Re: Fridge magnet physics Was: Air Hoses - what to do ---

David Smith

Fridge magnets are polarized in alternating strips so as to result in a
strong field on one side and a minimal field on the other. You can
demonstrate the striped nature by placing two magnets witht he fridge
(non-message) side face-to-face (they will attract), then slide one across
the other. In one combination of directions, you will feel a stuttering
slip, any other combination of directions will slip smoothly. The
stuttering happens when both sets of strips are perpendicular to the
movement direction and parallel to each other. The alternating attraction
and repulsion of pairs of like and unlike strips causes the sensation of
alternating sticking and slipping. I don't know whether Mr. Davis uses this
property intentionally or not but even random punches are likely to have at
least two strips in them and they will attract each other.

Dave Smith

On 10/21/07, Tom Madden <tgmadden@...> wrote:

John Hitzeman wrote:
One of the most remarkable things I've seen is what Dave Davis
has done. He made a little punch in the form of a glad hand and
punches them from thin kitchen magnets. Then he uses the
no-sag thread from Walthers High Tension Tower kits to make
the hose. With the magnet on one end, and the other end of the
hose ACC'd to the angle cock, the hose hangs down at
Denny's prototype angle. But, when the cars are being coupled,
the magnets attract each other and, as if by magic, the
hoses couple by themselves, yielding a prototype appearance
as the train passes by.
Not to be picky, John, over what appears to be a brilliant technique,
but wouldn't there be, at best, a 50:50 chance that the magnets would
repel each other? Those thin magnets are polarized across the faces,
so glad hand-shaped discs punched from them would be as well. If the
discs can be attached to the Walthers thread facing either way, you
get your 50:50 chance. If they can only be attached one way, they
would always repel. Or am I missing something???

Tom Madden

David L. Smith
Da Vinci Science Center
Allentown, PA

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