[amsat-bb] Re: Earths Magnetic Field strength

Robert Bruninga bruninga at usna.edu
Wed Feb 21 06:34:44 PST 2007

> 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

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.

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