Hi Randall,
Thanks for the patience, humor, speculation and encouragement. I've re-read the below quite afew times and alas,
it just simply doesn't register with me, as a "why; is it oscillating longer than a standard S-G?". Mind you, that
could very well be "it", in the boom itself; I literally just don't know myself.
I've even tried 2 (different) small carbide flats (attached to the boom), which oscillate on 2 same size (but different)
fixed/glued to the frame ruby balls. The time duration remained within one minute as the opposite. This "oscillating
flats on fixed balls", was a curiosity test directly relating to Chris Chapmans new flat end boom pivot oscillating on a
mast fixed ball on a horizontal Lehman; which seems to greatly offer more overall stability, ease of use, and seemingly even
a possible longer natural period. I've put that curiosity flip/flop pivot test text (no pic's yet) on the same page today, but it was
done in July.
Simple strictly vertical gravity pendulums using similar carbide flats and exact same size ruby balls consistently have fallen
shorter in time duration oscillations by 1/2 to 1 hour less. In short; the offset pivot seems to freely oscillate ~ > 14% or more longer
than a traditional simple gravity pendulum pivot. Outside of pivot/s and air resistance, there is no (eddy current) dampening
on any of these setups.
On another web page, I've listed a variety of S-G pivots tests. This offset pivot is listed as 1. & 2. Number 3, a traditional S-G,
has actually seen more tests (switched carbide flats) than shown, or listed; but they ranged from 2 hours 40 minutes up to 2 hours
55 minutes. The ruby ball remained the same.
In reality, this pivot sure isn't a practical use pivot; unless there is a rapid mechanical way of referencing and insuring pivot placement for
what ever degree offset is "best?"....and even then, it might be too overall complicated for replication.
Of course the eddy current dampening mechanism would also have to be mechanically varible for the different angle and height
changes one might encounter. I also can't see how "measuring the damping as a function of the amount of offset" could possibly
enter into the overall picture, or have any significant value....I would think it would remain the same...but then, I'am often wrong....
Take care, Meredith Lamb
On Thu, Aug 14, 2008 at 10:08 AM, Randall Peters
<PETERS_RD@..........> wrote:
Meredith,
I am glad that you discovered the absence of vertical sensitivity
in your system. Otherwise I would have to revisit some foundational
physics!
About the offset pivot--perhaps you have discovered something
significant that nobody seems to have noticed. Internal friction in the
rod holding the lower mass is bound to be of greater importance than
most people would expect. Perhaps because of the bending stresses
associated with the offset pivot, there could be some 'locking-up' of
dislocations in the rod and thus a reduction in the damping that derives
from this contributor. One would want to be sure that your improvement
is not simply due to the better properties of the ruby balls, compared
to what you were previously using?. Ruby differs from pure aluminum
oxide crystals only in the nature of the color centers due to impurities
(chromium for ruby, titanium for sapphire; although usually the pure
material without substitutional impurities is also called simply
sapphire).
Can you readily modify the system to measure the damping as a
function of the amount of offset? It would be an interesting study
with potentially significant consequences to seismology.
Randall