Chapter 3 of 8

All 8 chapters
  1. 1What magnets pull, readunderstood
  2. 2North and south poles, readunderstood
  3. 3Magnetic force through things, readunderstood
  4. 4Making a compass, readunderstood
  5. 5Electricity: safe and unsafe, readunderstood
  6. 6A simple circuit, readunderstood
  7. 7Conductors, insulators and switches, readunderstood
  8. 8Circuit drawings, readunderstood

S2.8.3 Chapter 3

Magnetic force through things

Can a magnet pull through paper or water?

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

  • Test if a magnet works through paper, cloth, water and wood
  • Compare magnets by counting the pins or clips each one holds

A magnet can pick up a clip without touching it. Can it pull through paper? Through water?

A force is a push or a pull. The pull of a magnet is the magnetic force.

Magnetic force goes through paper. It goes through cloth, water and wood. It goes through air too.

Draw it first

Draw a pull through paper

  1. A clip, labelled clip, lies on a sheet of paper, labelled paper. A magnet, labelled magnet, is under the sheet. An arrow goes down from the clip, through the paper, toward the magnet.clippaper

    1 Draw a sheet of paper. Put a clip on top. Write clip and paper.

  2. A clip, labelled clip, lies on a sheet of paper, labelled paper. A magnet, labelled magnet, is under the sheet. An arrow goes down from the clip, through the paper, toward the magnet.clippapermagnet

    2 Draw a magnet under the paper. Write magnet.

  3. A clip, labelled clip, lies on a sheet of paper, labelled paper. A magnet, labelled magnet, is under the sheet. An arrow goes down from the clip, through the paper, toward the magnet.clippapermagnet

    3 Draw an arrow from the clip to the magnet. The pull goes through the paper.

The pull gets weaker as the gap gets wider. A thick pile of cloth keeps the clip far from the magnet. Then the pull can be too weak.

The same small magnet twice, each labelled magnet, with a clip under each. In the first picture the clip is 1 cm below the magnet, labelled 1 cm, and the word jumps is under it. In the second picture the clip is 6 cm below the magnet, labelled 6 cm, and the words stays still are under it. Labels: magnet, clip, 1 cm, 6 cm, jumps, stays still.magnet1 cmclipjumpsmagnet6 cmclipstays still
For this magnet, a clip 1 cm away jumps. A clip 6 cm away stays still. A weaker magnet needs a smaller gap.

Some magnets are stronger than others. The strength of a magnet is how hard it pulls.

To compare magnets, count the clips each one holds. A stronger magnet holds more clips.

A big magnet is not always strong. A small one can hold more clips. Do not trust the size. Count the clips.

Make it a fair test. Use the same clips each time. Dip each magnet into the same pile.

See it three ways

As a picture

Two magnets, each with a stack of small clips hanging under it. The first magnet, labelled weak, holds a stack of 2 clips, labelled 2 clips. The second magnet, labelled strong, holds a stack of 5 clips, labelled 5 clips.weak2 clipsstrong5 clips

In words

A strong magnet holds more clips than a weak one. Count the clips to compare.

In symbols

Weak: 2 clips. Strong: 5 clips. 5 is more than 2.

Try it

Does the pull go through?

You need: a magnet, a paper clip, a sheet of paper, a piece of cloth, a thin piece of wood, a plastic cup with a little water in it, a second magnet, if you have one.

Be safe: Use a plastic cup, not glass. Keep the magnets away from phones and bank cards. If you have no magnet, look at the result picture.

  1. Lay the clip on the paper. Hold the magnet under the paper.
  2. Move the magnet. Does the clip follow?
  3. Do the same with the cloth and with the wood.
  4. Put the clip in the cup of water. Hold the magnet under the cup.
  5. Dip each magnet into a pile of clips. Count the clips each one holds.

What you will see: The clip follows the magnet through the paper. It does the same through the cloth, the wood and the water. The magnet does not need to touch it. Thick wood may make the gap too wide. With two magnets, the one that holds more clips is stronger.

