# Magnetising a needle with static electricity using silk cloth

A nautical navigation textbook on my table says that we can magnetise a non-magnetised needle by rubbing it with a silk cloth. I decided to cross check on the internet, and found some experts calling it off as bullshit. They said that it will make the needle charged with static electricity, as the friction will cause the electrons to transfer between surfaces, and the force of a magnetic field does not affect a static object. So if any of you can conform/reject this notion, then please do.

Apart from that, I tried to make sense of the fact that a capacitor creates an instantaneous current when connected to ground. I also know that a magnet can be made by placing a ferrous demagnetised object in the center of a copper coil that has an electric current running through it.

So if we're stranded at sea with our compass demagnetised, can't we make use of two dissimilar materials by rubbing them, then connecting the resultant static charged object to a copper coil that is ground, placing a demagnetised needle in the center of the coil and finally, closing the switch to let the charged object discharge?

As a needle has such low volume and mass, I believe a few such discharging cycles could effectively find us north again!

Will this work?

[EDIT #1] User @abel has noticed a very sweet phenomenon, and I thought it deserves some visual demonstration. I'll try my best to explain it, but any corrections are welcome.

When two objects have opposite electrostatic charge, they arrange their opposite charges as near to each other's opposite charges as physically possible. Thus, regardless of the two objects' orientations, the charges always stay close to each other. If we were to turn an object (say, a needle) near the surface of another oppositely charged object (say, silk cloth), we effectively move the charges relative to the object (needle) because the charges don't move and the object (needle) does! This imitates the electromagnet coil, when the charges (electrons) in the coil move around the core magnet in the center. I drew these diagrams, dedicated to Sir @abel and for future viewers of this post.

Rolling the (-) charged needle on a (+) charged (flat) silk cloth...

This is a cross section view. The needle's negative charged excess electrons attract the positive particles in the silk cloth. The like charges are repelled away from the points of contact...

Despite turning the needle to the right, it's electrons stay in the same place, which can be thought of as the electrons turning to the left of the yellow point on a stationary needle! The electrons are moving around the needle, just like the electrons in an electromagnetic coil move around the core magnet!

Turned needle...

Needle's charges (electrons) represented by cyan circle...

Needle's charges (electrons) can be thought of as having turned left of needle's yellow point...

• Get a non-magnetised needle and a silk cloth, test and let us know the results. Nov 13, 2021 at 9:41
• If you get enough charge to travel fast enough in a loop it might work. Alternatively, moving the needle sideways against the charged object, always in the same direction. Might be some technique to it. Do try it and report back, I am somewhat curious. The other method, per folklore, is striking needle with a hammer while pointing North/South. Nov 13, 2021 at 14:01
• @pete-w Are you telling me that decades (perhaps centuries) of nautical instruction, meant to save your very life at sea, has got us a method to magnetise that science has yet to prove? Come on. Life isn't that worthless... Nov 14, 2021 at 9:02
• @solar-mike If I do try, I can't be sure if the needle was already magnetised by the electrical monstrosities our house has. I really hope there's a purely scientific approach to this. I mean science at this basic level is (should be) pretty solid and universal, and shouldn't require us to test this "hypothesis". Am I right? Nov 14, 2021 at 9:05
• @pete-w I didn't mean to offend you brother, so I hope that's not what happened. I agree with what you said, but find it strange that nobody ever bothered to actually prove this and sailors just carried on using it like as if it "just works". Nov 15, 2021 at 0:16

## 3 Answers

I believe the method mentioned involves rolling said needle on a charged cloth.

Even if both the needle and the cloth become charged, the key is to not discharge them. As you roll the needle, the charge flows around it, causing the same effect as flowing electricity through coils around a stationary needle.

The key is not in if but in how. Depends is an answer for a lot.

• Please elaborate brother. A very rough visual diagram will do me a lot of good. Represent the needle as a line and just demonstrate the rolling phenomenon you say. Nov 16, 2021 at 0:49
• fill a bottle halfway with water and roll it. bottle is the needle. gravity is the electric field from the charged cloth. water (higher density) is the charge attracted by the charged cloth, while air is the one repelled.
– Abel
Nov 16, 2021 at 0:53
• I am now in more confusion than I started with haha :D. So you're saying that if we manage to roll the needle, we CAN magnetise it? This is a very good observation by the way, a very good one indeed. Nov 16, 2021 at 23:23
• Also, what if we used a hand crank triboelectric generator like the one with a glass flywheel that has a leather flap pressed against it. Will magnetisation using the rolling method require lesser energy than using a triboelectric generator? I guess yes, because there will be a greater heat loss in the triboelectric generator than simply rolling the needle against a charged cloth? Nov 16, 2021 at 23:33
• check the edit, but don't forget to read the last two comments! Nov 17, 2021 at 1:48

Your idea is remotely possible but not practical. "Possible" because, surprisingly, I once saw an iron rod several feet long get magnetized by getting struck on an end while it was held in an NS direction. It was able to pick up iron filings. I can't imagine how you'd find a capacitor, or a length of suitable wire to do what you suggested.

An accurate compass isn't essential for lifeboat navigation. NSEW directions in daytime can be determined by the altitude/azimuth of the sun. A dab hand (with a watch) can do it. At night, stars suffice. You don't need to be very accurate.

The textbook section that started you thinking is wrong. I doubt you found anything online, from a reputable source, that says otherwise. "Reputable source" might be hard to find these days. There are some that say a person could be magnetized by a vaccine injection.

• Vaccine injection magnetisation gets too far imho, but the need for a compass in navigation is essential. What if it's cloudy and you can't see the sun/stars? I know it's highly unlikely to be cloudy 24/7 but as a sailor, you must be ready for every possibility. And plus, the time it takes to calculate your position from sun/stars can get you off direction by a teeny tiny bit. A compass is real-time direction, so a fool-proof magnetisation without a magnet/battery in the first place would help. Nov 16, 2021 at 23:16

The method sounds questionable. A compass needle needs to have a defined North and South magnetization. Does the method define exactly how to assure this? Bear in mind that the north geographic pole of the earth has a south magnetic pole (albeit offset by a few degrees); the north pointing end of the needle needs to be magnetized as a north pole. If these details are not in the nautical manual then it is better to just carry a backup compass.

• Yes, these details are quite obvious I think. But for now, let's focus on whether we can achieve magnetisation at all, not on whether we can make sense of the needle once its magnetised. Nov 16, 2021 at 0:47