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#189884 - 12/04/09 07:49 AM Re: Awesome article about improvising a compass [Re: GarlyDog]
Alex Offline
Old Hand

Registered: 03/01/07
Posts: 1034
Loc: -
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).



Edited by Alex (12/04/09 07:52 AM)

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#189897 - 12/04/09 02:40 PM Re: Awesome article about improvising a compass [Re: Blast]
Glock-A-Roo Offline
Old Hand

Registered: 04/16/03
Posts: 1076
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...".

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#189910 - 12/04/09 04:34 PM Re: Awesome article about improvising a compass [Re: Glock-A-Roo]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
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

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#189921 - 12/04/09 05:34 PM Re: Awesome article about improvising a compass [Re: Susan]
Alex Offline
Old Hand

Registered: 03/01/07
Posts: 1034
Loc: -
Susan, the better way is needle on a thin string. However it's still better to use landmarks including sun, wind, and clouds movement.

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#189922 - 12/04/09 05:40 PM Re: Awesome article about improvising a compass [Re: Alex]
hikermor Offline
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7191
Loc: southern Cal
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.
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#189980 - 12/05/09 07:41 AM Re: Awesome article about improvising a compass [Re: hikermor]
MostlyHarmless Offline
Old Hand

Registered: 06/03/09
Posts: 982
Loc: Norway
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.


Edited by MostlyHarmless (12/05/09 09:23 AM)

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#189993 - 12/05/09 01:47 PM Re: Awesome article about improvising a compass [Re: MostlyHarmless]
gonewiththewind Offline
Veteran

Registered: 10/14/08
Posts: 1517
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!

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#189999 - 12/05/09 04:21 PM Re: Awesome article about improvising a compass [Re: Alex]
Brangdon Offline
Veteran

Registered: 12/12/04
Posts: 1201
Loc: Nottingham, UK
Originally Posted By: Alex
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.
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.
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#190026 - 12/06/09 12:23 AM Re: Awesome article about improvising a compass [Re: MostlyHarmless]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
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

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#190053 - 12/06/09 11:16 AM Re: Awesome article about improvising a compass [Re: Susan]
Brangdon Offline
Veteran

Registered: 12/12/04
Posts: 1201
Loc: Nottingham, UK
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.
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