Everything you learned about magnetizing a needle is wrong.
Improvised needle compass science

Page two has some great info on magnetizing a needle using a AAA battery, insulated wire, and a drinking straw.

-Blast

Excellent info, thanks.

Good Article. At school aged about 12-13 we were taught how to improvise a compass in Physics class, some folks could even get the needle to float on the dish of water without the paper just using surface tension after magnetising the needle with some insulated coiled wire and a PP3 battery. We were also taught how to make a little electric motor from some magnets, insulted wire, cotton bobbin, battery (making the split ring commutator was always tricky though) etc.

Bear Grylls in his video should have validated his little experiment with a proper compass for the viewers as floating a needle using a dry leaf on water can point in the wrong direction due to wind shear on the leaf, the magnitisation force is very weak as so is not entirely reliable.

Rubbing the needle in the hair is probably just to degrease the needle so as to improve the water surface tension rather than the belief that it is actually magnetising the needle.

The rubbing method would work if when rubbing you heated the needle above the Curie point (about 750-800C for most stainless steels)

I liked the experiment.

While it is a bit off subject I rather liked the look of the wine glasses and lexan with the compas in the middle. would be an intresting center piece. sorry for the "Martha Stuart" home decorating interuption

Well, glad that myth was debunked, cuz I have no hair!!! I really didnt know any of that though...guess what I am doing this weekend???

I like his rigorous approach and am eager to duplicate his results. Wonder if there are other myths that need to be tested...

Well, a fun read. Wonder if IT is a true?

The only one that made sense to me when I was about ten was stroking the needle with a magnet several times in the same direction, and if you had trouble getting it to float, coat the needle with ear wax.

Even as a kid I could tell the difference between static and magnetism.

Sue

I'm still having a hard time with the "everything you read on the Internet isn't true" part.

Excellent post Sheriff Blast. Thanks.

Nice method with electrostatic sparks through the coil to the ground, indeed. And good scientific approach. However, the silk/hair method still have some potential. The fact is - the heavily used sewing needles eventually became magnetic. IMHO, Rob's physics sounds somewhat perfunctory, he is probably just doing something wrong.

The metal thing can not take any static charge by rubbing - nonsense. But you hold the needle in your hand. And the hand - can. The hands static charge will flow off the surface of the needle to the air creating the electric charges motion required to generate the magnetic field. Though, I'm still not sure what causes the proper polarization when you move the needle in one direction along its axis (in solenoid the current must flow perpendicular to the needle in order to achieve the necessary magnetizing effect).

Nice find Blast; thanks.

One of the best statements from the article: "Basically, it's too many people sitting down at typewriters and internet terminals, and not enough people actually doing "dirt-time" and trying this stuff...".

One thing that I do have trouble with if using an improvised compass is how to carry it so you can use it frequently. I'm not one to set it up once an hour while traveling, unless there are really obvious landmarks to anchor my traveling.

The only way to keep it handy that I can think of is to carry it in a cup of water while walking. I want to think there's a better way, but...... ?

Sue

Susan, the better way is needle on a thin string. However it's still better to use landmarks including sun, wind, and clouds movement.

My take home from this thread is to be sure not to damage or lose my compass. Failing that, pray the stars are out at night.

Susan:
The most inaccurate method of all is walking with your nose in your compass. And there is no need to worry about how to carry a floating needle in a cup... (besides, if you rely on surface tension to keep the needle afloat the cup will have to stay still. Any splashing will drown the needle...)

The best way to use a compass is to seek out distant landmarks in the direction you want to travel. Reaching that landmark you check your compass again and aim for a new distant target. Works well in terrain where you have distinct features far away. If you can't see really far this method is a) tedious, b) not so accurate.

If all I have is a floating-needle-in-a-cup, I would check my direction with the compass, find a target in the appropriate direction, put the pin somewhere safe and drink the water. Then I walk to my target, fill up my improvised compass and repeat. There is no need to re-check the compass before I reach my distant target.

It does sound like a fun experiment for the Cub Scouts and Boy Scouts. They will learn a lot about experimenting and have some myths dispelled. Afterward, I will take them out and teach about celestial navigation. I think it will be fun. Great article!

He showed that even unused needles are often magnetised. To show that usage made a difference, you'd need to show they weren't magnetised to start with.

They may have become magnetised by stray fields in the factory etc. I suspect that they can also pick up the Earth's magnetic field eventually, eg in storage.

The more open places that have obvious landmarks are easy.

The troublesome ones are the ones without much in the way of landmark, like wide open desert or prairie, or in heavy forests.

I've always thought taking an orienteering class would be a good thing, but never have.

Sue

There can also be a problem with knowing which end is north. Get it wrong and the compass can send you in the opposite direction to where you want to go. The time you need a compass most is when you can't calibrate it from landmarks or the stars etc.

If you use a battery and coil, then it is determined by the polarity of the battery and the handedness of the coiling, but I wouldn't be able to remember the theory with enough confidence to rely on the direction.

If you create the compass by stroking the needle with another magnet, then you need to know which end is north of your existing magnet, which if it's, eg the headphone magnet from the example he gives, you probably won't know. And then it makes a difference which direction you stroke in.

If you are able to use the Earth's magnetic field to create a compass, then you need to know which way is north in that, too.

