Re: Can this be true?

[Leigh Palmer <palmer@SFU.CA>]

At 08:37 -0700 8/11/99, Carl C. Gaither wrote:

> While working on the books I came across the following quote.  It seems
> to me to be quite an interesting statement.  Does anyone know if this
> can actually be a true statement?  The statement is:
>
> If a piece of string were exactly the same all along, however thin it
> was, however great the weight hung on it, and however much you jerked
> it, it could not break--it wouldn't know where to break.

I took a shower immediately after posting my reply to this question.
It occurred to me that the question is a wonderfully evocative one,
a question which can be given to kids learning science which will
both challenge them and encourage them to ask questions of a teacher
who is suitable prepared. A few of my supplementary thoughts are
given below:

1. A carbon nanotubule is, perhaps, the nearest realization of such
a string to be found in nature. Carbon nanotubules are very strong,
but they break.

2. The author does not seem to have allowed for elasticity. The
string will surely stretch, and to preserve its hypothetical
translational invariance and cleave to atomism as well, at the
greatest extensions one would expect to find a string consisting of
single atoms periodically disposed along a line with astronomical
separations.

3. The author doesn't know about inertia and finite sound speed. If
one were to jerk the string the tension in the string would no
longer be invariant - the string would break at the point of
greatest tension.

4. The jerk mode also gives one a way to introduce the ideas of
relativity and the notion of simultaneity.

...etc.

If you can get a small class going on a question like this good
things happen. I envy you teachers to whom this might actually be a
possibility. I'm looking at teaching a class of bright students who
are required to take an introductory course. Many of them don't
want to be there, and with 335 students (the room is full)I am not
likely to experience many teachable moments brought on by
spontaneous curiosities during lecture.

I'm off to watch meteors with the Mallinckrodts tonight!

73,

Leigh