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

Regarding #3, try sticking your finger in a beaker of water on a scale,
but do not touch the bottom. What happens to the scale reading? Try it and
see. My students are always amazed!

For those who may remember, I posed a similar question on Tap-L back in
February, 2004. It was the string and ping pong ball in a beaker of water
on a scale. If the string were cut and the ball then floated, would the
scale reading change?

These are great thinking questions that are very challenging for students
-- even my brightest ones. And when physics teachers argue back and forth,
you can only imagine what students think about these questions. I made
them bonus questions on tests. Few got them correct. Maybe better as a
demo or something.


Phys-L@Phys-L.org writes:
My thoughts...
1. The shape of the water isn't an issue.
2. The steel ball isn't adding any mass to the RHS.
3. It doesn't matter whether the ping pong ball is in the water or
floating on top. All those forces are dealt with within the beaker.
4. The ping pong ball is adding its mass to the LHS.
...left sinks.

I'd like to know John's momentum-flow approach. If I ever learned it,
I've forgotten it.

Dr. Roy Jensen
(==========)-----------------------------------------¤
Lecturer, Chemistry
E5-33F, University of Alberta
780.248.1808



On Wed, 29 Jan 2014 09:36:13 +0000, you wrote:

Hi,

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.

Regards,

Antti
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