Chapter 2 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

S2.4.2 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

  • Show that air takes up space using a cup pushed into water
  • Show that moving air can push things, such as a paper windmill

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.

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.