

    See the answer

    Tiny drops of water

    Steam is clear. The white cloud is tiny drops of water.

    • If you chose A: Steam is water vapour, and you cannot see it. The cloud is something else.
    • If you chose B: There is no fire in the water. The cloud is made of water.
    • If you chose C: Air is clear, and you cannot see it. The white cloud is made of water.

  5. From an earlier chapter

    A puddle of ice sits in the morning sun. Later it is a dry patch. What happened, in order?

    Tap your answer.

    1. Yes, that is right. Heat melts the ice into water. Then the water evaporates into the air.

    2. Not this one. It was already ice. The sun heated it, so it melted first. Go to S2.4.3. Try another.

    3. Not this one. The ice melts first into water. Then the water evaporates. Go to S2.4.3. Try another.

    See the answer

    Melting, then evaporation

    Heat melts the ice into water. Then the water evaporates into the air.

    • If you chose B: It was already ice. The sun heated it, so it melted first. Go to S2.4.3.
    • If you chose C: The ice melts first into water. Then the water evaporates. Go to S2.4.3.

  6. You want wet washing to dry fast. Give two things you can do.

    See the answer

    Spread it out. Hang it in the sun and the wind.

    Water evaporates faster when it is warm, windy and spread out.

  7. Kofi seals a wet cloth in a clear bag. He leaves it in the sun. Drops form inside the bag. Where do they come from?

    Tap your answer.

    1. Not this one. A bag cannot make water. The water was in the wet cloth. Try another.

    2. Yes, that is right. The cloth dried. Its water went into the air in the bag as vapour. Some turned back into drops.

    3. Not this one. The bag is closed plastic. Water does not come through it. The drops came from the cloth. Try another.

    See the answer

    Water left the cloth as vapour and became drops.

    The cloth dried. Its water went into the air in the bag as vapour. Some turned back into drops.

    • If you chose A: A bag cannot make water. The water was in the wet cloth.
    • If you chose C: The bag is closed plastic. Water does not come through it. The drops came from the cloth.

  8. Mei tests where a wet cloth dries fastest. What must be the same for every cloth?

    Tap your answer.

    1. Not this one. The place is the one thing she changes. It is different for each cloth. Try another.

    2. Not this one. The time is what she measures. It will be different. Try another.

    3. Not this one. Then she could not tell what made the difference. A fair test changes one thing. Try another.

    4. Yes, that is right. In a fair test only the place changes. The cloths are the same size and equally wet.

    See the answer

    The size of each cloth and how wet it is

    In a fair test only the place changes. The cloths are the same size and equally wet.

    • If you chose A: The place is the one thing she changes. It is different for each cloth.
    • If you chose B: The time is what she measures. It will be different.
    • If you chose C: Then she could not tell what made the difference. A fair test changes one thing.

Keep it

Copy this into your exercise book.

Water evaporates into the air as a gas called water vapour. It does not vanish. It happens at any temperature. It is faster when warm, windy or spread out. Boiling is different. Steam cannot be seen.

Draw: Draw a dish with a little water. Draw three arrows going up from it. Write water vapour above them.

S2.4.5 Chapter 5

Condensation

Why is the outside of a cold cup wet?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

A cup of cold water stands in a warm room. Soon the outside of the cup is wet. Where does the water come from?

The air holds water vapour. Water vapour is water as a gas. You cannot see it. Evaporation put it there.

Draw it first

Draw why a cold cup gets wet

  1. A cup of cold water, labelled cold water. Small dots in the air round the cup are water vapour, labelled water vapour. Two arrows point from the dots to the cup. Drops of water sit on the outside of the cup, labelled drops.cold water

    1 Draw a cup of cold water. Write cold water.

  2. A cup of cold water, labelled cold water. Small dots in the air round the cup are water vapour, labelled water vapour. Two arrows point from the dots to the cup. Drops of water sit on the outside of the cup, labelled drops.cold waterwater vapour

    2 Draw dots in the air for water vapour. Write water vapour.

  3. A cup of cold water, labelled cold water. Small dots in the air round the cup are water vapour, labelled water vapour. Two arrows point from the dots to the cup. Drops of water sit on the outside of the cup, labelled drops.cold waterwater vapourdrops

    3 Draw arrows from the dots to the cup. Draw drops on the outside. Write drops.

Water vapour in the air touches the cold cup. The vapour cools. It turns back into liquid water.

Condensation is water vapour turning back into liquid. It happens when the vapour touches something cold.

The drops form on the outside of the cup. That is where the air touches the cold cup.

See it three ways

As a picture

Two boxes joined by an arrow. The box on the left holds a few particles spread far apart and is labelled vapour. Above the arrow is the word cools. The box on the right holds particles packed together at the bottom and is labelled liquid.vapourcoolsliquid

In words

Water vapour touches something cold. It cools. It turns into drops of liquid water.

