Re: [Phys-l] Errata for FCI?

[Chuck Britton <cvbritton@embarqmail.com>]

Let me try to collect my thoughts here in public.
Nomex underwear is ON!

Any floatable object that doesn't float is subject to a net downward 
'sticky' force that prevents the floating. (This force can be - as we 
have seen - quite complicated - but it exists).

It seems to me that (the same) buoyancy acts on any submerged object.
I would like to think (but am quite willing to change my thinking) 
that the nature of the buoyant force doesn't change as the density of 
the object varies from less than, to greater than, that of the fluid.
.
At 9:34 AM -0400 11/3/10, chuck britton wrote:
> Thank you for resurrecting this 'sticky' subject.
> I have yet to see the concise argument against D.
> If we are going to use the term 'Bouyancy', do we need a definition
> other than the Archemdian 'weight of displaced fluid'??
> What might that new, PC (Pedagogically Correct) definition be??
>
> .
> At 9:00 PM +0800 11/3/10, carmelo@pacific.net.sg wrote:
> > Actually, I am still looking for a more appropriate microscopic
> > definition on buoyant force. Besides, it seems that many physics
> > teachers and physics education researchers have misconception on
> > buoyant force. Perhaps, there should be errata published for numerous
> > research papers on Force Concept Inventory (FCI)? Please refer to the
> > question below.
> >
> > A book is at rest on a table top. Which of the following force(s)
> > is(are) acting on the book?
> > 1. A downward force due to gravity.
> > 2. The upward force by the table.
> > 3. A net downward force due to air pressure.
> > 4. A net upward force due to air pressure.
> >
> > A 1 only.
> > B 1 and 2
> > C 1, 2, and 3.
> > D 1, 2, and 4.
> > E none of these, since the book is at rest there are no forces acting on it.
> >
> > In many papers on FCI, the answer is D based on the definition that
> > buoyant force is the magnitude of the weight of fluid displaced by the
> > body. Perhaps, analysis should be carried out again on FCI based on
> > the answer C instead? Some of you may prefer B to be the answer? :-)
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