Re: navigation riddle

[Craig Lucanus <lucanus@IINET.NET.AU>]

OK John, deal me in.

 Point A is the north magnetic pole. The compass at this point would gyrate
causing you to speculate as to whether it was the north or south pole at
which you were situated. Walk a straight mile in any direction. At B the
compass would point in the direction from whence you came, establishing that
direction as due north and allowing you to establish the easterly direction.
East 1 mile (or kilometre or chain or anything) your compass would point to
the point you started from, the north magnetic pole.

Alternatively, you could use your compass  as a declinometer by holding it
vetically when you suspected you were at a magnetic pole. The needle would
point straight down.

How about that?

Yours sincerely
Craig Lucanus
----- Original Message -----
From: "John Denker" <jsd@AV8N.COM>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Thursday, August 12, 2004 7:03 PM
Subject: navigation riddle


> Since phys-l has been somewhat listless lately, here
> is a riddle:
>
> Dr. Livingstone starts out at a place which we call
> Point A.  He then undertakes a journey consisting
> of three legs:
>   -- he travels precisely southward for one mile;
>   -- then he turns and travels precisely eastward
>      for one mile;
>   -- then he turns and travels precisely northward
>      for one mile.
> He discovers that as a result of this journey, he
> has returned to Point A.
>
> Note: He travels by airship, at an appropriate constant
> altitude, so you don't need to worry about obstructions
> or other nonidealities.
>
> The questions are:
>
> 1) Where is Point A?
> 2) Are you sure?  How do you know?
>
> ===========
>
> Usual ground-rules:  The right answer depends on
> understanding the physics of the situation.  This may
> require some outside-the-box thinking.  Everything
> I've said is intended to be true and helpful.  I expect
> a strong consensus as to the correctness of the answer.