Make a Compass Experiment: Magnetise a Needle at Home

It takes ten seconds to settle, and watching the needle swing, overshoot and come back is better than any diagram of a magnetic field. This make a compass experiment needs a sewing needle, a magnet and a bowl of water, and the result is a real instrument rather than a toy: it genuinely points north, and the direction it picks is not quite the direction a map calls north. That gap has a name, a value you can look up for your own street, and it is the reason this activity is worth an hour instead of ten minutes.

Key Takeaways

• You’ll magnetise a sewing needle by stroking it with a magnet, float it on cork, and watch it align with Earth’s field.
• It teaches that Earth has a magnetic field, that magnetic north is not true north, and that magnetism can be induced in steel.
• Best from about age 7, with an adult handling the needle and the magnet.
• What usually goes wrong: stroking back and forth instead of one way, which leaves the needle unmagnetised.
• Do not use small loose rare-earth magnets with young children. Use one large magnet, held by the adult.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Sewing needle	2–3, 40 mm or longer	Sewing kit	A straightened paperclip, or a steel pin
One large magnet	One, bar magnet or a loudspeaker magnet	School set, or salvaged from a dead speaker	A strong fridge magnet works slowly. Avoid small neodymium discs with young kids
Cork, foam or a bottle cap	A 10 mm disc, 3 mm thick	Wine cork sliced, packaging foam, plastic cap	A small leaf also floats well
Shallow bowl	One, 15–20 cm across	Kitchen	A dinner plate with a rim
Water	Enough for 2 cm depth	Tap	—
Reference compass	One	A phone compass app	Any real compass, or the sun at local noon
Protractor and paper	One each	Pencil case	For measuring the offset from true north

Time: prep 10 min, experiment 30 min, cleanup 5 min Cost: everything is probably in your house, except possibly the magnet Mess level: low

Do the Experiment: The Make a Compass Experiment, Step by Step

Step 1 — Check the needle is not magnetic yet

Float it on the cork in the bowl and watch. An ordinary needle will drift and settle anywhere, with no preferred direction. Turn the bowl and it will not re-point. This baseline makes the later result mean something.

Step 2 — Stroke the needle one way, forty times

An adult holds the magnet. Place one pole at the needle’s eye, drag it smoothly along to the point, then lift the magnet clear of the needle and return it through the air before starting again. Same pole, same direction, forty strokes. Lifting away at the end of each stroke is the entire trick.

Step 3 — Ask for the prediction

Will the needle point north and stop, wobble forever, or point at the nearest metal thing? Get the answer out loud before it goes back in the water.

Step 4 — Float it and watch it settle

Lay the needle across the cork disc, or push it through the disc if it will not balance, and set the disc gently on the water in the middle of the bowl.

What you should see: the disc rotates, swings past its final position, comes back, and settles within about ten seconds. Turn the bowl ninety degrees and the needle will swing back to the same compass heading. That repeatability is the proof.

Step 5 — Check against a real compass, then find the needle’s north end

Put a reference compass or a phone compass app on the table, a hand’s width away, and compare headings. Then test which end of the needle is which by bringing the magnet’s known north pole slowly toward the floating needle: like poles repel.

What you should see: agreement within a few degrees. If it is reversed by 180 degrees, you stroked from point to eye instead of eye to point, which is not a mistake, just a convention.

Step 6 — Measure the offset from true north

Find true north independently: either the shadow of a vertical stick at local solar noon, which runs exactly north-south, or Polaris on a clear night in the northern hemisphere. Mark that line on paper under the bowl, then measure the angle between it and the needle with a protractor.

What you should see: a difference of anything from under a degree to more than twenty, depending on where you live. That angle is magnetic declination, and you can check your measurement against the official value using the NOAA magnetic field calculator with your own latitude and longitude.

What’s Actually Going On

Steel is a hard ferromagnetic material. Inside it, regions called domains each have their magnetic moments aligned, but the domains themselves point in different directions so the whole needle appears unmagnetised. Dragging a magnet’s pole along the needle nudges those domains into agreement, and because hardened steel resists changing back, the alignment persists after the magnet leaves. That is also why the stroking direction matters: rubbing back and forth pushes the domains one way and then the other, undoing your own work. Lift the magnet away at the end of each stroke and every pass contributes.