A pot lid does the same. A grown up boils water in a pot. Hot water vapour rises and touches the cooler lid. It turns into drops. The drops run down the lid.

A pot with a lid, labelled pot and lid. Dotted water fills the bottom of the pot, labelled water. Three arrows rise from the water toward the lid, labelled water vapour. Drops hang under the lid, labelled drops. Labels: lid, drops, water vapour, pot, water.liddropswater vapourpotwater
Water vapour touches the cooler lid. It turns into drops.

Grass gets cool at night. Water vapour in the air touches the cool grass. It turns into tiny drops. These drops are dew. Most dew forms on clear, still nights.

Dew is not rain. It does not fall from the sky. It forms right on the grass. It forms on leaves and stones too.

A night scene. A moon, labelled night, is at the top right. Dots in the air, labelled water vapour, drift down toward blades of grass, labelled grass. Small drops, labelled dew, sit on the tips of the grass.water vapournightgrassdew
Dew forms on cool grass at night.

Later the Sun warms the grass. The dew evaporates into the air again.

Try it

Where do the drops come from?

You need: a cup, metal if you have one, the coldest water you can get, with ice if you have it, a little ink or paint to colour the water, a plate, a white cloth, a warm room.

Be safe: Never drink or taste the water in this activity. Ink and paint are not safe.

  1. Fill the cup with the coldest water you can get. Water from a clay pot or a deep well is good.
  2. Stir the ink or paint into the cold water.
  3. Wipe the outside of the cup dry. Stand it on the plate.
  4. Wait ten minutes. Look at the outside of the cup.
  5. Touch a drop with the white cloth. Is it coloured?

What you will see: The outside of the cup gets wet with drops. The drops are clear, not coloured. The coloured water did not come through the cup. The drops came from the air. If no drops form, the water is not cold enough. Try on a damp day, or add ice if you can.

If you cannot try it, this is what happens.
A cup of cold water with ink in it, labelled coloured water. Drops sit on the outside of the cup, labelled clear drops. The drops have no colour.clear dropscoloured water

A wrong idea many people have

The water on a cold cup comes through the cup.

Why it feels right: The cup holds water. So the drops on the outside must have leaked out.

The test that breaks it: If you have a fridge, cool a dry, empty cup in it. Bring it into a warm room. Its outside still gets wet. Or fill a cup with cold coloured water. The drops on the outside are clear. Water that came through the cup would be coloured.

What is true: The drops come from the air. Water vapour touches the cold cup and turns into liquid.

Key words

water vapour
water as a gas. You cannot see it.
condensation
water vapour turning back into liquid on something cold.
dew
tiny drops of water on cool grass and leaves at night.

Back to your guess

The answer is B: The water comes from the air.

The water comes from the air. Water vapour in the air touches the cold cup. It turns into drops.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Where do the drops on a cold cup come from?

    Tap your answer.

    1. Yes, that is right. Water vapour in the air touches the cold cup. It cools and turns into drops.

    2. Not this one. A dry cold cup with nothing inside still gets wet. And coloured water gives clear drops. Try another.

    3. Not this one. Cold does not make water. The water was in the air as vapour. Try another.

    See the answer

    From the air

    Water vapour in the air touches the cold cup. It cools and turns into drops.

    • If you chose B: A dry cold cup with nothing inside still gets wet. And coloured water gives clear drops.
    • If you chose C: Cold does not make water. The water was in the air as vapour.

  2. What is condensation?

    Tap your answer.

    1. Not this one. That is evaporation. Condensation goes the other way. Go to S2.4.4. Try another.

    2. Not this one. That is freezing. In condensation, a gas becomes a liquid. Go to S2.4.3. Try another.

    3. Yes, that is right. Condensation is water vapour turning back into liquid. It happens on something cold.

    See the answer

    Water vapour turning into liquid drops

    Condensation is water vapour turning back into liquid. It happens on something cold.

    • If you chose A: That is evaporation. Condensation goes the other way. Go to S2.4.4.
    • If you chose B: That is freezing. In condensation, a gas becomes a liquid. Go to S2.4.3.

  3. Amina sees dew on the grass in the morning. Where did it come from?

    Tap your answer.

    1. Not this one. Dew is not rain. It forms on the grass from the air. Try another.

    2. Not this one. Air does not turn into water. Only the water vapour in the air turns into drops. Try another.

    3. Not this one. Dew forms from vapour in the air. It does not rise as drops from the ground. Try another.

    4. Yes, that is right. The grass was cool. Vapour touched it and turned into drops of dew.

    See the answer

    Water vapour in the air cooled on the grass.

