PSN-L Email List Message

Subject: Re: pendulum that generated 'rattle in seattle'
From: tchannel1@............
Date: Sun, 11 Nov 2007 20:05:22 -0700

Geoff,  Please where are you located?

----- Original Message ----- 
From: "Geoff" 
Sent: Sunday, November 11, 2007 4:47 PM
Subject: Re: pendulum that generated 'rattle in seattle'

> 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.
> Regards;
> geoff
> ----- Original Message ----- 
> From: "Randall Peters" 
> To: 
> 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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