Re: vibrating bar supported by light string to reduce damping

[John Denker <jsd@AV8N.COM>]

Frohne, Vickie wrote:
> Others might joke about Thag and Oona, but I don't see this as an
> unreasonable request.  Most common sewing threads will be totally
> unsuitable because they have a built-in twist.  If you try to hang a
> heavy weight from a common thread, the weight is likely to spin and
> spin until the untwisted thread breaks.

If you use two threads, the problem goes away for typical
acoustic applications.  If you use two threads of opposite
helicity, an even wider class of problems goes away.

Both versions of this solution are older than history.
Hint:  rope ladder leading up to your cave.

> There is also the matter of
> getting the correct elasticity (don't want the mass bouncing) and
> strength (don't want it hitting the floor). For long-term
> observations you don't want the thread to twist or change length when
> the humidity changes, either. Presumably the reviewer would like you
> to provide a reference to a source of thread or string that is
> suitable for your application so that the reader can set up the
> experiment for himself or herself.
>
> These properties of thread are probably precisely why Cavendish
> resorted to a difficult-to-make quartz fiber for his balance.

Cavendish had much, much stricter requirements, because he was
building a torsion balance with super-low resonant frequency.
For supporting something undergoing audio-frequency vibration
(not low-frequency torsion), as was the original subject of
this discussion, the requirements are not nearly so strict.

If the referee wants a more detailed description of how the
threads are attached, that's fine ... but it's a description
issue, not a citation or credit/priority issue.

> (who makes thread Oona's way, and it's not that easy)

I never said spinning was easy.  In fact, to make contact with
today's other thr... (ahem) topic, you could argue for putting
Oona on the list with Newton and Einstein, in recognition of an
invention that was totally nontrivial and surpassingly important.

Still, according to well-established conventions, I am not
obliged to cite Newton chapter and verse every time I write
F=ma, I am not obliged to cite Einstein chapter and verse
every time I write x^2 + y^2 + z^2 = c^2 t^2, and I am not
obliged to cite Oona every time I use a piece of thread.