    The grass was cool. Vapour touched it and turned into drops of dew.

    • If you chose A: Dew is not rain. It forms on the grass from the air.
    • If you chose B: Air does not turn into water. Only the water vapour in the air turns into drops.
    • If you chose C: Dew forms from vapour in the air. It does not rise as drops from the ground.

  4. A grown up boils a pot of water with a lid on. Drops form under the lid. Why?

    Tap your answer.

    1. Not this one. No water is made. The water was in the pot, as vapour. Try another.

    2. Yes, that is right. The vapour cools on the lid and turns back into liquid. This is condensation.

    3. Not this one. The lid is not cold enough to freeze water. The vapour cools into liquid drops. Go to S2.4.3. Try another.

    See the answer

    Hot vapour touches the cooler lid and turns into drops.

    The vapour cools on the lid and turns back into liquid. This is condensation.

    • If you chose A: No water is made. The water was in the pot, as vapour.
    • If you chose C: The lid is not cold enough to freeze water. The vapour cools into liquid drops. Go to S2.4.3.

  5. From an earlier chapter

    Wet washing hangs in the wind. Where does its water go as it dries?

    Tap your answer.

    1. Not this one. Water does not vanish. It evaporates into the air as vapour. Go to S2.4.4. Try another.

    2. Not this one. The washing hangs in the air. Its water evaporates into the air. Go to S2.4.4. Try another.

    3. Yes, that is right. The water evaporates. It turns into water vapour that you cannot see.

    See the answer

    Into the air, as water vapour

    The water evaporates. It turns into water vapour that you cannot see.

    • If you chose A: Water does not vanish. It evaporates into the air as vapour. Go to S2.4.4.
    • If you chose B: The washing hangs in the air. Its water evaporates into the air. Go to S2.4.4.

  6. Draw a cold cup with drops on the outside. Add arrows to show where the water comes from.

    See the answer

    A cup with drops on the outside. Arrows point from the air to the cup.

    The drops come from water vapour in the air. They do not come from inside the cup.

  7. Two glasses stand in the same warm room. One holds cold water. One holds warm water. Which glass gets wet drops on the outside?

    Two glasses side by side. The first holds dotted water with two cubes of ice, labelled cold water. The second holds dotted water with no ice, labelled warm water. Labels: cold water, warm water.cold waterwarm water
    Tap your answer.

    1. Not this one. The outside of that glass is not cold. Vapour turns into drops only on something cold. Try another.

    2. Not this one. Only a cold glass cools the air that touches it. The warm glass stays warm. Try another.

    3. Not this one. The drops do not come from inside the glass. They come from the air, on a cold glass. Try another.

    4. Yes, that is right. Vapour in the room touches the cold glass and turns into drops. The warm glass is not cold enough.

    See the answer

    The glass of cold water

    Vapour in the room touches the cold glass and turns into drops. The warm glass is not cold enough.

    • If you chose A: The outside of that glass is not cold. Vapour turns into drops only on something cold.
    • If you chose B: Only a cold glass cools the air that touches it. The warm glass stays warm.
    • If you chose C: The drops do not come from inside the glass. They come from the air, on a cold glass.

  8. Mei puts a dry, empty cup in a fridge. Later she takes it into a warm room. Drops form on the outside. What does this show?

    Tap your answer.

    1. Yes, that is right. Vapour in the room touched the cold cup and turned into drops. The cup held no water.

    2. Not this one. The cup was empty and dry. It had no water to sweat. Try another.

    3. Not this one. The cup was dry when she took it out. The drops came later, from the air. Try another.

    See the answer

    The water comes from the air in the room.

    Vapour in the room touched the cold cup and turned into drops. The cup held no water.

    • If you chose B: The cup was empty and dry. It had no water to sweat.
    • If you chose C: The cup was dry when she took it out. The drops came later, from the air.

Keep it

Copy this into your exercise book.

Water vapour in the air touches something cold. It cools and turns into drops. This is condensation. It makes drops on a cold cup and dew on grass. The drops come from the air.

Draw: A cold cup. Dots in the air. Arrows to the cup. Drops outside.

S2.4.6 Chapter 6

The water cycle

Where does rain come from, and where does it go?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

Rain falls on a hill. A river carries it to the sea. The sea does not run out. Where does the water go next?

Draw it first

Draw the water cycle

  1. The sea is at the bottom left, a hill at the right, the Sun at the top left and a cloud at the top right. Two arrows go up from the sea, labelled evaporation. An arrow goes to the cloud, labelled condensation. Rain falls from the cloud, labelled rain. An arrow runs down the hill to the sea, labelled flow.

