# The Naked Scientists Forum

### Author Topic: If I rub the end of a needle on a magnet what polarity is it ?  (Read 5075 times)

#### neilep

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##### If I rub the end of a needle on a magnet what polarity is it ?
« on: 28/09/2008 19:14:45 »
Dearest All,

See this needle ?

nice eh ?...as far as needles go..it's a prime example of sewing joyness !!

Say I rubbed just the tip of my needle on a magnet !..what polarity would the end of the needle have ?...if I rubbed it on the north pole would it be north ?..and vice versa for south ?

If I rubbed the whole length of the needle along the one end of the magnet ..then what happens ?...would the needle generate both poles ?

Let me know will ewe !

Hugs

Neil
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#### blakestyger

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##### If I rub the end of a needle on a magnet what polarity is it ?
« Reply #1 on: 28/09/2008 19:24:24 »
I think that if your needle had polarity at one end it would have to have the opposite pole at the other - or else there would be no polarity.

Also, although needles were invented for sewing I bet they are used far more for other things; just as chisels can be used for levers, screwdrivers and opening paint tins etc....
« Last Edit: 28/09/2008 19:29:21 by blakestyger »

#### petrovitch

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##### If I rub the end of a needle on a magnet what polarity is it ?
« Reply #2 on: 28/09/2008 19:48:47 »
You would have two magnetic poles and both poles have equal magnetic strength. The polarity could be changed in the needle by reversing the exposure to the magnet for an extended period of time.  For example, drop the needle on the magnet.  Turn it 180 degrees and tape it to the magnet.  The polarity of the needle will change given enough time since the needle has no source of magnetic charge itself.  It is serving only a a temporary bank of energy.     There is a time-reversal degeneracy of the magnetic fields in the needle whereby the needle will lose it's relative strength over time.  Sudden reversal, as stated above, requires much more magnetic energy in the opposite direction to flip the polarity in the needle.  This process is common in computer chips where the magnetic charge is changed to represent different binary states.

Even the polarity of the poles on the earth change.     It is suspected that when this change happens it happens suddenly.  One possible explanation for this is that the core of the earth spins faster and in at a different pitch in relation to the earth's surface.  For some reason the core wabbles until it finally flips and the polarity of the poles on the surface suddenly flip.

Here is a clipping from newbielink:http://science.nasa.gov/headlines/y2001/ast15feb_1.htm [nonactive] entitled The Sun Does a Flip detailing this fact:  Consecutive reversals are spaced 5 thousand years to 50 million years apart. The last reversal happened 740,000 years ago. Some researchers think our planet is overdue for another one, but nobody knows exactly when the next reversal might occur.

newbielink:http://www.geomag.bgs.ac.uk/reversals.html [nonactive] entitled In the News: Magnetic Flip says: The Earth has a magnetic field, as can be seen by using a magnetic compass. It is mainly generated in the very hot molten core of the planet and has probably existed throughout most of the Earth's lifetime. The magnetic field is largely that of a dipole, by which we mean that it has one North pole and one South pole. At these places, a compass needle will point straight down, or up, respectively. It is often described as being similar in nature to the field of a bar (e.g. fridge) magnet. However there is much small-scale variation in the Earth's field, which is quite different from that of a bar magnet. In any event, we can say that there are currently two poles observed on the surface of the Earth, one in the Northern hemisphere and one in the Southern hemisphere.
By magnetic reversal, or 'flip', we mean the process by which the North pole is transformed into a South pole and the South pole becomes a North pole. Interestingly, the magnetic field may sometimes only undergo an 'excursion', rather than a reversal. Here, it suffers a large decrease in its overall strength, that is, the force that moves the compass needle. During an excursion the field does not reverse, but later regenerates itself with the same polarity, that is, North remains North and South remains South.  As a matter of geological record, the Earth's magnetic field has undergone numerous reversals of polarity. We can see this in the magnetic patterns found in volcanic rocks, especially those recovered from the ocean floors. In the last 10 million years, there have been, on average, 4 or 5 reversals per million years. At other times in Earth's history, for example during the Cretaceous era, there have been much longer periods when no reversals occurred. Reversals are not predictable and are certainly not periodic in nature. Hence we can only speak about the average reversal interval.

« Last Edit: 28/09/2008 20:15:46 by petrovitch »

#### lyner

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##### If I rub the end of a needle on a magnet what polarity is it ?
« Reply #3 on: 28/09/2008 20:03:20 »
Your poles wouldn't neccessarily have the same 'strength' (meaning the density if field lines or flux) remember, all the 'poles' are is where most of the lines go in and come out of the magnet. You could have one small strong pole and one large weak pole.

#### LeeE

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##### If I rub the end of a needle on a magnet what polarity is it ?
« Reply #4 on: 28/09/2008 21:59:13 »
Sorry to raise the issue, but that needle is clearly broken.

How can you expect to make sense out of something that's broken?

#### The Naked Scientists Forum

##### If I rub the end of a needle on a magnet what polarity is it ?
« Reply #4 on: 28/09/2008 21:59:13 »