List -- we don't normally do wrist watch or pendulum topics here on time-nuts.
There are many publications [1] and forums [2] for that
Iovane -- but, here's a quick answer:
> This puzzled me since yesterday as I discovered how the suspension of
> pendulum clocks is made, that is a springy plate.
> I thought that:
> -the suspension point (i.e. the point the pendulum moves about) cannot be
> considered fixed,
> -following the above, the lenght of the pendulum varies during a swing,
> -the spring contributes to the oscillation (it cumulates and releases
> energy), i.e. not only gravity at work..
> Ok that we can neglect the above yet having an extremely good approximation,
> but is it conceptually right?
> Thanks for the answers.
When you get to 0.1% or ppm or ppb levels, there is a huge difference between
pendulum motion as described in physics textbooks vs. how real or precision
pendulum clocks operate.
Correct, it's not all gravity; the spring suspension itself has some effect on
the motion of the pendulum. If this is a problem then you make design decisions
about spring length, width, thickness, taper, or what metal to use. Or make the
bob heavier, or choose a different operating amplitude. Or skip the spring
entirely and use agate or diamond pivot suspension. All of this can be worked
out with math or with experimentation.
Correct, the effective length of a pendulum may vary during the swing. This is
due to the geometry of the suspension, flexure in the rod, and changes in
buoyancy. And even if the length were constant, the pendulum is still not
isochronous, due to "circular error". Hence the preoccupation with amplitude
stability as well as length stability.
In general you should not neglect anything until you have modeled or measured
it. Also don't confuse accuracy with stability. A pendulum could swing in a
"figure 8" for all I care, but as long as it does so consistently it can be a
good timekeeper. It's possible that some of the effects you describe affect
accuracy more than stability.
Given your curiosity about pendulum clocks, I strongly suggest you subscribe to
HSN and order the digital archive. These topics are covered in extreme detail
there. You will be amazed.
/tvb
[1] Some pendulum clock resources:
AH (Antiquarian Horology), www.ahsoc.org
HJ (Horological Journal), British Horological Institute,
bhi.co.uk/horological-journal
NAWCC (National Association of Watch & Clock Collectors), www.nawcc.org
HSN (Horological Science Newsletter), NAWCC chapter 161, www.hsn161.com
[2] There are also many clock and pendulum web sites, web forums, and mailing
lists. Contact me off-list.
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