    1 Draw the sea, a hill, the Sun and a cloud. Add the arrows and the rain.

  2. The sea is at the bottom left, a hill at the right, the Sun at the top left and a cloud at the top right. Two arrows go up from the sea, labelled evaporation. An arrow goes to the cloud, labelled condensation. Rain falls from the cloud, labelled rain. An arrow runs down the hill to the sea, labelled flow.evaporation

    2 Write evaporation by the arrows that go up from the sea.

  3. The sea is at the bottom left, a hill at the right, the Sun at the top left and a cloud at the top right. Two arrows go up from the sea, labelled evaporation. An arrow goes to the cloud, labelled condensation. Rain falls from the cloud, labelled rain. An arrow runs down the hill to the sea, labelled flow.evaporationcondensationrain

    3 Write condensation above the cloud. Write rain by the falling rain.

  4. The sea is at the bottom left, a hill at the right, the Sun at the top left and a cloud at the top right. Two arrows go up from the sea, labelled evaporation. An arrow goes to the cloud, labelled condensation. Rain falls from the cloud, labelled rain. An arrow runs down the hill to the sea, labelled flow.evaporationcondensationrainflow

    4 Write flow by the arrow that runs down to the sea.

The Sun warms the sea, the rivers and the wet ground. Warm water turns into water vapour and rises. This is evaporation. The Sun's heat drives it.

High in the sky the air is cold. The vapour cools and turns into tiny drops. This is condensation.

Very many tiny drops make a cloud. A cloud is not water vapour. You cannot see vapour. A cloud is tiny drops of water, or tiny bits of ice.

Below, small black bits far apart, labelled water vapour, with an arrow labelled rises pointing up. Above, a dotted cloud with a bumpy top and a flat base, labelled cloud, with the words tiny drops inside it. Labels: tiny drops, cloud, water vapour, rises.tiny dropscloudwater vapourrises
Vapour is clear. A cloud is tiny drops you can see.

The drops in a cloud join and grow. They get too heavy to float. They fall as rain. Where it is very cold, they fall as snow.

Three pictures in a row, joined by arrows. First, six tiny circles, labelled tiny, drops. Then three bigger circles, labelled drops, join. Last, one big circle with an arrow pointing down from it, labelled rain falls. Labels: tiny, drops, join, rain falls.tinydropsdropsjoinrain falls
Tiny drops join and grow. Then they fall as rain.

Rain soaks into the ground or runs over it. It flows into streams and rivers. The rivers flow down to the sea. Then the Sun warms the sea again.

The whole round trip is the water cycle. It has no start and no end. You can start at any step.

See it three ways

As a picture

Boxes joined by arrows, labelled in order: sea, vapour, cloud, rain, river, sea. Each arrow points to the next box. The last box is the sea again.seavapourcloudrainriversea

In words

Water goes from the sea into the air as vapour. It makes a cloud. It falls as rain. A river flows back to the sea.

The water on Earth is used again and again. A drop in a puddle may once have been in the sea. It may have been in a cloud, or a river. The same water goes round and round.

Try it

Make a small water cycle

You need: a wide bowl, a small cup that is shorter than the bowl, water, clear plastic, such as a bag cut open, string, a small clean stone, a sunny place.

Be safe: Never drink or taste the water from the bowl or the cup.

  1. Pour water into the bowl, about two fingers deep.
  2. Stand the empty cup in the middle. Keep the water out of it.
  3. Cover the bowl with the plastic. Tie it tight with string.
  4. Put the stone on the plastic, over the cup.
  5. Leave the bowl in the sun for a few hours.
  6. Look at the plastic. Look in the cup.

What you will see: Drops form under the plastic. They run down to the stone and drip into the cup. The Sun warmed the water, and it evaporated. The vapour cooled on the plastic and turned back into drops. This is a small water cycle.

If you cannot try it, this is what happens.
A bowl of water, labelled bowl and water, with a small cup, labelled cup, standing in the middle. Plastic, labelled plastic, covers the bowl. A stone, labelled stone, sits on the plastic so that it dips over the cup. The Sun shines from the top right. Arrows go up from the water. Drops cling under the plastic and one drop falls into the cup.plasticstonewatercupbowl

A wrong idea many people have

When a puddle dries up, its water is gone for ever.

Why it feels right: You cannot see where it went. The ground is dry.

The test that breaks it: Use the bowl in the sun. You pour no water into the cup. Hours later, it holds water. That water came from the bowl. It went up as vapour and came down as drops.

What is true: The water goes into the air as vapour. It comes back later as cloud and rain. It goes round the water cycle.

Key words

evaporation
water turning into water vapour.
condensation
water vapour turning back into drops.
cloud
tiny drops of water, or bits of ice, high in the air.
water cycle
the way water goes from the sea to the sky and back.

Back to your guess

The answer is C: The same water goes round and round, again and again.

