# OT?...How does gravity vary?

Discussion in 'Electronic Design' started by Roy Hammond, Feb 10, 2007.

1. ### Roy HammondGuest

Pendulum clocks - the usual electronic movement type (battery feedback
pulses solenoid when magnet on pendulum passes by).

My experience with these movements is that they are somewhat delicate: you
have to carefully adjust the clock movement vertically and horizontally
until the pendulum swings reliably.

However after running for several hours, sometimes the pendulum stops.
I think that I've ruled out the battery as the guilty party.
That set me to wondering: does gravity vary? If so, what are its
characteristics? Could gravity changes account for the pendulum stopping?

2. ### Don LancasterGuest

Try a horizontal pendulum.
It would be independent of gravity.

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3. ### Homer J SimpsonGuest

Yes. Sometimes the heavy gravity sits as a layer on top of the light gravity
and holds it down causing a gravity inversion layer.

4. ### GarethGuest

Gravity varies a little bit due to the effects of the sun and moon
(which is why we have tides) but I doubt that this is the reason for

Gravity also decreases with increased altitude, and is slightly
different at different places on the Earth's surface due to different
local geology.

A gravitational force of attraction exists between any objects with
mass, so in theory moving any object would cause a change in the total
gravitational force seen by the pendulum. However, the Earth is very
large and close, so most other things will not cause any detectable change.

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5. ### Paul Hovnanian P.E.Guest

There appears to be an accumulation of the heavy gravity underneath my
bathroom scale.

6. ### Paul Hovnanian P.E.Guest

I don't think variations in gravity are stopping your clock. I have one
that has been running on one AA battery for about 2 years.

The pendulum needs to be aligned not only in the lateral plane (side to
side so that it swings equally to either side of the solenoid
mechanism), it needs to be aligned fore and aft so that the pendulum's
bearing (usually some sort of blade or wedge shape) makes contact with
its rest with minimal friction.

7. ### Homer J SimpsonGuest

And when teenage boys watch porn the reverse seems to happen in their pants!

8. ### Robert BaerGuest

Nope! No observable reason for it to stop other than dirt accumulated
in the bearings due to (too much) oil.
The force of gravity changes with locale; known to be stronger near
large deposits of iron.
Extremely doubtful of local "modulations", and the variations
mentioned above are very small.

9. ### Robert BaerGuest

As the hippy would say, "Heavy, man!".

10. ### Paul Hovnanian P.E.Guest

Hmm. I thought that was due to the gravitational attraction to