Chapter 1 of 7

All 7 chapters
  1. 1Solids, liquids and gases, readunderstood
  2. 2Air is all around us, readunderstood
  3. 3Melting and freezing, readunderstood
  4. 4Evaporation and drying, readunderstood
  5. 5Condensation, readunderstood
  6. 6The water cycle, readunderstood
  7. 7Clean water, readunderstood

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

  • Sort materials into solids, liquids and gases
  • Describe how each one keeps or changes its shape

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.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (712 KB). It opens on any phone.