The Sun lifts water into the air. It cools, falls as rain and flows back. The same water goes round and round.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. What does the Sun's heat do in the water cycle?

    Tap your answer.

    1. Yes, that is right. The Sun warms the sea and wet ground. Water turns into vapour and rises.

    2. Not this one. The Sun does not make water. It moves water into the air. Try another.

    3. Not this one. Rain falls because the drops get heavy. The Sun's heat lifts the water. Try another.

    See the answer

    It makes water evaporate and rise.

    The Sun warms the sea and wet ground. Water turns into vapour and rises.

    • If you chose B: The Sun does not make water. It moves water into the air.
    • If you chose C: Rain falls because the drops get heavy. The Sun's heat lifts the water.

  2. What is a cloud made of?

    Tap your answer.

    1. Not this one. You cannot see water vapour. You can see a cloud. A cloud is drops. Go to S2.4.4. Try another.

    2. Yes, that is right. Vapour cools high up and turns into tiny drops. Many drops make a cloud.

    3. Not this one. Smoke is not water. A cloud is drops of water, or ice. Try another.

    See the answer

    Tiny drops of water, or bits of ice

    Vapour cools high up and turns into tiny drops. Many drops make a cloud.

    • If you chose A: You cannot see water vapour. You can see a cloud. A cloud is drops. Go to S2.4.4.
    • If you chose C: Smoke is not water. A cloud is drops of water, or ice.

  3. Look at the picture. Where does the water cycle start?

    The sea is at the bottom left, a hill at the right, the Sun at the top left and a cloud at the top right. Two arrows go up from the sea, labelled evaporation. An arrow goes to the cloud, labelled condensation. Rain falls from the cloud, labelled rain. An arrow runs down the hill to the sea, labelled flow.evaporationcondensationrainflow
    Tap your answer.

    1. Not this one. The water in the sea came from rivers and rain. The cycle goes round. You can start anywhere. Try another.

    2. Not this one. The cloud was made from vapour that rose from the sea. The cycle has no start. Try another.

    3. Not this one. The rain on the hill came from a cloud. The cloud came from vapour that rose from the sea. Try another.

    4. Yes, that is right. Each step leads to the next. The last leads back to the first. It goes round and round.

    See the answer

    It has no start.

    Each step leads to the next. The last leads back to the first. It goes round and round.

    • If you chose A: The water in the sea came from rivers and rain. The cycle goes round. You can start anywhere.
    • If you chose B: The cloud was made from vapour that rose from the sea. The cycle has no start.
    • If you chose C: The rain on the hill came from a cloud. The cloud came from vapour that rose from the sea.

  4. Rain falls on a hill and runs into a river. Where does the water go next?

    Tap your answer.

    1. Not this one. Water is not lost. It flows to the sea and rises again. Try another.

    2. Not this one. The water must first evaporate. The Sun's heat drives that. Go to S2.4.4. Try another.

    3. Yes, that is right. Rivers flow down to the sea. Then the Sun warms the sea, and the water rises again.

    See the answer

    To the sea

    Rivers flow down to the sea. Then the Sun warms the sea, and the water rises again.

    • If you chose A: Water is not lost. It flows to the sea and rises again.
    • If you chose B: The water must first evaporate. The Sun's heat drives that. Go to S2.4.4.

  5. From an earlier chapter

    Snow lies on a hill. The Sun warms it. What happens to the snow?

    Tap your answer.

    1. Not this one. Warmth does not freeze things. Warmth melts ice and snow. Go to S2.4.3. Try another.

    2. Yes, that is right. Heat melts ice and snow. The water then flows down toward the sea.

    3. Not this one. Snow is ice. Heat melts it, and the water runs downhill. Go to S2.4.3. Try another.

    See the answer

    It melts into liquid water.

    Heat melts ice and snow. The water then flows down toward the sea.

    • If you chose A: Warmth does not freeze things. Warmth melts ice and snow. Go to S2.4.3.
    • If you chose C: Snow is ice. Heat melts it, and the water runs downhill. Go to S2.4.3.

  6. Draw the water cycle. Show evaporation, condensation, rain and flow.

    See the answer

    The sea, the Sun, a cloud and a hill. Arrows go up, to the cloud, down as rain and back.

    Water goes up and makes clouds. It falls as rain and flows back to the sea.

  7. Look at the picture. Which letter shows condensation, where vapour cools into tiny drops?

    The sea is at the bottom left, a hill at the right, the Sun at the top left and a cloud at the top right. Two arrows go up from the sea, labelled C. An arrow goes to the cloud, labelled D. Rain falls from the cloud, labelled A. An arrow runs down the hill to the sea, labelled B. Labels: C, D, A, B.CDAB
    Tap your answer.