Once magnetised, the needle is a tiny bar magnet sitting in Earth’s magnetic field. That field is produced by circulating electric currents in the planet’s molten metallic core, not by a lump of permanently magnetised iron, because the core is far hotter than the temperature at which iron loses its magnetism. At the surface the field strength runs between about 0.3 and 0.6 gauss, and the axis of the field is tilted roughly 11 degrees from Earth’s spin axis (HyperPhysics, Georgia State University). Half a gauss is extremely weak. A fridge magnet at its own surface is hundreds of times stronger. That weakness is exactly why the needle has to float: any appreciable friction swamps the torque, which is also why a needle hung on a thread works badly, since the thread’s twist fights back harder than the Earth pulls.

Now the two corrections worth making. First, the needle does not point at the geographic North Pole. It aligns with the horizontal part of the local field, which heads toward the magnetic pole, and the angle between that and true north is the declination. Declination differs from place to place and drifts year by year, which is why the United States and the United Kingdom jointly publish a revised World Magnetic Model every five years (NOAA National Centers for Environmental Information) and why aviation charts have to be reissued. The USGS Geomagnetism Program runs the observatories that feed it.

Second, and this one delights older children: the thing we call Earth’s north magnetic pole is, in magnet language, a south-seeking pole. A compass needle’s north end is attracted to it, and north attracts south. The naming is historical and backwards, and noticing that is a sign someone has actually understood how poles work rather than memorised a label.

How to Explain It to Your Kid

Ages 5–8: The Earth is a giant magnet

Inside the Earth, deep down, something is moving in a way that makes the whole planet act like a magnet. It is a very weak magnet, far weaker than the one in your hand, so the needle has to float on water where nothing can hold it back. Then it slowly turns until it lines up, the way one magnet turns to face another. Let them spin the bowl and watch the needle come back to the same place again and again. That repeat is the part that convinces people.

Ages 9–12: Domains, and north is not north

Introduce domains as small regions inside the steel that each point somewhere, and stroking as the act of lining them up. Then introduce declination with their own measurement. If their needle sits seven degrees off true north, ask what happens to a hiker who walks ten kilometres on that bearing: roughly 1.2 kilometres off target, which is enough to miss a valley. The number makes the idea matter.

Ages 13+: Field strength, torque and why floating is necessary

Give them the numbers. Earth’s surface field of 0.3 to 0.6 gauss is 30 to 60 microtesla, and the torque on a small needle in a field that weak is tiny. Have them estimate it and then compare with the friction of a thread, a pin pivot and a floating cork. Then let them test the dip: suspend a magnetised needle from its exact centre of mass on a thread and look at whether it tilts out of horizontal. It will, by an amount that depends on latitude, and that is the inclination the NOAA calculator also reports.

The question to ask: “If we took this compass to the magnetic north pole, what would the needle do?”

Why Teaching This Early Pays Off

This experiment installs two things at once. The first is that Earth has a field, which is the beginning of understanding aurorae, solar storms, migrating birds and why satellites need radiation shielding. The second is less obvious and more useful: measurement instruments have systematic errors that you can quantify and correct for. A compass is not broken because it points seven degrees off true north. It is a compass, and the seven degrees is a known, tabulated, correctable offset.

That idea generalises far beyond magnetism. Scales drift, clocks run fast, thermometers read high, and the professional response is to characterise the error rather than distrust the instrument. The Framework for K-12 Science Education lists analysing and interpreting data and using mathematics among its core practices for exactly this sort of reasoning (National Research Council, 2012). One afternoon with a needle will not make a child a careful experimentalist. It does give them one concrete memory of a correction that turned a rough instrument into an accurate one.

Before You Start: What Parents Should Know

Best age	7 and up. The declination measurement lands from about 10
Supervision	Adult holds the magnet and does the stroking. Children handle the cork, the bowl and the protractor
Real hazards	Sharp needle point, and a needle dropped on a carpeted floor is genuinely hard to find. Keep a count. Water near electrical items. Magnets wipe bank cards and interfere with pacemakers, so keep them away from wallets and phones
Don’t	Don’t use small loose neodymium discs, balls or cubes, especially with children under eight. Two or more swallowed high-powered magnets attract through the gut wall and often require surgery, which the US Consumer Product Safety Commission states directly. One large magnet an adult keeps hold of, such as a loudspeaker magnet or a classroom bar magnet, does this job better and cannot be swallowed

