What it shows
Stroking a steel needle with a magnet turns it into a weak magnet. Floated on water so it can turn freely, the needle lines up north to south, because the Earth itself acts like a giant magnet.
The science
Steel can be made into a magnet because it contains tiny magnetic regions that are normally jumbled. Stroking it in one direction with a magnet, many times, lines these regions up so the needle gets a north and a south pole of its own. The Earth has a magnetic field that runs roughly from south to north, and a free-turning magnet settles along it. The floating cork lets the needle turn with almost no friction, so the needle swings round and points north and south every time, which is how sailors found their way before satellites.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A steel sewing needle
- A bar magnet or a strong fridge magnet
- A small piece of cork, thermocol or a bottle cap to float the needle on
- A bowl of water
- A small pin or paper clip to test the needle
- A marker pen
- A compass app on a phone or a real compass, to check
Safety
For this project: Needles are sharp; an adult must help young children to handle and push the needle into the cork.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Hold the needle by the eye and stroke it from eye to point with one pole of the magnet, lifting the magnet away between strokes, about 40 times.
Check it is magnetised by touching it to a small pin or paper clip; the pin should cling.
Push the needle through a thin slice of cork or lay it on a floating bottle cap, keeping it level.
Float it in the middle of the bowl of water, well away from the sides and any metal objects.
Wait for it to stop turning; it will settle along a north to south line.
Spin the cork gently and watch it return to the same direction each time.
Compare with a phone compass and mark the north-pointing end of the needle with a dot of marker ink.
Bring the bar magnet near and watch the needle swing towards it, then take it away and see it return to north.
What you should see
The floating needle always settles along the same line, matching the north shown by a phone compass, and returns to it after being spun. A nearby magnet pulls it off course.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why does the needle point north?
Because it has become a magnet and the Earth’s magnetic field pulls it into line.
02Why float it on water?
So it can turn freely with very little friction.
03Why stroke the needle in one direction only?
Stroking back and forth would undo the lining up of the tiny magnetic regions.
04What can make a compass give a wrong reading?
Nearby magnets, steel objects or electric wires.
Take it further
Use the compass to draw a map of your school ground, marking which way each building faces.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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