## PSN-L Email List Message

**
Subject: Re: Zero-length spring**

From: John or Jan Lahr JohnJan@........

Date: Wed, 29 Nov 2006 23:20:45 -0800

At 10:29 PM 11/29/2006, you wrote:
>Hi John, I am not too good at math, could you please plug-in some
>examples/numbers for this formula so I can understand it better? I
>think its k that I am unclear of. I understand the rest. Thanks, Ted
>MgA = kSY/(SA)
>
>M = kY/(Ag)
k is the spring constant. In this example I'm using k = 2 newtons/cm
M is the mass
Y is the height of the mast
A is the length of the boom
g is the acceleration of gravity
The exact numbers don't really matter - the point being that the mass
will be stable at any angle of the boom.
There are problems of trying to actually build this device, because
slight changes in k with temperature will cause instability. Even
without a zero-length spring, one can extend the period by reducing
the height of
the mast. However, you will soon discover that this will also lead
to instability if pushed to too long a period.
Cheers,
John
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