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

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

Sorry Jeff, I shouldn't have said yes so quickly. You do have the mass of the ping pong ball (I assumed it to be zero). So you would have to put another ball on the right had pan to maintain equilibrium (you could float it on the water - or just put it next to the beaker).

Bob at PC

> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Jeffrey
> Schnick
> Sent: Wednesday, January 29, 2014 9:01 AM
> To: Phys-L@Phys-L.org
> Subject: Re: [Phys-L] Nice question on buoyance and balance
>
> That's interesting.  Are you saying that if all one did was to fasten the table
> tennis ball, with a string, to the bottom of the beaker on the left and do
> nothing to the beaker on the right (e.g. do not stick a steel ball in it) that the
> system would remain in equilibrium?
>
> > -----Original Message-----
> > From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of
> > LaMontagne, Bob
> > Sent: Wednesday, January 29, 2014 8:55 AM
> > To: Phys-L@Phys-L.org
> > Subject: Re: [Phys-L] Nice question on buoyance and balance
> >
> > The answer was almost instantly obvious from forces - The string on
> > the ping pong ball pulls up on the beaker, negating the buoyancy. The
> > left beaker has all internal forces - which must cancel.
> >
> > Bob at PC
> >
> > > -----Original Message-----
> > > From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John
> > > Denker
> > > Sent: Wednesday, January 29, 2014 7:33 AM
> > > To: Phys-L@Phys-L.org
> > > Subject: Re: [Phys-L] Nice question on buoyance and balance
> > >
> > > 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.
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