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From: rah@netcom.com (Richard Hyde)
Subject: Re: compass errors
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Date: Sun, 25 Oct 1998 16:46:41 GMT
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Mike Regish (mregish@map.com) wrote:
: OK, but what is the magnetic equivalent of the weight in your thought
: experiment. The magnet should be balanced or it won't work so as far as I
: can figure inertia is not a factor here.

: >Thought experiment:  Take a 10 ft. 2x4 and place a 2Kg weight on one
: >end.  Now hold it in the middle and start to run with it.  What happens?
: >
: >The end with the weight swings backwards.  Towards you.

I only intended to illustrate the effects of inertia on a central
pivoting, unequally weighted bar.  You are correct in noticing that
my "thought experiment" did not include an analog for the magnetic
force affecting the compass.

That's a tough one.  OK, how about this?  You accept that the compass 
needle aligns itself with the magnetic field lines of the earth, yes?
Thus, in the Northern hemisphere, the needle "dips" to the north, i.e.
points towards the ground.

Take my example above and let the 2x4 pivot up and down as well as
right and left.  The weighted end will be pulled to the ground. 

Attach a horizontal sail to the non weighted end of the 2x4 and
set up a large fan to blow down on it.  This downward blowing
wind exerts a downward force on the sail and simulates the downward
pointing component of the earth's magnetic field.

With the right size weight, sail, and fan, you will have a balanced
system that will still behave as I originally described.  Run forward
and the weight will swing towards you, slow down and the wright will move
away from  you.  

The force causing the "needle" to dip (magnetic or fan) does
not have mass.

I'm afraid this explanation is becoming more complex than just imagining
a regular compass needle weighted on the South end to eliminate dip :-)

Cheers,

Rick

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