[Phys-l] sticky toothpaste

[John Denker <jsd@av8n.com>]

On 11/07/2010 07:52 PM, Scott Orshan wrote:

>  I keep saying the same thing in different ways.

No, not the same thing.  Lots of different things.  About a
third of the statements are true, but they are soon followed
by other statements that contradict each other and violate
the laws of physics.

> > > > So please explain why I do not observe any flow.
>
> Air pressure, holding the funnel and plate together?

That is not an explanation.

It is wrong physics to focus on the vertical action of the
pressure "holding the funnel and plate together" to the 
neglect of the horizontal action pushing them apart.
Pressure is a scalar.  It acts equally in all directions.
Maybe the lateral edge of the glue layer so thin as to
escape your notice, but I assure you the air will notice.

So, without the stickiness of the paste keeping the air 
from coming in sideways, air pressure would have no role
in keeping the objects together.  Invoking "air pressure"
while denying stickiness is just wrong physics.

I have consistently said that under the conditions of the
experiment, toothpaste is sticky.

Or is the point to teach me the wikipedia definition of
thixotropic?  I'm not interested.  I have consistently used
the word the way it is used by experts in the field, which
(not coincidentally) agrees with the dictionary definition.
I don't care what wikipedia says, and FWIW it contradicts
itself on this point.

> an experiment in a vacuum to see if toothpaste can act 
> as a sealant

That experiment is not worth doing.  We all know that the
water in the toothpaste would instantly evaporate, pushing
the plate away.  Also, as previously explained, there are
far easier experiments that would be more informative.