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Re: Malcolm's ruler machine
Hi Terry,
I love your machine there is nothing like seeing an analogy to help build a
mental model of something. If you have strobe light you can use it to see
the motion by setting it a bit faster or slower than the frequency of you
wire.
Try this conundrum the velocity of sound in your wire is probaly more than a
1000m/s.
I suggest you next try one of those spring toys that walk down stairs.
Problem is its own weight stretches it too much if you hang it vertically.
You could try horizontally suspending it from several threads along the
length. This may even exhibit dispersion. What about a cylinder of jelly.
You voltage profiles are intriguing. What is the spatial resolution of your
probe.
Regards Bob
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Thursday, May 25, 2000 10:55 PM
Subject: Malcolm's ruler machine
>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>Hi All,
>
>I have built sort of a fun toy to study secondary resonance. Going off
>Malcolm's analogy of a bent ruler model for secondary oscillation, I built
>a simple device.
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/Mach.jpg
>
>It is simply a wooden base with a spring steel wire pressed into a hole. A
>"woofer" speaker is connected to the base of the wire by a rubber band and
>some small powerful magnets to couple the speaker cone to the base of the
>wire. The wire is 30.0 inches long and weighs 11.7 grams. The wires
>natural frequency is 1.81 Hz.
>
>The speaker is driven by a DC-50kHz amplifier from a low frequency
>oscillator with a scope attached to measure frequency:
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/drive.jpg
>
>The first harmonic occurs at 1.81Hz where the wire swings with great
>amplitude. Decreasing the amplitude did not change the resonant frequency:
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/1st.jpg
>
>The third harmonic occurs at 12.11Hz with far less amplitude. The nodal
>point is 23.5 inches from the base:
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/3rd.jpg
>
>The fifth harmonic is at 34.13Hz with nodes at 15.25 and 26.0 inches:
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/5th.jpg
>
>The seventh harmonic is at 66.23 Hz with nodes at 10.75, 19.25, 27.0
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/7th.jpg
>
>it is interesting to compare this to actual secondary coil measurements at:
>
>http://users.better-dot-org/tfritz/VoltDistBare.jpg
>
>Is is also interesting to note the similarity of the wire bending profile
>to the graph profile of the measured results:
>
>http://users.better-dot-org/tfritz/site/misc/MalRulMa/Wire.jpg
>
>It is interesting to also note the measured profile is concave rather than
>convex as would be expected in a 1/4 wave sine function as shown in the
>comparison graph here:
>
>http://users.better-dot-org/tfritz/DistGraph.jpg
>
>I don't know what all this means or anything but I wanted to pass this
>information I had on for everyone's enjoyment... Maybe it will all mean
>something to someone. I have been so busy getting the thing working that I
>have not thought much about the implications...
>
>For reference, there are many web sites with spring, mass, and oscillation
>information such as:
>
>http://www.futuresouth-dot-com/~mhenders/physics/Simple_Harmonic_Motion.htm
>
>http://www.cs.wright.edu/~fdgarber/199/Spring_Mass_3/
>
>I will try adding weight at the top (like a terminal load) and such in the
>future. I have to start working on the cap bulk buy first ;-))
>
>Cheers,
>
> Terry
>
>