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Re: Hourglass Question

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On 9/6/2017 1:39 PM, Ron Hardin wrote:
> Ron Hardin wrote:
>>
>> An old question from the 1970s that I never
>> figured out.
>>
>> What governs the speed of flow of an hourglass?
>>
>> I mean what principle.  What's going on.
>>
>> It's not viscosity (no transport of x momentum in
>> the y direction etc.)
>>
>> It seems like it's the time it takes something to
>> call out of a lockup condition and clear the mess,
>> leaving it up to the next lockup condition, but
>> what the hell equation is that?
> 
> 
> Try this start: the sand above the hole consists of locked up unstable structures, each
> stabilized by the structure below it.
> 
> The one at the bottom goes unstable and falls, freeing the one above to begin going
> unstable.
> 
> So there a distance between structures, an instability growth time to collapse.
> 

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).

Here are the other factors that affect the accuracy of an hourglass:

     The amount or volume of sand used
     The size and angle of the glass bulbs
     The quality of the sand or granular material. It must be fine, dry 
and consistently formed so it can flow smoothly. (Some substances used 
in the past were fine grain sand, powdered eggshells, and powdered marble.)
     The width of the neck
     A tight seal so no moisture can get into the chambers. Moisture can 
add weight to the sand or clog up the neck.
     A flat and level surface on which to rest the hourglass

https://plus.maths.org/content/sand-through-hour-glass


this is the best;

https://www.inf.utfsm.cl/~amoreira/orzelc.pdf



https://www.technologyreview.com/s/418993/the-mystery-of-sand-flow-through-an-hourglass/

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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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