## PSN-L Email List Message

Subject: Re: Fw: Long Period Pendulum
From: ian ian@...........
Date: Mon, 25 Feb 2008 13:33:35 +0000

```Hi,

I didn't get very far, due to lack of time.  I used a threaded rod which
screws through a threaded hole in the body of the pivot.  The rod was
only 5mm in diameter and wasn't very strong, so when the pendulum was
heading towards each extreme it would bend and the pendulum's motion was
very complicated.  My next step would be to try it with a larger
diameter rod, one day...

With the limitations mentioned above, I only got 5 seconds out of it and
it wasn't stable enough to behave in the way it should, like resting at
2 o'clock.  I think the main benefit of an asymmetrical arrangement will
be that you get more movement at the bottom end (for a given length)
which may make seismic excitations of the pendulum (as a tiltmeter)
measurable!

Good luck!

Ian

tchannel1@............ wrote:
> Hi Ian,  That was my next test,   I want to try this just as you
> indicated. What did you find?  Did it change the maximum period possible?
> Did you find that your experiments, where the pendulum wanted to favor
> the 2:  o'clock vs vertical, as you approached longer periods?
> Thanks, Ted
>
> ----- Original Message ----- From: "ian"
> To:
> Sent: Monday, February 25, 2008 12:49 AM
> Subject: Re: Fw: Long Period Pendulum
>
>
>> I was playing with something like this but with the pivot near the
>> top end of the rod.  The top weight was much bigger than the lower
>> weight in proportion to the lengths of the sections above and below
>> the pivot.  That way, you'll get more movement at the bottom end of
>> the long section than you are currently getting with your symmetrical
>> arrangement.  Balancing is a little more tricky because of the
>> asymmetry.
>>
>> Given that this is probably working as a tilt meter, getting a long
>> period may not be too important.
>>
>> Ian
>>
>>
>> Brett Nordgren wrote:
>>> Geoff,
>>>
>>> I believe that the only problem is that the amplitude of tilt
>>> oscillations from quakes would be rather small, and they are only
>>> associated with some of the phases.  But it should definitely be
>>> worth a try.
>>>
>>> Regards,
>>> Brett
>>>
>>> At 01:21 PM 2/24/2008 -0700, you wrote:
>>>> WHAT WOULD be wrong with building a
>>>> device that is fixed in a level
>>>> fashion and measure only tilt since
>>>> distortions stress and strain in the earth
>>>> will manifest itself as a tilt ?
>>>>
>>>> It may be easier and cheaper to do this ?
>>>>
>>>> regards;
>>>> geoff
>>>
>>>
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