PSN-L Email List Message

Subject: Re: clock pendulums
From: Christopher Chapman chrisatupw@.......
Date: Wed, 23 Mar 2011 08:53:34 -0400 (EDT)

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Bryan Mumford ng1@............
Sent: Sat, 12 Mar 2011 17:23
Subject: RE: clock pendulums

I've seen earthquakes stop my clock pendulums. Presumably this is=20
ecause they shifted the ground in the direction the pendulum was=20
A clock at 90 degrees to the one that stalled kept running.
swingingThe quake in Japan was too far away to have such an effect, but I'm=
=20
hinking about the kind of motion the earthquake is likely to deliver=20
rom so far away. Will it be an up and down motion?
Is this a difference between P and S waves? Would it be a vertical P=20
ave from Japan, and a lateral S wave from a closer quake that might=20
tall a clock pendulum?
Hi Bryan,
P waves give a vertical displacement at right angles to the direction o=
f  propagation. Distant quakes are likely to have a=20
P frequency of about 1 Hz, but for local quakes it may be up to 10 Hz. Thes=
e are the fastest waves and the first that you receive.
=20
he S waves are lateral transverse waves which move horizontally, at right a=
ngles to their direction of propagation. They have about half=20
velocity and frequency of P waves. Distant quakes may have a frequency of 0=
..5 Hz, but local quakes can be up to 5 Hz.
You can download a free Seismogram manual with all the information that you=
are likely to need from http://psn.quake.net/info/analsis.pdf=20
=20
Thinking about it carefully, I would expect a pendulum clock to be most s=
ensitive to vertical waves. The rise and fall of the pendulum=20
is very small, say 1.3 thou" for a 1m device, whereas the sideways deflecti=
on may be over a couple of inches. Whether the pendulum action=20
is effected or even stops, depends on the phase and the frequency of the in=
comomg wave. The P and S waves are usually only a few cycles=20
long at most, not a train of waves.

Regards,

Chris Chapman =20
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Am I correct in assuming that your clocks use a vertical pendulum with a=
period between 1 and 2 seconds?=20
ryan Mumford

=
Bryan Mumford ng1@............
Sent: Sat, 12 Mar 2011 17:23
Subject: RE: clock pendulums

I've s=
een earthquakes stop my clock pendulums. Presumably this is=20
because they shifted the ground in the direction the =
pendulum was=20
.. A clock at 90 degrees to the one that stalled kept running.

swingingThe quake in Japan was too far away to have such an =
effect, but I'm=20
thinking about the kind of motion the earthquake is <=
FONT size=3D2>likely to deliver=20
from so far away. Will it be an up and down motion?

Is this a difference between P and S waves? Would it =
be a vertical P=20
wave from Japan, and a lateral S wave from a closer quake that might=20
stall a clock pendulum?

Hi Bryan,    P waves give a vertical displacement at right angles to=
the direction of  propagation. Distant quakes are likely to have a =
P frequency of =
about 1 Hz, but for local quakes it may be up to 10 Hz. These are the fastest waves and the first that you receive.
The S waves are lateral transverse waves which move horizont=
ally, at right angles to their direction of propagation. They have about ha=
lf veloc=
ity and frequency of P waves. Distant quakes may have a frequency of 0.5 Hz=
, but local quakes can be up to 5 Hz.You can download a free Seismogram manual with=
all the information that you are likely to need from http://psn.quake.net/info/analsis.pdf =
Thinking about it carefully, I would expect a pend=
ulum clock to be most sensitive to vertical waves. The rise and fall of the=
pendulum =
is very small, say 1.3 thou" for a 1m =
device, whereas the sideways deflection may be over a couple of inches. Whe=
ther the pendulum action is effected or even stops, depends on the pha=
se and the frequency of the incomomg wave. The P and S waves are usually on=
ly a few cycles l=
ong at most, not a train of waves.     Regards,     Chris Chapman   =
=
=
Am I correct in assuming that your clocks use a vertical pendulum with a p=
eriod between 1 and 2 seconds?
Bryan Mumford

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