Re: [Phys-L] Nice question on buoyance and balance

[John Denker <jsd@av8n.com>]

On 01/29/2014 02:36 AM, Savinainen Antti wrote:
> a former studen of mine send me a link to a nice question: 
> <http://wealthmanagement.com/question/puzzler-odd-balance>.
>
> I usually ask a variation of this question in my class. It is, in my
> opinion, a good example of conceptual reasoning which goes well
> beyond rote memorization. Probably many of you have seen this
> question before but I thought it might be worth sharing.

I put that in the category of problems that are very much
easier to solve in terms of momentum flow, as opposed to
force balance.  
 ++ I was able to solve it at a glance, in a fraction of a 
  second, using the momentum-flow approach.
 -- I had to think about it for a while to figure out a
  solution based on force-balance.

The connection between force and momentum-flow is spelled
out here:
  http://www.av8n.com/physics/force-intro.htm

===

Note that a goodly number of the FCI questions are in the
same category.  They go from "Huh?" to "Duh!" when translated
to momentum-flow language.

More importantly, a tremendous number of real-world tasks
are in the same category.  For example, fluid dynamics is
formulated in terms of the momentum transfer from one
parcel to another.  I reckon it is "possible" to formulate
it in terms of the force acting at the boundary between
one parcel and another, but that would be sheer masochism.