vdg pinwheel (was Re: electrostatic motor)

[Chuck Britton <cvbritton@TELOCITY.COM>]

               from the Tap-L list
Hi Wolfgang,

A grad student and I were puzzling over this earlier in the year.  We
developed a new demo that might help to answer your question, which was to
stick a pointed object on the vdg surface, and aim this at a piece of
paper suspended from a string.  The paper is pushed away from the point
(showing an effect opposite to that for the paper near a smooth surface,
which is attracted by induction). We thought that this was a clearer demo
of the electric wind than the candle, because the question then arised as
to whether combustion products (dust, ions, etc) were required for the
effect (answer: no).  And actually, since a candle flame between parallel
plate electrodes also bends, even though there are no sharp pointed
electrodes and even though the electric field is fairly uniform, there
is some kind of additional effect, due presumably to the combustion
in the flame, which is separate from the effect of sharp charged edges.

Also, following a lead from Bill Beaty's vdg stuff, we aimed the point (a
nail taped to the vdg surface) at an electroscope, and watched the
electroscope charge.  We could charge the electroscope even if the
electroscope was 2 (or more) meters away, as long as the electroscope case
was grounded.  In fact, you can stick your hand in the path and
feel the stream of charged particles.

We looked in the literature, a vast literature on the electric
wind, and found the question of "what is blowing?" was a big
question for many years.

Our conclusion was that the strong and *non-uniform* electric field near
the sharply curved conductive surface caused the air molecules to break
apart;  by momentum conservation & the 3rd law, this caused the vdg
pinwheel to whirl (regardless of polarity), with a flow of charged
particles in the opposite direction.  The charged particles, in
this model, are not originating from the point, but from the "explosion"
in the air when the air molecules break down.

Steve W.


On Thu, 18 May 2000, Wolfgang Rueckner wrote:

>  Date: Thu, 18 May 2000 14:03:02 -0400
>  From: Wolfgang Rueckner <rueckner@fas.harvard.edu>
>  Reply-To: tap-l@listproc.appstate.edu
>  To: tap-l@listproc.appstate.edu
>  Subject: Re: electrostatic motor
>
>
>  >Here's a trio of observations.
>  >
>  >People who have used or built room air ionizers are familiar with the fact
>  >that either negative or positive ions can be generated by these devices and
>  >measured objectively.
>  >So the puzzle is essentially a non-puzzle.
>
>  Having just done the new experiment (positive flame is repelled by wire
>  regardless of the wire's polarity), the puzzle of why the whirlygig doesn't
>  change direction is answered. But now we have a new puzzle (question).  Why
>  is the flame always repelled?  Wolfgang


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Steven K. Wonnell
Physics and Astronomy Department        E-Mail:  wonnell@pha.jhu.edu
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Chuck Britton                                   Education is what is left when
britton@academic.ncssm.edu                      you have forgotten everything
North Carolina School of Science & Math         you learned in school.
(919) 286-3366  x224                            Albert Einstein,        1936