If you cannot try it, this is what happens.
Four small pictures, each with a magnet at the bottom. In three, a clip lies on a layer, labelled paper, cloth and wood. In the fourth, the clip lies in water, labelled water. In every picture the magnet holds the clip through the layer. Labels: clip, magnet, paper, cloth, wood, water.clipmagnetpaperclipmagnetclothclipmagnetwoodclipmagnetwater

A wrong idea many people have

A magnet works only when it touches something.

Why it feels right: A magnet sticks to a nail when they touch.

The test that breaks it: Lay a clip on a table. Slowly bring a magnet close. Do not touch it. The clip jumps to the magnet from a little way off. Now lay paper over the clip. Hold the magnet over the paper. The clip still comes up.

What is true: A magnet pulls across a gap. The pull goes through paper, cloth, water and wood. It gets weaker as the gap grows.

Key words

force
a push or a pull.
magnetic force
the pull of a magnet. It goes through paper, cloth, water and wood.
strength
how hard a magnet pulls. Count clips to compare.

Back to your guess

The answer is A: Yes. The pull goes through paper, cloth, water and wood.

The pull goes through paper, cloth, water and wood. It gets weaker as the gap gets wider.

Check yourself

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

  1. A clip is in a cup of water. A magnet is held at the side of the cup. What happens?

    Tap your answer.

    1. Not this one. Magnetic force goes through water. The clip moves. Try another.

    2. Not this one. A magnet pulls a clip. It does not push it away. Go to S2.8.2. Try another.

    3. Yes, that is right. The pull goes through the cup and the water.

    See the answer

    The clip moves toward the magnet.

    The pull goes through the cup and the water.

    • If you chose A: Magnetic force goes through water. The clip moves.
    • If you chose B: A magnet pulls a clip. It does not push it away. Go to S2.8.2.

  2. Magnet A holds 3 clips. Magnet B holds 7 clips. How many more clips does B hold?

    Tap your answer.

    1. Not this one. You added. To find how many more, take 3 away from 7. Try another.

    2. Yes, that is right. 7 take away 3 is 4. B holds 4 more clips, so B is stronger.

    3. Not this one. 7 is how many clips B holds. It is not how many more. Take 3 from 7. Try another.

    See the answer

    4 more

    7 take away 3 is 4. B holds 4 more clips, so B is stronger.

    • If you chose A: You added. To find how many more, take 3 away from 7.
    • If you chose C: 7 is how many clips B holds. It is not how many more. Take 3 from 7.

  3. Look at the picture. Which magnet is stronger?

    Two magnets, A and B. Magnet A holds a stack of 3 small clips. Magnet B holds a stack of 6 small clips. Labels: A, B.AB
    Tap your answer.

    1. Not this one. A holds fewer clips. The magnet that holds more is stronger. Try another.

    2. Yes, that is right. B holds 6 clips. A holds 3. The magnet that holds more clips is stronger.

    3. Not this one. They hold different numbers of clips. So one is stronger. Try another.

    See the answer

    B

    B holds 6 clips. A holds 3. The magnet that holds more clips is stronger.

    • If you chose A: A holds fewer clips. The magnet that holds more is stronger.
    • If you chose C: They hold different numbers of clips. So one is stronger.

  4. Does a magnet have to touch a clip to pull it?

    Tap your answer.

    1. Yes, that is right. Magnetic force acts across a gap. It gets weaker as the gap grows.

    2. Not this one. A magnet can pull a clip from a little way off. It can pull through paper. Try another.

    3. Not this one. Every magnet pulls across a gap. A weak magnet pulls across a small gap. Try another.

    See the answer

    No. The pull works across a gap.

    Magnetic force acts across a gap. It gets weaker as the gap grows.

    • If you chose B: A magnet can pull a clip from a little way off. It can pull through paper.
    • If you chose C: Every magnet pulls across a gap. A weak magnet pulls across a small gap.

  5. From an earlier chapter

    Two S poles are held close. What happens?

    Tap your answer.

    1. Not this one. S and S are like poles. Like poles push apart. Go to S2.8.2. Try another.

    2. Not this one. Two magnets always act on each other when they are close. Go to S2.8.2. Try another.

    3. Yes, that is right. Like poles repel.

    See the answer

    They push apart.

