## PSN-L Email List Message

Subject: Re: Different types of Pendulums
From: ChrisAtUpw@.......
Date: Sat, 27 Oct 2007 17:44:22 EDT

```
In a message dated 27/10/2007 22:23:56 GMT Daylight Time,
tchannel1@............ writes:

Hi Folks, Sometime in the past I saw a web site  describing different types
of pendulums used in sensors.  I don't  remember their names, but

1.  one was a long vertical rod, with a  center pivot, it contained a mass at
the top of the rod and a mass at the  bottom of the rod.

My question has to do with 1.  I thought  this pendulum (positioned like an
airplane propeller) was able to adjust it's  period by moving the top and or
bottom mass, up or down the rod?
I made a simply mock up of this illustration, but  was not successful in any
way. Can one adjust  this arrangement to result in an extended period? Does
anyone know of this web  site or one similar?

Hi Ted,

There are several possible systems, but you need to  suspend the pendulum
near the middle, a small height above the centre  of gravity. This gives a
high moment of inertia due to the masses at  the ends and the small restoring
force due to 2x mass operating just below the  suspension axis. It should work
fine. You can also vary the position of one  of the masses.

Regards,

Chris Chapman

In a message dated 27/10/2007 22:23:56 GMT Daylight Time,=20
tchannel1@............ writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
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Hi Folks, Sometime in the past I saw a we=
b site=20
describing different types of pendulums used in sensors.  I don't=20
remember their names, but

1.  one was a long vertical rod=
, with a=20
center pivot, it contained a mass at the top of the rod and a mass at the=20
bottom of the rod.

My question has to do with 1.  I tho=
ught=20
this pendulum (positioned like an airplane propeller) was able to adjust i=
t's=20
period by moving the top and or bottom mass, up or down the rod?
I made a simply mock up of this illustrat=
ion, but=20
was not successful in any way. Can one=20=
adjust=20
this arrangement to result in an extended period? Does anyone know of this=
web=20
site or one similar?

Hi Ted,

There are several possible systems, but you nee=
d to=20
suspend the pendulum near the middle, a small height above the centre=20
of gravity. This gives a high moment of inertia due to the masses=20=
at=20
the ends and the small restoring force due to 2x mass operating just below t=
he=20
suspension axis. It should work fine. You can also vary the position of=
one=20
of the masses.

Regards,

Chris Chapman
```

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