Chapter 4 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

S2.8.4 Chapter 4

Making a compass

How does a compass know where north is?

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

  • Make a compass from a magnetised needle floating on water
  • Explain that a compass needle points north and south

A compass is a tool that shows you which way is north. Inside it is a thin magnet that can turn.

You can make one. First you must magnetise a needle. This means to make it a magnet.

Stroke the needle with one end of a magnet. Stroke it many times. Always stroke the same way. Lift the magnet away at the end of each stroke.

Next, float the needle. Lay it on a leaf or paper. Float that on still water. The leaf holds it up. The needle can turn freely.

Draw it first

Draw how to make a compass

  1. Three pictures. First, a magnet, labelled magnet, is slid along a needle, labelled needle, in one direction. An arrow is labelled one way. Second, a needle, labelled needle, lies on a leaf, labelled leaf, floating on water, labelled water. Third, a compass dial with the letters N, E, S and W and a needle in the middle. Labels: magnet, one way, needle, leaf, water, N, E, S, W.magnetone wayneedle

    1 Draw a magnet sliding along a needle, one way. Write magnet, needle and one way.

  2. Three pictures. First, a magnet, labelled magnet, is slid along a needle, labelled needle, in one direction. An arrow is labelled one way. Second, a needle, labelled needle, lies on a leaf, labelled leaf, floating on water, labelled water. Third, a compass dial with the letters N, E, S and W and a needle in the middle. Labels: magnet, one way, needle, leaf, water, N, E, S, W.needleleafwater

    2 Draw the needle on a leaf on water. Write needle, leaf and water.

  3. Three pictures. First, a magnet, labelled magnet, is slid along a needle, labelled needle, in one direction. An arrow is labelled one way. Second, a needle, labelled needle, lies on a leaf, labelled leaf, floating on water, labelled water. Third, a compass dial with the letters N, E, S and W and a needle in the middle. Labels: magnet, one way, needle, leaf, water, N, E, S, W.NESW

    3 Draw a circle with N, E, S and W. Draw the needle inside it.

Wait. The needle turns slowly. Then it stops. One end points north. The other end points south.

In our pictures, the black half points north, to N. The white half points south, to S. On a real compass the north end may be red.

A compass dial with the letter N at the top, E on the right, S at the bottom and W on the left. The needle has a black half that points up to N and a white half that points down to S. Labels: N, E, S, W.NESW
The black half points north, to N. The white half points south, to S.

Why? The Earth acts like a giant magnet. The needle is a small magnet. It lines up with the Earth.

The needle points roughly north and south. In many places it is a little off true north. It is still near enough to find your way.

See it three ways

As a picture

The Earth, drawn as a circle labelled Earth. A dashed line runs through it, with the label north at the top and the label south at the bottom. Beside it is a needle, labelled needle, lined up with the dashed line.northEarthsouthneedle

In words

The Earth acts like a giant magnet. A needle lines up with it. One end points north. The other end points south.

A compass works in most places on Earth. Turn round, and the needle still points the same way.

Try it

Make a compass

You need: a sewing needle, a magnet, a leaf or a scrap of paper, a bowl of still water, a grown up to help.

Be safe: A needle is sharp. A grown up must help. Never put a needle or magnet in your mouth. If you have no needle or magnet, look at the result picture.

  1. A grown up holds the needle. Put one end of the magnet at the eye of the needle.
  2. Slide the magnet along to the point. Lift it away. Go back through the air.
  3. Do this about 30 times. Always the same way.
  4. Set the bowl where there is no wind. Wait until the water is still.
  5. Lay the leaf on the water. Lay the needle on the leaf.
  6. Wait. Watch the needle turn, then stop.
  7. Turn the bowl. The needle turns back the same way.

What you will see: The needle turns and stops. It points roughly north and south. Turn the bowl and it stops the same way again. One end always points north. Ask a grown up which way north is. Mark that end with a dot. If it does not turn, stroke it more times. Keep other magnets and phones away.