When It Doesn’t Work

• The needle floats but points nowhere in particular. It is not magnetised. The usual cause is rubbing back and forth. Redo it with forty one-way strokes, lifting the magnet clear through the air after each one, and always with the same pole.
• It points somewhere confidently, but the wrong way. Look for iron near the bowl. A radiator, a steel table frame, a laptop, a speaker or a knife block within half a metre will dominate Earth’s half-gauss field completely. Move to the middle of a wooden table in the middle of a room.
• The cork tips the needle into the water. Use a thinner slice, push the needle through the cork rather than balancing it on top, or switch to a flat piece of packaging foam, which floats more stably than cork.
• It swings and never settles. Surface ripples or a draught. Close windows, let the water sit for a minute before you launch the disc, and use a bowl wide enough that the disc cannot touch the sides, because contact with the rim stops rotation dead.
• The phone compass disagrees with itself. Phone magnetometers need figure-of-eight calibration and are easily confused by the phone’s own speaker magnet and by a case with a magnetic clasp. Treat the phone as the less trustworthy of the two instruments, which is a pleasing result in its own right.

Take It Further

Decay over time: park the compass somewhere undisturbed and retest once a week for a month, recording how long it takes to settle from a 90-degree displacement. Settling time grows as the needle’s magnetisation decays. Then deliberately destroy it: heat a needle on a stove under adult control, or hit it hard twenty times, and retest. Both disrupt domain alignment, and the comparison is a real experiment about why fridge magnets lose strength.

Map the iron in your house: carry the floating compass room to room on a tray, recording the heading every two metres. The deviations map the steel inside your walls and floors. This is a scaled-down version of what geophysical magnetic surveying actually does.

Where This Make a Compass Experiment Sits in a Sequence

Run it after a child has seen a magnetic field drawn out, because “the needle lines up with the field” is a sentence that needs a picture behind it: iron filings around a magnet is the right prerequisite and takes twenty minutes. Afterwards, the declination measurement opens a door into astronomy and navigation rather than more magnetism. Building a sundial that keeps real time requires finding true north, so the two experiments need each other, and making a star wheel to find real constellations gives you Polaris as an independent check. If you want to stay with magnetism, building an electromagnet shows the same effect produced on demand by a current.

What to Watch For Over the Next 3 Months

• Week 4: they ask which way north is before asking which way to go, which is a navigational habit rather than a physics one.
• Month 2: they notice a compass misbehaving near a car or a fridge and diagnose it correctly.
• Month 3: they bring up that the magnetic pole moves, usually after reading something about it, and connect it to why their measured declination had a date attached.

Frequently Asked Questions

Why does stroking have to go one way only?

Each stroke nudges the steel’s magnetic domains into alignment with the direction you are dragging. Rubbing back and forth aligns them one way and then the other, so you finish roughly where you started. Lifting the magnet clear through the air between strokes means every pass adds.

How far off true north should the needle point?

Anywhere from a fraction of a degree to more than twenty, depending on your location, and it changes slowly over the years. Look up the official figure for your coordinates with the NOAA calculator and compare it with your protractor measurement. Agreement within a few degrees is a good result for a cork and a sewing needle.

Can we use a thread instead of water?

You can, and it works poorly. Earth’s field is weak enough that the thread’s resistance to twisting is comparable to the magnetic torque, so the needle settles in the wrong place or not at all. Floating removes almost all friction, which is why every improvised compass uses water.

Will the needle stay magnetised?

For weeks or months, slowly weakening. Heat, sharp knocks and storing it next to another magnet in the wrong orientation all speed up the loss. Re-stroking takes thirty seconds, and measuring how the settling time degrades over a month is one of the better follow-up experiments here.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Nave, R. “Magnetic Field of the Earth.” HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html
2. NOAA National Centers for Environmental Information. “World Magnetic Model.” https://www.ncei.noaa.gov/products/world-magnetic-model
3. NOAA National Centers for Environmental Information. “Magnetic Field Calculators.” https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml
4. U.S. Geological Survey. “Geomagnetism Program.” https://www.usgs.gov/programs/geomagnetism
5. U.S. Consumer Product Safety Commission. “Magnets.” https://www.cpsc.gov/Safety-Education/Safety-Education-Centers/Magnets
6. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. https://doi.org/10.17226/13165