PSN-L Email List Message

Subject: Re: pendulum that generated 'rattle in seattle'
From: "Geoff" gmvoeth@...........
Date: Sun, 11 Nov 2007 16:47:56 -0700

Wunderbar, Thanks for the enlightenment;

I still would like to know why voltages
get higher near pointed objects
sort of like a point is acting like a
resistor so possibly you could
get a good current moving that at the ends
of a solid tapered piece of copper
or silver or room temp superconductor
might possibly generate decent voltages
without all those loops of fine wire.
Just a thought relating to antennas
I used to play with, you can increase the
impedances by using a gamma match ( smaller
diameter conductor ) or by tapering their ends
at the feed point on the driven element ??

Do you know someone who makes and sells
decent magnet coil sensors possibly according
to my own wishes. I lack the resources to
anything decent myself.

I like that vertical seismometer that looks
similar to a horizontal garden gate type
but none seem to have a sensor arrangement
which i like to see ??

I have looked into custom springs but like
the Century people want $100 + USD
just to make a single spring ( They call it
setup costs ) ??
I guess if people like the spring one get
somekind of gratuity in return from the company ??

Thanks for your replies.
I always like hearing from science peoples
about science stuff.
Here in SandRock Arizona we seem to be in the Stix.


----- Original Message ----- 
From: "Randall Peters" 
Sent: Saturday, November 10, 2007 8:21 AM
Subject: pendulum that generated 'rattle in seattle'

> Geoff,
>     The pendulum responsible for the now-famous picture you and Meredith mention (and give the American Physical Society-hosted 
> sebsite) is not like the dangling pendulum we've been discussing.
>    As you noted, it is a 'toy'-version of the one that I studied (responsible for the aforementioned article on chaos) and which 
> has for years been used to generate beautiful art-pieces.
> A picture of that pendulum which I built (while still at Texas Tech University) and which is here in the Mercer physics department 
> is to be found at
>       Also on this website are some of the myriad traces that have been produced with the pendulum.  Art-folks love these because 
> of their 'life-like' properties--no two exactly the same (quite unlike computer generated patterns).
>   The bowling ball is supported by a pipe on one end, the other end of which is connected to a universal joint (off a toyota 
> pickup if I remember correctly).  Because of this U-joint, the x-y axes
> are coupled, giving rise to a very large number of different patterns during free decay.  The moments of inertia in the
> two axes are adjustable to provide additional control that assists the near infinity of possible results.  In the absence of 
> friction, this instrument would display what's called Hamiltonian chaos.  The sensitive dependence on initial
> conditions (essence of the butterfly effect) means that long term prediction (just like the weather) is
> unpredictable.  There are two capacitive sensors that map the motion of the bowling ball, one in each of the perpendicular axes. 
> The output from the amplified signals is fed to an x-y (analog recorder) that with a ball-point
> pen generates the images on ordinary paper.
>   I have done a lot of chaos research in the last 15 years.  The chaotic pendulum that I designed and which is
> online here at Mercer (when my colleague Matt Marone gets it back operational after our move to the new
> building) is at
> This pendulum can be controlled from anywhere in the world over the internet when operational.  The parameter
> that the user can adjust is the frequency of the drive.  The pendulum's motion is monitored by one of my SDC
> sensors functioning as a velocity detector.  An aluminum disk rotates with the pendulum between rare-earth
> magnets positioned on either side, which are on the end of a bending cantilever.  The output (velocity) is integrated
> with a 'leaky' integrator to give the position.
>    Largely because of my pendulum chaos studies I was asked and wrote an article on " math methods used by physicists to study 
> chaos" for the 10th Ed. of the McGraw Hill Encyclopedia of Science and Technology.  I'm sure that some readers will note the 
> prominence of other authors in the chaos section of the encylopedia (such as the creator of the butterfly effect, Ed Lorenz) and 
> then will say, "but who's this guy, Peters?".
>     You ask, Geoff, 'why use multiple turn coils for the Faraday-law sensor.  The answer is resident
> within the statement of his law (generated, in the minds of most, by the greatest experimentalist who ever
> lived).  Faraday's law states that the voltage generated within the wire (historically called the electromotive force (emf) even 
> though voltage is not a force) is proportional to the number of turns of the coil times the time rate of change of the magnetic 
> flux passing through the coil.  Thus no matter how your amplifier is built (solid state or vacuum tubes) the signal will be 
> greater the larger number of turns you can wind within the constraints of space limitations borne of wire size and increased 
> resistance that
> results when the wire gets too small trying to put more turns into a given place.
>   Randall


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