ok, I think I understand.

But unlike a pendulum the disc has
mass all around so that momentum exists
at top as well as bottom. If you cut the disc
off the top and sides you now have a thing
much like a pendulum only with an
Axel instead of an end point.

I have often thought you could balance
a mass on a point which would always be level
then simply look at the angular displacement to
derive your signal.
You might somehow use a liquid level
with an opaque liquid and shine a laser light through
the bubble or prism or mirror to a sensor.
Waves produce level points at four times
0, 90, 180, 360 degrees. This way you
look at only surface waves and not up/down motion.
Up and down motion will not produce outputs.

I know there must be really interesting designs out there
that none of us have seen before.

I have often thought of an electron microscope
being used to actually measure nanometers of motion of
some mechanical device like a seismometer.
Producing a very accurate and precise
measurement of motion.

In what I mentioned earlier the mass would be
100% submerged and the liquid would also
be the damper. Your mass would be such
like a cylinder or sphere.
I see no reason  why it should not work
But this is all speculation on my part.
The momentum of the mass should
be the same even with the forces
cancelling each other.
94% of the weight only being
cancelled by fluid bath.
6% supported by the spring
at whatever extension produces 5 seconds
of free period.
Momentum is the key here
and not really the spring length.
So I think 10 inches of extension
should be sufficient if you somehow
subtract 94% of the mass weight.
Leaving only 6% to support by the spring.

If you can show simply with math why this won't
work. Please show me.

You can not use the formula P=2Pi(l/g)^0.5
for this idea but something more like F=MA.
F should be the same in the fluid as in the Air.
Or so it seems to me.
The tiny spring will feel the 100% mass
momentum and not the 6%.
But the damping in the fluid will be much greater
than air.

Does any of this make sense ?

I am no math expert.
As you can tell.

Regards,
geoff








-----Original Message----- 
From: Brett Nordgren 
Sent: Sunday, November 21, 2010 7:09 PM 
To: psnlist@.............. 
Subject: Re: http://www.1goss.com/Arkansas42.jpg 

Hi Geoff,

I'm not sure, but I think the suggested design might suffer from lack 
of sensitivity.  Simply having a long natural period doesn't, by 
itself, necessarily make for a good seismometer.

For example, consider a horizontal design made from a large metal 
disk which has a horizontal axle in a frictionless bearing.  Add a 
weight of a few grams on its rim and the disk will slowly rotate to 
have the weight move towards the bottom.  It will also act as a 
pendulum and will oscillate with a very long period.  But if you go 
through all the math, it turns out that it will have very little 
sensitivity to horizontal ground motions.  Long period alone doesn't 
equal a good seismo.  I think the proposed vertical design is also 
trading sensitivity for long period.

Regards,
Brett

At 01:14 PM 11/21/2010, you wrote:
>
>
>I have been looking at gravity normalized to 1G
>for various periods of a pendulum and come up with
>the following Idea.
>
>Given: 1g and 1sec period (P)
>Find: new values of g for any given period.
>
>g = 1 / P^2
>
>This means if you could float lead in some kind of
>dense fluid which through buoyancy removes
>94% of its weight you might get a 5 second period
>by then suspending the submerged piece of lead
>by a spring extended by what might be
>10 inches or so of extension from zero.
>I have not tried this, possibly one of you know more ?
>What fluid is dense enough to take up the weight
>of lead which is like 11.4 grams/ml
>you need a fluid with a density of like
>11.4 * .94 or 10.72 grams / ml.
>I can find no such fluid, but is there a way
>to create such a fluid of practically any
>density you might need ?
>
>I figure anything which can counter 94% the mass weight
>will give the same result. Not just fluids.
>
>Am I wrong here ?
>
>http://www.1goss.com/Arkansas42.jpg
>
>Comments Please, private or public welcomed.
>
>geoff


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