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

[John Denker <jsd@av8n.com>]

On 01/29/2014 10:34 AM, Jeffrey Schnick wrote:
> I don't see how the momentum flow approach makes the problem simpler.
> I disagree with John Denker's statement that there are no other
> momentum flows crossing the boundary.  I think that on the steel ball
> side there is momentum flow from the steel ball, part of the outside
> world, across the boundary and into the system.  This momentum flow
> is associated with the contact interaction between the steel ball and
> the water.

That's a poor choice of "the system".

At one point I explicitly said to draw a dotted line around
the beaker.  Everything inside the dotted line is "the system".
The dotted line is the boundary.

On the left there are two flows crossing the boundary.  On the
right there are three.  Simple.

Previously I said I didn't see how to mess up the analysis.
Now I know.  You can mess it up by drawing a super-complicated
convoluted boundary.