PSN-L Email List Message

Subject: Re: Long Period Pendulum
From: "Geoff" gmvoeth@...........
Date: Sun, 24 Feb 2008 12:20:41 -0700

Howdy tchannel1 & PSN,

It seems to me that even tho
you get a longer period this
way your sensitivity to motion
will be greatly reduced because
you are using masses that are
in opposition to each other.

I think in imperative to have
the mass be totally out of balance
with a pure force that is not a mass.
Thus only the sensor mass
will be involved in forces relating
to accelerational forces.

THE restoring forces will dictate the
free period.

Are you planning to incorporate this
pendulous device in some role
that is not the sensor itself ??

Maybe i am not picturing your verbose
ideas correctly even tho verbosity
is necessary in absecense of pictures?


----- Original Message ----- 
To: "psn" 
Sent: Saturday, February 23, 2008 1:38 PM
Subject: Long Period Pendulum

Hi Folks,   I set up another test in the shop for the "Nearly Balanced Pendulum"   This time I found I could only get about 15 
seconds, using a 48" dowel with a center pivot at 24".   Here is what I found:

As I moved the top mass closer to the end of the dowel, which countered the fixed lower mass, the dowel's balance point would start 
to move from vertical to horizontal.

With no mass on the top, the dowel was vertical, because of the lower mass.   Placing the top mass at about half way up, the top 
half of the 48" dowel, the whole thing still remained vertical.  As I moved the top mass higher, the dowel started to favor a 45 
degree balance point, and a longer period, about 6 seconds.
The higher I moved the top mass, the longer the period, but now the balance point was getting close to horizontal.

I maxed out at 15 seconds, and the dowel nearly horizontal.   If I used a longer dowel I guess I would get a longer period.

Q.  1.  This movement from vertical to horizontal, it this expected?  or should it remain vertical as the period get longer?
Q   2.  Should I get more than 15 seconds, by using finer adjustment of the top mass?  I would think infinite.

My goal here, is to keep the dowel vertical, so if I swing it, it will return to vertical, yet obtain the longest period.  With this 
experiment, I can keep it vertical, but only achieve less than 10 seconds period.   Of course I want to use the shortest possible, 
pendulum, say 48"

Not sure if it is my set up, or perhaps my adjustments are still too coarse, or if this movement from vertical to horizontal is 

Thanks, Ted


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