Earth’s magnetic field guides a compass — Earth science, 7–10 years
Earth acts a little like a giant magnet. Its invisible magnetic field makes a compass needle turn and helps us find directions.
An invisible direction finder
A compass has a tiny magnet that can turn freely. Earth’s magnetic field pulls one end of it towards the north, so the needle settles along a north–south line. We cannot see the field, but we can notice what it does.
Why people needed a compass
Before reliable maps and digital devices, travellers could lose their direction when clouds hid the Sun or when they were far from land. A compass solved this problem by giving a steady reference for north. Earth’s field comes mainly from moving, hot iron deep inside its outer core.
Using a compass on a walk
You stand facing the school gate and want to walk east. First, place the compass flat and wait for the needle to stop. Turn the compass so its north mark matches the needle’s north end. Now east is a quarter-turn to the right of north, so walk that way.
A compass is not magic
A common mistake is to think the needle always points exactly to the place called the North Pole. That seems reasonable because the needle is labelled north, but it actually follows the magnetic field, whose direction is not exactly the same as map north. Metal objects and magnets nearby can also disturb it.
Finding direction in the real world
Compasses are still useful when hiking, sailing or checking a map outdoors. They work without batteries, although you must keep them away from strong magnets and metal equipment. Animals such as some birds can also sense Earth’s magnetic field when migrating.
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