This is an interesting point that Randall makes.  I suppose if there 
is always some movement due to microseisms, then the static friction 
will not come into play...  but maybe not .... at the end of each 
swing it may be a factor anyway, causing the response to be nonlinear.

I wonder if there are also complexities of this sort in other types 
of hinge that involve flexure of a material?

John

>Date: Thu, 25 Oct 2007 08:59:01 -0400
>From: Randall Peters 
>It's a neat piece , Meredith; however, I see a serious problem with 
>bearing friction when it comes to use in
>a seismometer.  Rolling friction is really complex, as evidenced by 
>the paper I wrote at
>http://arxiv.org/abs/physics/0506143
>   My expectation is that you will find challenges due to `stiction' 
> since the decay of your system (independent
>of damping that you supply to the instrument by design) is more in 
>the category of Coulomb friction than
>forms that result in exponential decay.  As is well known for 
>Coulomb friction, the static coefficient is greater than the kinetic 
>coefficient.  Consequently, you would probably need to provide some 
>way to dither your instrument to have much in the way of sensitivity.
>
>Randall Peters


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