Re: Toilet bowl physics - Redux

[brian whatcott <inet@intellisys.net>]

This interesting observation of Ludwik's led to no great insights.
 My offering, for instance,  was a skit on general relativity and 
'notional forces'.

As it turns out, there is a recent effort to understand the apparently
anti-entropic clustering of small mobile objects in a suspension.

The collaboration from UPenn, UCSB, URochester NY, found that that
small polystyrene balls in water do not cluster when the balls have
 constant size. If a few balls of larger diameter are added, these 
latter start clustering at the edges in flat lozenges and hexagons.

  There IS in fact a notional force mediating this clustering which 
is called a 'depletion force.'
     Near a boundary, the smaller particles are excluded from
collisions with the larger particles and so they provide a boundary 
directed force.    On a macro scale, adjacent ships take care not to 
collide in a swell, where the swell provides the excluded center, so 
to speak.

 For a nicely written piece on this topic, see 'The Sciences'
 may/june 97 pps 15-  Physika - "Disorderly Conduct" H. C. von Baeyer

Regards
brian whatcott <inet@intellisys.net> Altus OK


At 08:59 AM 5/14/97 EDT, LUDWIK KOWALSKI wrote:
> I use an electric shaver (Philips) and empty it at once by throwing the 
> pieces of hair into a standard white porcelain toilet bowl (from an 
> elevation of about one meter).... their initial 
> floating distribution is nearly uniform. But then they start clustering 
> into "galaxies of short hairs". The overall picture after about ten or
> twnty minutes is quite different from what it was at the beginning. The 
> clustering seems to be faster near the rim where the bowl is shallower. 
> The grouping of hairs (about 0.5 to 1 mm long) is not total but some 
> tendency seems to be present. Or am I am expecting too much from 
> randomness?
>                                              Ludwik Kowalski
The classical explanation invokes a 'force' which attracts the stubble
according to its mass.
 The more modern interpretation is that isolated masses of this kind
distort space, in rather the way an elastic membrane would be distorted -
so as to provide a natural clustering effect without any force mechanism.

Regards
brian whatcott
brian whatcott <inet@intellisys.net>
Altus OK