If you cannot try it, this is what happens.
A bowl of water seen from above. A leaf, labelled leaf, floats in the middle. The needle, labelled needle, lies along the leaf. It points straight up and down the page. The label north is at the top and the label south is at the bottom.northsouthleafneedle

A wrong idea many people have

A compass needle always points north, whatever is near it.

Why it feels right: On a walk, a compass shows north every time you look.

The test that breaks it: Float your needle, or lay a compass on a table. Wait until it is still. Now bring a magnet close. The needle turns toward the magnet. Take the magnet away. The needle turns back.

What is true: The Earth pulls the needle only a little. A magnet that is near pulls much harder. Keep a compass away from magnets.

Key words

compass
a tool with a magnet needle that points north and south.
magnetise
to make a thing into a magnet.
needle
a thin piece of steel. Floating, it turns to point north and south.

Back to your guess

The answer is C: A small magnet inside it turns to point north and south.

A compass has a small magnet that can turn. The Earth acts like a giant magnet. The needle lines up with it.

Check yourself

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

  1. How do you magnetise a needle?

    Tap your answer.

    1. Not this one. Strokes the other way undo the work. Stroke one way only. Try another.

    2. Yes, that is right. Many strokes one way line up the needle. It becomes a magnet.

    3. Not this one. Water does not make a magnet. You need to stroke it with a magnet. Try another.

    See the answer

    Stroke it many times one way with a magnet.

    Many strokes one way line up the needle. It becomes a magnet.

    • If you chose A: Strokes the other way undo the work. Stroke one way only.
    • If you chose C: Water does not make a magnet. You need to stroke it with a magnet.

  2. A needle floats on a leaf and stops. Which way does it point?

    Tap your answer.

    1. Yes, that is right. The Earth acts like a giant magnet. The needle lines up with it.

    2. Not this one. A wall does not pull the needle. The Earth acts like a magnet. Try another.

    3. Not this one. The needle does not follow the Sun. It lines up with the Earth. Try another.

    See the answer

    Roughly north and south

    The Earth acts like a giant magnet. The needle lines up with it.

    • If you chose B: A wall does not pull the needle. The Earth acts like a magnet.
    • If you chose C: The needle does not follow the Sun. It lines up with the Earth.

  3. Look at the picture. Which letter does the black half of the needle point to?

    A compass dial with a needle in the middle. The needle has a black half and a white half. The letters N, E, S and W are around the edge. Labels: N, E, S, W.NESW
    Tap your answer.

    1. Not this one. The black half points north, to N. Turn the dial, and the needle still points to N. Try another.

    2. Not this one. S is where the white half points. The black half points north. Try another.

    3. Not this one. The black half points north, to N. Try another.

    4. Yes, that is right. The black half of a compass needle points north. The dial turns, but the needle still points to N.

    See the answer

    N

    The black half of a compass needle points north. The dial turns, but the needle still points to N.

    • If you chose A: The black half points north, to N. Turn the dial, and the needle still points to N.
    • If you chose B: S is where the white half points. The black half points north.
    • If you chose C: The black half points north, to N.

  4. Why does a floating needle turn?

    Tap your answer.

    1. Not this one. Water does not push it north. The needle is a small magnet that lines up with the Earth. Try another.

    2. Not this one. The leaf only holds the needle up. It does not turn it. Try another.

    3. Not this one. Wind would push it any way. In still air the needle turns back to the same way. Try another.

    4. Yes, that is right. The needle is a magnet. It lines up with the Earth, so one end points north.

    See the answer

    The Earth acts like a giant magnet.

    The needle is a magnet. It lines up with the Earth, so one end points north.

    • If you chose A: Water does not push it north. The needle is a small magnet that lines up with the Earth.
    • If you chose B: The leaf only holds the needle up. It does not turn it.
    • If you chose C: Wind would push it any way. In still air the needle turns back to the same way.

  5. From an earlier chapter

    Which of these will a magnet pull?

