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Re: Hourglass Question

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Serg io wrote:
> Fluid approximations do not work well at the scale of sand in
> hourglasses for most hourglasses. Almost all of the sand is statically
> braced against the walls and floor of the hourglass. Instead, you have a
> small region of instability above the hole where it is not possible for
> the sand to be braced; as that unstable portion falls through the hole,
> more falls in from above. There is slow flow of sand downwards, but it's
> still mostly statically braced. Thus, to a first approximation, flow
> rates are determined by grain size and shape (and material), and the
> immediate geometry around the hole (predominantly the size).

Thanks!  Did they get the sand bridges and instability the same way I did, by thinking about 
it, or is there a dynamic simulation somewhere?  It was wondering how to program a simulation 
long ago that first started the open question for me.  It wasn't and isn't obvious what to 
program, unlike say fluid particles or stars in a galaxy, or plasmas, where the particles can 
move independently of each other with the exception of neighboring particles or a global field.

Sand motion depends on a configuration over potentially long distances since the particles 
touch.

Incidentally, even with a fluid, the weight is supported by the sides of the container, with 
the exception of the column over the hole.  It's the indifference to pressure at the hole that 
distinguishes the two.  The sand bridges, if unbroken, don't let the pressure through.
-- 
rhhardin@mindspring.com

On the internet, nobody knows you're a jerk.

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Hourglass Question Ron Hardin <rhhardin@mindspring.com> - 2017-09-04 16:59 -0400
  Re: Hourglass Question Serg io <invalid@invalid.com> - 2017-09-04 17:53 -0500
  Re: Hourglass Question Double-A <double-a3@hush.com> - 2017-09-05 13:44 -0700
    Re: Hourglass Question benj <benj@nobody.net> - 2017-09-05 19:34 -0400
    Re: Hourglass Question "reber G=emc^2" <herbertglazier0@gmail.com> - 2017-09-06 14:22 -0700
      Re: Hourglass Question benj <benj@nobody.net> - 2017-09-06 18:21 -0400
        Re: Hourglass Question Serg io <invalid@invalid.com> - 2017-09-06 18:18 -0500
      Re: Hourglass Question hanson <hanson@quick.net> - 2017-09-06 15:35 -0700
      Re: Hourglass Question Double-A <double-a3@hush.com> - 2017-09-07 13:06 -0700
        Re: Hourglass Question Serg io <invalid@invalid.com> - 2017-09-07 16:44 -0500
          Re: Hourglass Question Double-A <double-a3@hush.com> - 2017-09-08 13:34 -0700
            Re: Hourglass Question "reber G=emc^2" <herbertglazier0@gmail.com> - 2017-09-08 15:53 -0700
              Re: Hourglass Question "hanson" <hanson@quick.net> - 2017-09-08 17:36 -0700
              Re: Hourglass Question Double-A <double-a3@hush.com> - 2017-09-11 14:41 -0700
            Re: Hourglass Question "reber G=emc^2" <herbertglazier0@gmail.com> - 2017-09-09 13:31 -0700
              Re: Hourglass Question "hanson" <hanson@quick.net> - 2017-09-09 14:32 -0700
  Re: Hourglass Question Ron Hardin <rhhardin@mindspring.com> - 2017-09-06 14:39 -0400
    Re: Hourglass Question Serg io <invalid@invalid.com> - 2017-09-06 14:01 -0500
      Re: Hourglass Question Ron Hardin <rhhardin@mindspring.com> - 2017-09-06 18:36 -0400
    Re: Hourglass Question jimp@specsol.spam.sux.com - 2017-09-06 19:26 +0000
  Re: Hourglass Question "reber G=emc^2" <herbertglazier0@gmail.com> - 2017-09-06 14:35 -0700
    Re: Hourglass Question Edward Prochak <edprochak@gmail.com> - 2017-09-06 15:32 -0700
    Re: Hourglass Question hanson <hanson@quick.net> - 2017-09-06 15:44 -0700
  Re: Hourglass Question "nuny@bid.nes" <alien8752@gmail.com> - 2017-09-06 15:50 -0700

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