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-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Wednesday, January 29, 2014 2:10 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Nice question on buoyance and balance
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.
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