# Re: <7E77C030-4F90-4434-A668-531C90C285AA@ucar.edu>

From: tiffani <tiffani_drew_at_nyahnyahspammersnyahnyah>
Date: Thu Oct 17 2013 - 08:59:04 MDT

On 10/16/2013 11:00 AM, ncl-talk-request@ucar.edu wrote:
> Hi all,
> I am still waiting for some one to answer the problem of the spinning
> disk, did I over tax you?
> Here is how some one else has worded the same problem:
>
> You have a compact disc rotating at a constant speed. The outer-most
> edge of the compact disc is rotating at, say, 20 km/h. Thus, the
> inner-most edge of a compact disc is also rotating at 20km/h. It is
> easily noticeable that the outer edge is traveling a longer distance
> than the inner edge, but if this is true, then the speeds should be
> different (the outer edge should spin faster, as it has to cover more
> distance in the same period of time). But saying that the outer edge
> spins at a higher rate is also wrong. I tried this out with a paper disc
> and made two markings (one on the inner edge and one on the outer edge)
> on a straight line, and after spinning the disc for a while, the
> markings were still in line with each other. If one of the edges had
> spun faster than the other, the paper would have been ripped to pieces!
> This simple experiment proves that the outer edge spins no faster than
> the inner edge. This question seems unsolvable to me. I know that there
> must be a mathematical explanation, but what?
>
>
> ------------------------------
>
> Message: 4
> Date: Tue, 15 Oct 2013 14:31:32 -0600
> From: David Brown <dbrown@ucar.edu>
> Subject: Re: ncl-talk Digest, Vol 119, Issue 19
> To: tiffani <tiffani_drew@yahoo.com>
> Cc: ncl-talk@ucar.edu
> Message-ID: <7E77C030-4F90-4434-A668-531C90C285AA@ucar.edu>
> Content-Type: text/plain; charset=us-ascii
>
> Well, yes you are over-taxing us, because this is not a question about the use of NCL or even software in general, and we are not a math
> discussion group. Nevertheless, I will attempt to answer this one time.
>
> The speed of a rotating object is often treated in terms of revolutions per minute. The RPM of the inside and outside of your disc is exactly the same.
> However the distance traveled for a point on your disc depends on the radius (distance to the center) of that point. A point on the inside has a smaller
> radius than a point on the outside. For each revolution the point travels 2 * PI * radius. (PI is about 3.14). So the problem is perfectly solvable.
> -dave
>
> On Oct 16, 2013, at 9:54 AM, tiffani <tiffani_drew@yahoo.com> wrote:
Thank you Dave
I am sorry about that (overtaxing you), I was trying to use Ncl to
assist with modeling of specific whether patterns, the question does not
not indicate that (my inadequacy), the idea is to interpret the
principles above to code for ncl which in turn can be interpreted to
assembly - c++ and 3ds Max to model the dynamics of galactic whirlpools.
Mr. G.Vandenberghe has resolved the problem for me and I also had some
assistance from the Department of Energy (Open Studio etc.). Thank you
again, in the future I will limit myself to matters within your
framework of understanding (When I learn how to frame my questions).
Tiffani Drew.
>

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Received on Wed Oct 16 13:00:22 2013

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