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Re: rolling nail puzzle



On 03/25/2003 06:11 AM, Mark Sylvester wrote:
>
To his surprise, the nail rolled the other way!

I predict if you look closely enough, the nail
will roll in the "normal" outbound direction
for a short (ms) time before turning around
and rolling inbound.

I further predict that the turnaround will be
more observable if you use something like a tin
can. (As usual, "tin" can means tin-plated steel.)

> In fact, he says the nail
always moves towards the battery, regardless of direction of current.

Fundamental symmetry arguments ensure that whatever
happens will be independent of the direction of
current.
http://www.monmouth.com/~jsd/physics/pierre-puzzle.htm

> I have a vague hypothesis that it's something to do with rolling
behaviour
- that the current in the nail is concentrated along the bottom - perhaps
because of lower conductivity of iron - and this results in a pull to the
right at the bottom causing rolling to the left:

Not a chance.

===========

Hints:
-- Energy of diamagnetic object in a field.
-- Energy of ferromagnetic object in a field.
-- Principle of virtual work.