If you carry a sewing kit, then it's a good idea to magnetise the needles in advance, and you should probably make sure you make the pointy end north and remember that you've done it.

Use the Maxwell's screw rule. Very simple:



If a right-handed screw is turned so that it moves forward in the same direction as the current (from + to -), its direction of rotation will give the direction of the magnetic field (North end).

So if making a compass with a battery, a needle and a coil of insulated wire and you want the sharp pointy end of the needle to point north, then from this diagram;



you would put the sharp pointy end of the needle, pointing in the direction of the coil attached to the positive terminal on the battery.

Just checked my EDC flashlight magnet polarity and the makeshift compass performance:



A very flat neodymium magnet from an old HDD is epoxied to the back of the Photon REX (to magnetically mount it anywhere under the car hood, inside a computer case, and to other magnets sewed in my vest, hat, cap, gloves, etc.). It's orienting the On switch to the north in 3 seconds! And very reliably!

I am loving this thread!

-Blast

Looks like the middle drawing from the article graphic is incorrect then as the battery polarities are the wrong way around.

Yep. I've told you...

For me, knowing Maxwell's Right-Hand Rule doesn't help much. It may seem superficially simple because there are only two possible answers. It's hard because there are so many binary elements that can potentially be flipped:

• Wire coiled clockwise or anti-clockwise?
• Clockwise when looking from above, or clockwise when looking from below?
• Current flowing top to bottom or bottom to top?
• Are we talking conventional current flow (ie, positive to negative) or actual electron flow (the opposite)?
• Is the north end the end that seeks north, or the end which has the same polarity as the north pole?
• Left or right-handed screw (or hand, in some accounts)? (Maxwell has both kinds of rule, one for generators and one for motors.)
• Whether the needle picks up the same polarity as the coil, or the opposite polarity?

Knowing a bit more about the subject arguably makes it harder to remember. The difficulty is forgetting the possible accounts/diagrams which are wrong. I think I now know the answer, but I'll probably have forgotten it within a week, because it is all just too arbitrary to keep in my mind. (And further elucidation probably won't help and isn't requested.)

Of those three figures, I think (1) is correct and (3) is wrong. (In (2) I find it hard to tell whether the coil is clockwise or anti-clockwise.) It's interesting that he started with some correct physics and then got it wrong in the construction. It shows how hard it can be to keep track.

A maxim about 3D rendering programs seems relevant here: all correct renderers contain an even number of polarity errors.

Its only schoolboy physics, so it is not really that difficult to get right.

As long as you remember a few conventions.

Rule 1) - Current flows from the positive to the negative battery terminal.

Rule 2) - Magnetic flux lines flow from North to South.



This diagram is useful to remember as is shows a sectional diagram of a magnetic coil. Each circle with a dot in the centre shows current coming towards you out of the diagram and each circle with a cross shows current going away into the diagram. This is just a simplified interpretation of Maxwell's right hand rule.

The magnetic flux lines now indicate the magnetic south polarity is on the left hand side and the magnetic north polarity is on the right hand side i.e. as above in Rule 2.

Now that the north south polarity of the coil has been established from first principles, all that is required now is to determine which direction the sharp pointy end of the needle ends up. Will it be at the North or the South end of the coil.

This is pretty simple; for the sharp pointy end of the needle to point north in the earths magnetic field then the sharp pointy end of the needle has to be magnetised as a south pole. So therefore the sharp pointy end needs to pointing to the south pole of the coil i.e. the left hand side of the above diagram.

Of course if folks cannot tell their right hand from the left hand (you'll be surprised how many youngsters can't) then knowing the above information won't make much difference.

It is complicated, indeed. You've made a mistake too. The North Pole (geographic) of the Earth is actually the South pole of the Earth magnet (that's why the North arrow of the compass is attracted to that direction along the magnetic lines). So, the pointy end of a needle must go to the right on your image.



The problem with the screw rule is that people don't understand the whole picture - how the magnetic field line in particular point of space is forming a closed loop.

Anyhow, it seems to me that if a person is Okay with the simple logic and knows the Maxwell's rule, he/she will figure out what to do with all of that stuff eventually

Looking over these last four posts, I am really glad I can find the North Star reliably.....

It's not a very big advantage in the woods. I'm doing amateur astronomy for the past 30 years. The moving star map is naturally imprinted in my brain. And I can reliably identify almost any visible star by just a handful of nearby stars visible through the very small openings in tree tops. So, I can tell the North direction using any visible stars. However I've realized that it works well only for the northern hemisphere, preferably at +55 latitude, and solely because of 20 years of watching the sky from that old home place. IOW, the other methods are still important to know.

Has anyone seen the film 2012 yet? Lets hope we can keep the pointy end of the needle to the right of the image after Mayan calendar begins a new cycle in 2012 if we still want the pointy end of the needle to point the geographical North pole. Well not exactly the geographical North pole but will instead point to 79.74N, 71.78 W, which is the north geomagnetic pole (actually the geomagnetic south pole)





If only the geomagnetic poles and geographic poles were actually were in the same place and the geomagnetic poles didn't constantly wander around!!

As long as your are on one of the contours marked 0 declination and have followed the above last five posts then you should be able to get your magnetised needle (sharp pointy end) to reliably point to the Geographical North Pole.