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Re: [Phys-L] show the work +- movies +- conservation



I've now seen a couple of versions of the movie. It's really not so much a movie as an animated gif file.

In the movie that corresponds to your solution, on the left we start with a beaker of water with downward momentum (represented by little down arrows) flowing through it, in via gravity and out via contact of the bottom of the beaker with the pan of the pan balance. We add a table-tennis ball to the system and the flow increases a tiny amount. On the right, we start with an identical beaker of water (with the same original momentum flow) and a steel ball hanging by a string with downward momentum flowing through it, in via gravity out via the string. We lower the ball into the water and a significant portion of the momentum flow through the ball is redirected so that if flows into the water via the contact of the ball with the water. Significantly more downward momentum is flowing into the beaker-plus-water on the right, so that side goes down.

In the movie that corresponds to my solution, things are pretty much the same but on the right we start with just the beaker of water and we cause more downward momentum to flow into it by bringing a steel ball (part of the surroundings) into contact with the water.

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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 10:57 PM
To: Phys-L@Phys-L.org
Subject: [Phys-L] show the work +- movies +- conservation

On 01/29/2014 03:57 PM, Jeffrey Schnick wrote:

Thanks John.

:-)

I want to be sold on the momentum flow method so I am trying to see
what the advantage of it is. The short version of the force method
would be, "add the mass of a table-tennis ball to the left (the
internal forces don't matter) and push down hard on the right--the
right goes down." I got the impression that a short movie with little
down arrows flowing into and out of the beakers flashed into your mind
and you immediately saw the little down arrows flowing into the beaker
on the right faster. I wanted to see that movie.

I'd like to see the movie, too ... but I've never seen it.
Maybe some day I can make the movie, but the movie does not make itself.
...