Date: Thu, 18 Nov 2004 12:43:20 -0800

Author: "John Welch"

Subject: compass flipping

Post:

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Here's a puzzle that I am having a hard time with-
I have a bunch of cheap compasses in a box on a shelf with lots of =
magnetic demos, including magnets.
Some of the compasses have the red side of the needle pointing north, =
and the others have the red side pointing south. I just figured that =
this was because they were cheap and the manufacturer didn't pay =
attention. So I labeled them according to their orientation in order to =
have two consistent sets. Now a few weeks later, many of the labels are =
wrong, so some compasses must have flipped. What I can't figure out is, =
if a compass is free to orient itself along whatever magnetic field it =
is in (in 2 dimensions at least), why would its magnetic orientation =
reverse?
-John
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Here's a puzzle that I am having a hard =
time=20
with-

I have a bunch of cheap compasses in a =
box on a=20
shelf with lots of magnetic demos, including magnets.

Some of the compasses have the red =
side of the=20
needle pointing north, and the others have the red side pointing south. =
I just=20
figured that this was because they were cheap and the manufacturer=20
didn't pay attention. So I labeled them according to their =
orientation in=20
order to have two consistent sets. Now a few weeks later, many of the =
labels are=20
wrong, so some compasses must have flipped. What I can't figure out is, =
if a=20
compass is free to orient itself along whatever magnetic field it is in =
(in 2=20
dimensions at least), why would its magnetic orientation =
reverse?

-John


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From dwilley+@pitt.edu Thu Nov 18 16:48:53 2004

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