    1. Not this one. A is where rain falls from the cloud. Condensation is where the cloud forms. Try another.

    2. Not this one. B is the water flowing down the hill to the sea. Condensation is in the sky. Try another.

    3. Not this one. C is where water rises from the sea as vapour. That is evaporation. Go to S2.4.4. Try another.

    4. Yes, that is right. Vapour cools high in the sky and turns into tiny drops. The drops make the cloud, at D.

    See the answer

    Letter D

    Vapour cools high in the sky and turns into tiny drops. The drops make the cloud, at D.

    • If you chose A: A is where rain falls from the cloud. Condensation is where the cloud forms.
    • If you chose B: B is the water flowing down the hill to the sea. Condensation is in the sky.
    • If you chose C: C is where water rises from the sea as vapour. That is evaporation. Go to S2.4.4.

  8. Kofi says today's rain is new water, made in the clouds. Is he right?

    Tap your answer.

    1. Yes, that is right. The same water goes round the water cycle again and again. It is not made new or used up.

    2. Not this one. Clouds do not make water. They hold water that rose from the sea and the land. Try another.

    3. Not this one. Rain is not used up. It flows to the sea, rises again and falls again. Try another.

    See the answer

    No. It is water that has gone round and round.

    The same water goes round the water cycle again and again. It is not made new or used up.

    • If you chose B: Clouds do not make water. They hold water that rose from the sea and the land.
    • If you chose C: Rain is not used up. It flows to the sea, rises again and falls again.

Keep it

Copy this into your exercise book.

The Sun's heat makes water evaporate. The vapour cools into drops. They make clouds. Rain falls and rivers flow to the sea. The same water goes round and round.

Draw: Sea, Sun, cloud and arrows going round. Write the four steps.

S2.4.7 Chapter 7

Clean water

If water looks clear, is it safe to drink?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

  • You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

Mei has a jar of muddy water. She wants to clean it. Can a cloth do the job?

Draw it first

Draw a cloth filter

  1. A cup with a cloth tied over its top, labelled cloth. An arrow brings muddy water, labelled muddy water, down onto the cloth. Bits of sand, labelled sand, stay on top of the cloth. Drops of water drip through into the cup. The water in the cup is labelled filtered water.cloth

    1 Draw a cup. Tie a cloth over its top. Write cloth.

  2. A cup with a cloth tied over its top, labelled cloth. An arrow brings muddy water, labelled muddy water, down onto the cloth. Bits of sand, labelled sand, stay on top of the cloth. Drops of water drip through into the cup. The water in the cup is labelled filtered water.clothmuddy watersand

    2 Pour muddy water on the cloth. The sand stays on top. Write muddy water and sand.

  3. A cup with a cloth tied over its top, labelled cloth. An arrow brings muddy water, labelled muddy water, down onto the cloth. Bits of sand, labelled sand, stay on top of the cloth. Drops of water drip through into the cup. The water in the cup is labelled filtered water.clothmuddy watersandfiltered water

    3 Water drips into the cup. Write filtered water.

Muddy water has bits in it. The bits are sand and soil. You can see them. They do not dissolve. To dissolve is to mix into water. The pieces get too small to see.

Salt and sugar dissolve. Sand does not.

A filter has tiny holes. Water goes through the holes. Bigger bits stay behind. A cloth is a filter.

The holes in the cloth are too small for sand. They are big enough for water. So the sand stays on the cloth.

Now stir salt into water. The salt seems to vanish. It has dissolved. It broke into pieces too small to see. They are mixed all through the water.

Pour the salty water through a cloth. The salt goes through with the water. Its pieces are far smaller than the holes. Sugar does the same.

See it three ways

As a picture

Two pictures of a cloth, labelled cloth. On the left, labelled sand, bits of sand sit on top of the cloth and stay there. Only water goes through, shown by an arrow. The words under it are stays on top. On the right, labelled salt, dots of salt are above and below the cloth, and arrows go to the cloth and through it. The words under it are goes through.sandsaltclothstays on topgoes through

In words

Sand is bits you can see. The cloth holds them back. Salt dissolves into pieces too small to see. They go through the cloth with the water.

Water can hold germs too. Germs are living things so small that you cannot see them. Some germs make people ill. They are small enough to go through a cloth. So clear water can still have germs in it.

On the left, a glass of clear water, labelled clear water. Lines lead from it to a big circle on the right, a close up of the water. Inside the circle are a few small circles, which are germs, and a few small black squares, which are salt dissolved in the water. A key under the circle names them: germs and salt. Labels: clear water, germs, salt.clear watergermssalt
Clear water can hold germs and salt. You cannot see them.

Try it

Filter sand, then test salt

You need: two cups, a clean cloth and string, a spoon of sand, a spoon of salt, water, a saucer, a sunny place.

