Re: [Phys-l] Finishing up with that Dead Horse.

["LaMontagne, Bob" <RLAMONT@providence.edu>]

First of all - I have no clue what "flexion" means.

However,  The force that the aquarium bottom exerts on whatever is touching it under the "shadow" of the lead cube seems to break down into 3 simple case - and an infinite number of fuzzily defined ones.

1) The lead cube is suspended by a cable above the aquarium floor by about 1/4 inch. The force against the aquarium flloor - and its force upward against the water is PB (pressure of the water at the level of the bottom of the tank but away from the vicinity of the cube) times the area of the shadow ..... PB*A   

2) The lead cube (maybe 4 inches across) held up from the floor of the tank by 4 quarter inch diameter dowels. The upward force from the portion of the tank under the shadow is Mg +PT*A-PB*A. Here M is the mass of the cube, PT is the pressure of the water at the top of the cube, and A is the area of the shadow.     (I am obviously neglecting the area of the dowels.)

3) The lead cube totally osculates the bottom of the tank excluding all water. The upward force from the portion of the tank bottom under the shadow is Mg + PT*A.


As far as what occurs for a "rough" surface - I have no clue until "rough" is defined.

Bob at PC

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Chuck Britton [cvbritton@embarqmail.com]
Sent: Wednesday, December 31, 1969 7:26 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Finishing up with that Dead Horse.

At 12:04 PM -0500 11/7/10, LaMontagne, Bob wrote:
> Change it from what? ---- Not having the lead cube there?

Some water under the cube (rough surface) and NO water under the cube.
Atomically close contact if you will.


> Bob at PC
>
> ________________________________________
> From: phys-l-bounces@carnot.physics.buffalo.edu
> [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Chuck
> Britton [cvbritton@embarqmail.com]
> Sent: Sunday, November 07, 2010 3:11 AM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] Finishing up with that Dead Horse.
>
> At 11:27 PM -0400 11/6/10, LaMontagne, Bob wrote:
> > Yeah - you're right - I just had to poke at that old hornet's nest :-)
> >
> > However, the "buoyancy" thread has been very useful. The fact that
> > so many people posted is a testimony to phys-lers passion for
> > understanding and getting things right. It's better to argue these
> > things out here among friends than to be unprepared when asked by
> > our students.
>
>
> And YOUR conclusion is - - - - - -?
>
> Does having a layer of water under the lead cube change the flexion
> of the bottom?
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