    Like poles repel.

    • If you chose A: S and S are like poles. Like poles push apart. Go to S2.8.2.
    • If you chose B: Two magnets always act on each other when they are close. Go to S2.8.2.

  6. How would you test if a magnet pulls through a cloth?

    See the answer

    Lay a clip on the cloth. Hold the magnet under the cloth. If the clip moves, the pull goes through.

    The magnet does not touch the clip. If the clip moves, the force passed through the cloth.

  7. Look at the picture. One magnet is big and one is small. Which is stronger?

    A big magnet, labelled big, holds a stack of 2 small clips. A small magnet, labelled small, holds a stack of 4 small clips. Labels: big, small.bigsmall
    Tap your answer.

    1. Not this one. Size does not decide. The small magnet holds more clips, so it is stronger. Try another.

    2. Not this one. Magnets differ in strength. Count the clips each one holds. Try another.

    3. Yes, that is right. The magnet that holds more clips is stronger. A big magnet is not always strong.

    See the answer

    The small one, because it holds more clips.

    The magnet that holds more clips is stronger. A big magnet is not always strong.

    • If you chose A: Size does not decide. The small magnet holds more clips, so it is stronger.
    • If you chose B: Magnets differ in strength. Count the clips each one holds.

  8. Look at the picture. A magnet is under a thick pile of cloth. The clip does not move. Why?

    A clip lies on top of a thick pile of cloth, labelled thick cloth. A magnet, labelled magnet, is under the pile. Labels: clip, thick cloth, magnet.clipmagnetthick cloth
    Tap your answer.

    1. Yes, that is right. The pull gets weaker as the gap grows. A thick pile keeps the clip too far away.

    2. Not this one. Cloth lets the pull through. A thin cloth does not stop the clip. Try another.

    3. Not this one. A magnet pulls across a gap. The gap here is too wide for this magnet. Try another.

    See the answer

    The gap is wide, so the pull is too weak.

    The pull gets weaker as the gap grows. A thick pile keeps the clip too far away.

    • If you chose B: Cloth lets the pull through. A thin cloth does not stop the clip.
    • If you chose C: A magnet pulls across a gap. The gap here is too wide for this magnet.

  9. Tariq wants a fair test of two magnets. What should he do?

    Tap your answer.

    1. Not this one. Clips of two sizes make the test unfair. Use the same clips each time. Try another.

    2. Not this one. Each magnet needs the same try. One dip each, in the same pile. Try another.

    3. Not this one. Looks are not a test. Count the clips each magnet holds. Try another.

    4. Yes, that is right. A fair test changes one thing only. Here only the magnet changes.

    See the answer

    Dip each magnet into the same pile of the same clips.

    A fair test changes one thing only. Here only the magnet changes.

    • If you chose A: Clips of two sizes make the test unfair. Use the same clips each time.
    • If you chose B: Each magnet needs the same try. One dip each, in the same pile.
    • If you chose C: Looks are not a test. Count the clips each magnet holds.

  10. Which things let the pull of a magnet go through?

    Tap your answer.

    1. Not this one. Paper, cloth and wood are not clear. The pull goes through them too. Try another.

    2. Not this one. Water and wood let the pull through too. Only a wide gap makes it too weak. Try another.

    3. Not this one. A magnet pulls across a gap. It pulls through many things. Try another.

    4. Yes, that is right. The pull goes through all of them. It gets weaker as the gap grows.

    See the answer

    Paper, cloth, water and wood.

    The pull goes through all of them. It gets weaker as the gap grows.

    • If you chose A: Paper, cloth and wood are not clear. The pull goes through them too.
    • If you chose B: Water and wood let the pull through too. Only a wide gap makes it too weak.
    • If you chose C: A magnet pulls across a gap. It pulls through many things.

Keep it

Copy this into your exercise book.

The pull of a magnet goes through paper, cloth, water and wood. It gets weaker as the gap grows. A stronger magnet holds more clips. Count the clips to compare.

Draw: A clip on paper. A magnet under it. An arrow between them.

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

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