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Bill Morris (engineer@clear.net.nz) wrote, about adding fine-adjustment
weights to a precise pendulum clock-


"The regulating weight is usually half to two thirds of the way up the
pendulum. It has maximum effect at the half-way point, but it looks better a
little higher. Adding weights to the top of the pendulum bob does work, but
they have to be heavier. On the home-made regulator clock whose picture I
include as an attachment, I use increments of 100 milligrams and can achieve
a rate of two or three seconds a month, but as the brass-compensated Invar
pendulum rod is not (yet) correctly compensated, the rate changes with the
season."

==========================

It isn't obvious to me whether adding an extra "regulating weight" to the
top of the bob would speed the clock up or slow it down. There will be two
effects, which work in opposite directions.

1. If we can consider the rod as of negligible weight and inertia, compared
with the bob, then adding that exrea bit at the top will raise the centroid
of the bob and therefore effectively shorten the length and speed the clock
up.
2. On the other hand, if the rod is not weightless, then adding extra weight
to the bob, at its centroid, would by increasing the weight of the bob,
reduce by a small proportion the relative effect of the rod, thus slowing
the pendulum down.

So in the real situation, with a rod that isn't weightless, and an extra
adjusting-weight that's above the centre of the bob, which of those effects
wins?

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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