Re: [Phys-l] Definition of upthrust or buoyancy

["Jeffrey Schnick" <JSchnick@Anselm.Edu>]

Carl Mungan has a nice article on this entitled 
   What is the buoyant force on a block at the bottom of a
beaker of water?
and available at:
http://www.usna.edu/Users/physics/mungan/Publications/FEd3.pdf
I disagree with his conclusion in that in the example he gives the
buoyant force as he defines it becomes a ficticious force which is
partially countered by another ficticious (suction) force.
Pedagogically I think it's better to state that Archemdes Principle is
applicable over a limited set of circumstances, namely when the fluid is
in contact with all parts of the submerged surface of the submerged
object.  You can find an argument in favor of the net effect of the
pressure of the fluid definition for the buoyant force by going to
http://en.wikipedia.org/wiki/Talk:Buoyancy
and searching on:
Most of you seem to be missing the physical mechanics of buoyancy

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of
carmelo@pacific.net.sg
> Sent: Tuesday, October 19, 2010 3:41 AM
> To: phys-l@carnot.physics.buffalo.edu
> Subject: [Phys-l] Definition of upthrust or buoyancy
>
> Dear all,
>
> Upthrust or buoyancy is defined by some as the upward force on an
> object produced by the surrounding fluid (i.e., a liquid or a gas) in
> which it is fully, or partially immersed, due to the pressure
> difference of the fluid between the top and bottom of the object.
>
> However, this definition has a problem: If the object is at rest at
> the bottom of the ocean floor (assuming tight fit) with no fluid at
> the bottom of this object, do you agree that there is no upthrust or
> buoyancy for this situation?
>
> Upthrust or buoyancy should be better defined as the magnitude of the
> weight of fluid displaced by the body instead?
>
>
> Best regards,
> Alphonsus
>
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