# Re: Earths Magnetic Field strength

• Subject: [amsat-bb] Re: Earths Magnetic Field strength
• From: "lu7abf" <lu7abf@xxxxxxxxxxxx>
• Date: Wed, 21 Feb 2007 13:00:17 -0300

```If the separation between poles of a small magnet defines strength of force, then a small separation as in a magnetic compass needle only 1 inch long placed at equator, over 6000 miles from poles will not move. Instead it does.

Also much smaller magnetic dipoles even molecular inside a melted ferrous material does orient and keep their mood if material crystallize.

I think it is a matter of poles orientation i.e. on small needle, north pole is opposite to south, so it does not exert force in the same direction of the south pole, but opposite. (It's difficult to explain without using a sketch, and in a not my mother language, excuse me)

Regards to everybody and thanks for lending some brain cells to the idea of trying control bird's height.

73, Pedro Converso
lu7abf@amsat.org.ar
www.amsat.org.ar

Robert Bruninga wrote:

>> I moved a handheld compass towards a heavy... speaker magnet.
>> When the compass was a few inches away from the magnet,
>> it changed direction from North to the direction of the magnet.
>
>As someone else pointed out earlier, that is because of the
>gradient or difference in "force" on one end versus the other.
>One end of the compass was an inch or so closer to one pole of
>the magnet than the other end.
>
>But in space, the pole of your spacecraft magnet that you are
>trying to repel, is only one foot closer to the Earths pole,
>than the other pole which is attracted.  So the difference in
>distance of the force that is pulling to the one that is pushing
>is only 1 foot out of say 21,120,000 feet to the Earth's pole.
>Hence the net force difference is a 21 millionth SQUARED or
>.00000000000004 of the force that you observed on the compass.
>
>Or something like that.
>Bob
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