Topsy’s Experiments
The needle that points the way
A compass can help you find your way because its needle always points north. But why does it do that?
What you’ll need
What you’ll need
- A glass
- Water
- Some baking paper
- Scissors
- A pencil
- A pair of compasses (optional)
- A sewing needle
- A magnet (the stronger, the better!)
How to do it
How to do it
Well spotted!
Well spotted!
- The baking paper floats on the water. Once you have placed the needle on the paper, it will adjust to a north-south direction and the paper will move in the water.
- If you rotate the paper with the needle in another direction, the needle will return to the previous position.
Tips
Tips
- If you have a real compass to hand, you can check whether your needle works by observing whether it points in the same direction as the needle in the compass. Remember that the magnet can affect the compass, so keep it at a distance.
- If the needle stops turning, you’ll need to magnetize it again.
What's the secret?
What's the secret?
Imagine that the needle is made up of lots of tiny magnets all jumbled up inside it. By rubbing the needle against the magnet, these tiny magnets all line up to point in the same direction. The magnetic forces are combined so that the needle itself briefly becomes a weak magnet.
Why does the needle rotate? Magnets react to each other. You’ve probably seen how magnets can attract or repel each other. They have two ends – a north pole and a south pole. North repels north, just as south repels south. However, north and south attract each other. The earth itself has a magnetic north pole and a magnetic south pole. This is because the earth’s core contains liquid metal which moves, generating a magnetic field. The magnetized needle responds to the earth’s magnetic field. Since the needle on the baking paper can move freely on the water, it can position itself in the magnetic field in a north-south direction. You can rotate it, but it will move back to point north-south again.
A real compass also has a magnetic needle that can rotate freely in its casing. The needle aligns itself with the earth’s magnetic field and points north.