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Re: [Phys-l] Phys-l Digest, Vol 70, Issue 15



I barely even know what we're talking about any more, and I'm not sure of the point you're trying to make. When you push on toothpaste a little, it is viscous. When you push on it harder, it thins out and flows. When you're holding the plate with the funnel the toothpaste is not flowing. There's not enough shear force to thin it. Whether it is glue-like is a completely separate question, but I don't feel that toothpaste is particularly sticky. When I was looking for something to use as a sealant, I tried vaseline first, but that didn't work as well as toothpaste. Vaseline is much stickier than toothpaste.

>>So please explain why I do not observe any flow.

Air pressure, holding the funnel and plate together?

I don't really have any more to add to this discussion. I keep saying the same thing in different ways. If someone has something new to add here, or conducts an experiment in a vacuum to see if toothpaste can act as a sealant to prevent an object from floating upward, then I might join in again. Have fun.

* /From/: John Denker <jsd@av8n.com <mailto:jsd%40av8n.com>>
* /Date/: Sun, 07 Nov 2010 13:06:03 -0700

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On 11/07/2010 08:33 AM, Scott Orshan wrote:
I think I can have it both ways.

No, in any given experimental situation, you can't.

Am I wrong in observing that toothpaste will both hold its shape on a
surface, yet be slippery underfoot?

Under the conditions of the experiment, it's either one or
the other.

Specifically: I am holding the funnel which is supporting
the weight of the plate.

Under *these* conditions on *this* timescale the paste either
flows or it doesn't. Please tell me, does it flow or doesn't
it?

You have sent two messages emphasizing that it is not viscous,
not sticky, not glue-like, and not capable of supporting shear
stress. In that case, it would be energetically favorable for
it to flow. So please explain why I do not observe any flow.