## PSN-L Email List Message

Subject: Long Period Pendulum
From: tchannel1@............
Date: Sat, 23 Feb 2008 13:38:03 -0700

```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 =
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 =
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 normal.

Thanks, Ted

Hi Folks,   I set up another =
test in the=20
shop for the "Nearly Balanced Pendulum"   This time I =
found I=20
could only get about 15 seconds, using a 48" dowel with a center pivot =
at=20
24".   Here is what I found:

As I moved the top mass closer to the =
end of the=20
dowel, which countered the fixed lower mass, the dowel's balance=20
point would start to move from vertical to horizontal.

With no mass on the top, the dowel was =
vertical,=20
because of the lower mass.   Placing the top mass at about =
half way=20
up, the top half of the 48" dowel, the whole thing still remained=20
vertical.  As I moved the top mass higher, the dowel started to =
favor a 45=20
degree balance point, and a longer period, about 6 seconds.
The higher I moved the top mass, the =
longer the=20
period, but now the balance point was getting close to =
horizontal.

I maxed out at 15 seconds, and the =
dowel nearly=20
horizontal.   If I used a longer dowel I guess I would get a =
longer=20
period.

Q.  1.  This movement from =
vertical to=20
horizontal, it this expected?  or should it remain vertical as the =
period=20
get longer?
Q   2.  Should I get =
more than 15=20
seconds, by using finer adjustment of the top mass?  I would think=20
infinite.

My goal here, is to keep the dowel =
vertical, so if=20
I swing it, it will return to vertical, yet obtain the longest =
period. =20
With this experiment, I can keep it vertical, but only achieve less than =
10=20
seconds period.   Of course I want to use the shortest =
possible,=20
pendulum, say 48"

Not sure if it is my set up, or perhaps =
my=20
adjustments are still too coarse, or if this movement from vertical to=20
horizontal is normal.

Thanks, Ted

```