When you heat the needle you rearrange the atoms.
Think you understand magnets? In this hands-on activity, use a magnet to make a needle float and then fall.
Safety: This activity uses a lighter and gets very hot. Get an adult to help.
First aid: If you burn yourself, run the burn under cold water for 20 minutes.
There are lots of different types of magnets. Permanent magnets always have a magnetic field. Electromagnets are only magnets when there’s electricity flowing through them. And some objects turn into magnets when they are in a magnetic field.
In an electromagnet, the magnetism is caused by electricity. But in permanent magnets, and in substances that are attracted to magnets (such as iron and some types of steel), the magnetism comes from within. These substances are ferromagnetic.
Sewing needles, such as the one in this activity, are typically made from a type of steel. In a ferromagnetic substance like this, every atom acts as a tiny magnet. Usually, these magnets are pointed in different directions. But a powerful magnet nearby can make all the atoms line up in the same direction, turning all those mini-magnets into one big one.
There are other ways to reorder atoms in iron or steel. When you heat the needle above about 770 °C, the atoms in the metal change into a different pattern. In this new pattern, the iron atoms can’t line up to form a magnet, and it’s no longer attracted to magnetic fields. When it cools down below 770 °C, the pattern changes back and it becomes ferromagnetic again.
If you look at the needle afterwards, it’s probably black, covered in soot. If you carefully wipe the soot off, you might see colours on the needle!
As you heat the steel, it starts to react with the air. A thin layer of oxides will start forming on the outside of the needle. If the layer is only a few atoms thick, it might appear yellowish. As the layer gets thicker it will become more golden, then purple, and then bluish–black.
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