Re: Centrifuge

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Referring to my draft John Denker wrote:

> There's a lot more to the story.  ...

I agree. But, in my opinion, it was sufficient to describe
what is going on in a meaningful way. I wander what other
physlers think about this.

> The downward force goes like the cube of the radius.
> According to Prof. Stokes, the viscous force depends on ....

Yes, but this is in Chapter 9. In Chapter 7 I prefer to call it
"the water resistance force". Keep in mind it was a attempt to
produce a qualitative description of a simple centrifuge.

> As discussed above, thermal zig-zagging is not "the" explanation.

How do we decide what is and what is not an explanation?

> For that matter, for really small particles, they don't fall _at all_.
> If you start them out at the bottom, they will diffuse upward.

True, but why was it necessary to say so?

> > 3) The next step is to create a good quantitative problem
> > based on the preparatory description.
>
> It depends on what the objective is.

My objective was (and still is) to produce together a better
problem than the one formulated by S&F. I was not able to
advance beyond a qualitative preparation and I am waiting
for help. Or for an agreement that a quantitative example
should not be given before Chapter 9. The problem should
illustrated concepts introduced in Chapter 7, as intended
by the authors of the textbook. Perhaps our efforts will
help to improve something in a textbook. Being critical
is good, being constructively critical is better.
Ludwik Kowalski