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Subject: Re: Fw: Long Period Pendulum
From: Brett Nordgren Brett3mr@.............
Date: Mon, 25 Feb 2008 11:23:33 -0500


If you are just wanting to measure tilt (rotational oscillation), as 
Randall Peters has pointed out elsewhere, the natural period doesn't enter 
into the calculation.  Natural period does get involved with a second-order 
effect related to moments generated by an imperfect hinge or by intentional 
damping, but those could likely be reducedd or ignored.  I think, In 
general, for measuring rotational motion you would prefer a pendulum which 
maintains a stable position rather than a less stable long-period setup.


At 01:33 PM 2/25/2008 +0000, you wrote:
>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!


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