Be safe: Never drink or taste the water in this activity.

  1. Stir a spoon of sand into a cup of water.
  2. Tie a clean cloth over the mouth of the second cup.
  3. Pour the sandy water slowly onto the cloth.
  4. Look at the cloth. Look at the water in the cup.
  5. Wash both cups and the cloth. Stir a spoon of salt into a cup of clean water. Wait until the salt is out of sight.
  6. Tie the cloth over the other cup. Pour the salty water through it.
  7. Pour a little of it onto a saucer. Put the saucer in the sun.
  8. When the saucer is dry, look at it.

What you will see: The cloth holds back the sand. The water in the cup has no sand. The salty water goes through the cloth too. When the saucer dries, a white crust is left. It is salt. The salt went through the cloth with the water. Only the water rose into the air.

If you cannot try it, this is what happens.
Two saucers. The saucer on the left holds salt water, labelled salt water. An arrow points to the saucer on the right, with the word dries above the arrow. The saucer on the right has white crumbs in it, labelled salt is left.salt waterdriessalt is left

Only the water rises. The salt stays behind. So rain is not salty, even when it came from the sea.

A pot of dotted water with open round bubbles all through it, labelled pot and bubbles. Three arrows rise from the water, labelled water vapour. Small black squares of salt are spread all through the water, labelled salt stays in the water. Labels: water vapour, pot, salt stays, in the water, bubbles.water vapourbubblespotsalt staysin the water
Boiling kills germs. The water rises, and the salt stays.
Four boxes joined by arrows, in order: muddy water, cloth, boil, cool. Each arrow points to the next box. Labels: muddy water, cloth, boil, cool.muddy waterclothboilcool
A cloth takes out sand. A grown up boils the water. Then it cools.

A wrong idea many people have

If water is clear, it is safe to drink.

Why it feels right: Dirty water looks muddy. So water that looks clear must be clean.

The test that breaks it: Stir salt into water until it looks clear. Pour it through a cloth. It stays clear. Dry a little in a saucer in the sun. White salt is left. Clear water can hold things you cannot see. Do not taste it.

What is true: Clear water can hold salt, sugar and germs. A cloth does not take them out. A grown up must boil water before anyone drinks it.

Key words

filter
something with tiny holes. Water goes through. Bigger bits stay behind.
dissolve
to mix into water in pieces too small to see.
germs
living things too small to see. Some make people ill.

Back to your guess

The answer is D: No. Clear water can still hold germs.

Clear water is not always safe. A cloth holds back sand and mud. It does not stop germs. A grown up must boil water before anyone drinks it.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Which of these does a cloth filter hold back?

    Tap your answer.

    1. Yes, that is right. The holes are too small for sand. They are big enough for water, dissolved salt and germs.

    2. Not this one. Dissolved salt is in pieces too small to see. They pass through the cloth. Try another.

    3. Not this one. Germs are tiny. They go through the holes in a cloth. Try another.

    See the answer

    Sand

    The holes are too small for sand. They are big enough for water, dissolved salt and germs.

    • If you chose B: Dissolved salt is in pieces too small to see. They pass through the cloth.
    • If you chose C: Germs are tiny. They go through the holes in a cloth.

  2. Ravi pours salty water through a cloth. Is the salt still in the water?

    Tap your answer.

    1. Not this one. A cloth holds back only bits you can see. Dissolved salt is too small. Try another.

    2. Not this one. Dissolved salt is still salt. Dry a little of the water and white salt is left. Try another.

    3. Yes, that is right. The salt broke into tiny pieces. They go through the holes with the water. A dried saucer shows the salt.

    See the answer

    Yes. Dissolved salt goes through the cloth.

    The salt broke into tiny pieces. They go through the holes with the water. A dried saucer shows the salt.

    • If you chose A: A cloth holds back only bits you can see. Dissolved salt is too small.
    • If you chose B: Dissolved salt is still salt. Dry a little of the water and white salt is left.

  3. Tariq filters muddy water through a cloth. It looks clear. What must a grown up do before anyone drinks it?

    Tap your answer.

    1. Not this one. Clear water can hold germs. A cloth does not take them out. Try another.

    2. Not this one. A cloth cannot stop germs, so a second go does not help. Boiling kills them. Try another.

    3. Not this one. Standing lets mud sink. The germs stay in the water. Try another.

    4. Yes, that is right. A cloth holds back sand. It does not stop germs. Boiling kills germs.

    See the answer

    Boil it hard, then let it cool.

    A cloth holds back sand. It does not stop germs. Boiling kills germs.

    • If you chose A: Clear water can hold germs. A cloth does not take them out.
    • If you chose B: A cloth cannot stop germs, so a second go does not help. Boiling kills them.
    • If you chose C: Standing lets mud sink. The germs stay in the water.