    Tap your answer.

    1. Not this one. Wood is not magnetic. Go to S2.8.1. Try another.

    2. Yes, that is right. A magnet pulls iron and steel. A needle is steel.

    3. Not this one. Plastic is not magnetic. Go to S2.8.1. Try another.

    See the answer

    A steel needle

    A magnet pulls iron and steel. A needle is steel.

    • If you chose A: Wood is not magnetic. Go to S2.8.1.
    • If you chose C: Plastic is not magnetic. Go to S2.8.1.

  6. Write the steps to make a compass.

    See the answer

    Stroke a needle many times one way with a magnet. Lay it on a leaf on still water. Wait. The needle turns to point roughly north and south.

    Stroking makes the needle a magnet. The leaf lets it turn. The Earth lines it up.

  7. Look at the picture. Why does the needle lie on a leaf?

    A bowl of water seen from the side. A leaf, labelled leaf, floats on the water, labelled water. A needle, labelled needle, lies on the leaf. Labels: needle, leaf, water.needleleafwater
    Tap your answer.

    1. Yes, that is right. A steel needle sinks in water. The leaf keeps it afloat, and it can turn.

    2. Not this one. A leaf is not magnetic. Stroking with a magnet makes the needle a magnet. Try another.

    3. Not this one. On the water the leaf lets the needle turn. A needle on a table cannot turn so well. Try another.

    See the answer

    The leaf holds it up, so it can turn freely.

    A steel needle sinks in water. The leaf keeps it afloat, and it can turn.

    • If you chose B: A leaf is not magnetic. Stroking with a magnet makes the needle a magnet.
    • If you chose C: On the water the leaf lets the needle turn. A needle on a table cannot turn so well.

  8. Ravi turns the bowl round. What does the floating needle do?

    Tap your answer.

    1. Not this one. The needle lines up with the Earth, not with the bowl. It turns back to point the same way. Try another.

    2. Not this one. The needle only needs still water. Then it lines up again. Try another.

    3. Yes, that is right. The Earth lines the needle up. The needle points the same way when the bowl turns.

    See the answer

    It turns back and again points roughly north and south.

    The Earth lines the needle up. The needle points the same way when the bowl turns.

    • If you chose A: The needle lines up with the Earth, not with the bowl. It turns back to point the same way.
    • If you chose B: The needle only needs still water. Then it lines up again.

  9. A compass is set down next to a strong magnet. What does the needle do?

    Tap your answer.

    1. Not this one. A near magnet pulls the needle much harder than the Earth. Try another.

    2. Yes, that is right. A near magnet pulls harder than the Earth. Keep a compass away from magnets.

    3. Not this one. Take the magnet away and the needle usually turns back to north. Try another.

    See the answer

    It turns toward the magnet.

    A near magnet pulls harder than the Earth. Keep a compass away from magnets.

    • If you chose A: A near magnet pulls the needle much harder than the Earth.
    • If you chose C: Take the magnet away and the needle usually turns back to north.

  10. Look at the picture. The dial is turned round. Which half of the needle points north?

    A compass dial turned round. The letter N is on the right, E at the bottom, S on the left and W at the top. The needle has a black half and a white half. Labels: N, E, S, W.NESW
    Tap your answer.

    1. Not this one. The white half points south, to S. Try another.

    2. Not this one. The needle keeps its way. The black half always points north, however you turn the dial. Try another.

    3. Yes, that is right. The black half of the needle points north. The white half points south.

    See the answer

    The black half.

    The black half of the needle points north. The white half points south.

    • If you chose A: The white half points south, to S.
    • If you chose B: The needle keeps its way. The black half always points north, however you turn the dial.

Keep it

Copy this into your exercise book.

Stroke a needle many times one way with a magnet. Float it on a leaf on still water. It turns to point roughly north and south. The Earth acts like a giant magnet.

Draw: A bowl of water. A leaf with a needle on it. The words north and south.

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 (707 KB). It opens on any phone.