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Re: [Phys-L] Another Fluid/Density 'Problem'



I’m not sure my students would have accepted this as an explanation of how there can now be greater fluid force acting on the bottom of the bottle.

Where did the extra force ‘come from’?


On Jan 29, 2014, at 8:41 PM, Brian Whatcott <betwys1@sbcglobal.net> wrote:

Pressure is proportional to head in a homogeneous liquid, where horizontal extent is immaterial.
Pressure changes where the less dense component occupies a greater proportion of the head because it is confined to a reduced horizontal extent. Which is to say - horizontal extents of components of differing density are material!

Brian Whatcott Altus OK

On 1/29/2014 4:51 PM, Chuck Britton wrote:
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An Old Fashioned Glass Milk Bottle with a narrow neck is delivered to your doorstep in the morning and because it is no(t) homogenized, the Cream has risen up into the narrow(er) region.

The fluid pressure exerted on the bottom of the bottle is (rho) g h.
Where (rho) is the average density of the column of milk/cream that extends from the top surface to the bottom.

Now we will thoroughly MIX the bottle of milk and we note that the average density of this same column of milk is GREATER than (rho). Let’s call this new density (RHO).

How can the pressure have increased while the area of the bottom has stayed constant?
How can we accept a greater amount of downward fluid force caused by ‘just’ mixing the milk?

(This is reprised from back in the last century.)
Probably presented better back then.
;-)
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_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l