  4. Salty water goes through a cloth. A grown up then boils it. Is the salt gone?

    Tap your answer.

    1. Not this one. Only the water rises as vapour. The salt stays in the pot. Try another.

    2. Yes, that is right. The water becomes vapour. The salt stays behind in the pot.

    3. Not this one. A cloth cannot take out dissolved salt. It goes through with the water. Try another.

    See the answer

    No. Boiling kills germs but leaves the salt.

    The water becomes vapour. The salt stays behind in the pot.

    • If you chose A: Only the water rises as vapour. The salt stays in the pot.
    • If you chose C: A cloth cannot take out dissolved salt. It goes through with the water.

  5. From an earlier chapter

    Sand, water and steam. Which one is a liquid?

    Tap your answer.

    1. Yes, that is right. A liquid takes the shape of its cup. Its amount stays the same. Water is a liquid.

    2. Not this one. Sand is made of hard grains. It is a solid. Go to S2.4.1. Try another.

    3. Not this one. Steam is water vapour. That is water as a gas. Go to S2.4.4. Try another.

    See the answer

    Water

    A liquid takes the shape of its cup. Its amount stays the same. Water is a liquid.

    • If you chose B: Sand is made of hard grains. It is a solid. Go to S2.4.1.
    • If you chose C: Steam is water vapour. That is water as a gas. Go to S2.4.4.

  6. Draw a cloth filter. Show where the sand stays and where the water goes.

    See the answer

    A cup with a cloth over it. The sand sits on top of the cloth. Water drips through into the cup.

    The holes in the cloth are too small for sand. They let the water through.

  7. Water from a stream is clear and cold. Can you tell by looking if it is safe?

    Tap your answer.

    1. Not this one. Clear water can hold germs and salt. You cannot see them. Try another.

    2. Yes, that is right. You cannot see germs or dissolved salt. A grown up must boil the water before anyone drinks it.

    3. Not this one. Never taste water to test it. You cannot taste or smell most germs. Try another.

    See the answer

    No. Germs are too small to see.

    You cannot see germs or dissolved salt. A grown up must boil the water before anyone drinks it.

    • If you chose A: Clear water can hold germs and salt. You cannot see them.
    • If you chose C: Never taste water to test it. You cannot taste or smell most germs.

  8. Ravi stirs sugar into water until it vanishes. Where is the sugar?

    Tap your answer.

    1. Not this one. Dissolved sugar is still sugar. Dry some of the water and the sugar comes back. Try another.

    2. Not this one. Nothing is lost. The sugar is in the water, in pieces too small to see. Try another.

    3. Yes, that is right. Sugar dissolves into tiny pieces that mix all through the water. They are still there.

    See the answer

    It is in the water, in pieces too small to see.

    Sugar dissolves into tiny pieces that mix all through the water. They are still there.

    • If you chose A: Dissolved sugar is still sugar. Dry some of the water and the sugar comes back.
    • If you chose B: Nothing is lost. The sugar is in the water, in pieces too small to see.

Keep it

Copy this into your exercise book.

A cloth filter holds back sand and mud. Salt and sugar dissolve, so they go through. A cloth does not stop germs. Clear water is not always safe. A grown up must boil water before anyone drinks it.

Draw: A cup with a cloth on top. Sand on the cloth. Drops in the cup.

Key words, A to Z

Every key word in this book, what it means, and the chapter that teaches it.

air
the gas all around us. S2.4.2
boiling
water bubbling hard all the way through. It happens only when water is very hot. S2.4.4
cloud
tiny drops of water, or bits of ice, high in the air. S2.4.6
condensation
water vapour turning back into liquid on something cold. S2.4.5, S2.4.6
container
a thing that holds something, such as a cup. S2.4.1
dew
tiny drops of water on cool grass and leaves at night. S2.4.5
dissolve
to mix into water in pieces too small to see. S2.4.7
evaporation
water turning into water vapour. S2.4.4, S2.4.6
filter
something with tiny holes. Water goes through. Bigger bits stay behind. S2.4.7
freezing
a liquid turning into a solid. Cooling makes it happen. S2.4.3
gas
spreads out to fill any container. S2.4.1
germs
living things too small to see. Some make people ill. S2.4.7
liquid
takes the shape of its container. The amount stays the same. S2.4.1
melting
a solid turning into a liquid. Heat makes it happen. S2.4.3
solid
keeps its own shape. S2.4.1
space
the room that a thing takes up. S2.4.2
temperature
how hot or cold something is. S2.4.3
water cycle
the way water goes from the sea to the sky and back. S2.4.6
water vapour
water as a gas. You cannot see it. S2.4.4, S2.4.5
wind
air that moves. S2.4.2