Re: cantilever versus arch

[Jack Uretsky <jlu@HEP.ANL.GOV>]

On Sun, 27 Jan 2002, John S. Denker wrote:

> At 11:08 AM 1/27/02 -0600, Jack Uretsky wrote:
> > Ahh, but simply stacking blocks on top of each other does
> > not a cantilever make.
>
> OK, that's almost a truism.  But folks do not learn much from truisms.
        So, when you have explained what you mean by "almost" we can begin
a dialogue -or end one.

> Was this statement offered in support of the notion that a
> cantilever is half an arch, or half an arch is a cantilever?
> If so, please supply the missing steps of the argument,
> because I'm not getting it.
        Neither.>

> Sure, simply stack blocks on top of each other does not make a
> cantilever.  It also doesn't make an arch.  It also doesn't make
> the Taj Mahal.  What does that prove?
        It demonstrates that you need to include the constraints.  Are the
blocks glued to each other, or simply loosely stacked.  In the version
that was originally given to me, we are considering one-half of an arch.
That was not stated, so the statement of the problem was incomplete.

> > The point is, when you state the problem please
> > include the constraints.
>
> Well, that's good advice, but I say again that the
> cantilever problem is well posed without any reference
> to arches, contrary to what some people have repeatedly
> asser
>
> The usual version goes like this:  Stack N uniform rectangular
> blocks so that they stick out over the edge of the table as
> far as possible.  Then say how far that is, as a function of N.
>
> Nitpickers are responsible for whatever additional conditions
> they feel necessary:  Homogeneous gravitational field, no
> friction, no crazy glue, et cetera.
        Of course the presence or absence of glue amounts to much more
than a "nitpick".
                                                Regards,
                                                        Jack

--
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It is your strength against my intelligence.  It is a veritable potpourri
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