Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] motion problem





Hmmm...weight as usually measured includes the effect of std atmospheric pressure.
But this pressure drops a little with height.
This is to sketch the idea that a nitpicker might not concur with choice e.

Brian W


Bernard Cleyet wrote:
People!

I find it curious that buoyancy is so ignored. I read in elementary school about the Greek scientist who, on using it to solve the content problem of the ruler's bauble, ran naked. Now evidently it's even ignored by the authors of an applicable use in the current issue of the "The Physics Teacher".

bc not only a pedant, but a critic, and he wonders if he's turning into a Hake

p.s. When did you-all learn about buoyancy? One form of intelligence is the ability to use information from different fields or topics to solve problems, no? Should "we" be "teaching" intelligence or just rote learning?

p.p.s. I'm reading Banesh Hoffmann "The Tyranny of Testing". Banesh shows quite effectively the failure of multiple-choice, sentence completion, best paragraph selection, etc. tests. The majority of his examples are from the ETS.

From the cover blurbs (Dover ed. 2003 with an additional Jacques Barzun forward -- original 1962):

"Hoffmann's complete and well-documented account of the failings and dangers ... illustrates the inherent flaws in ... achievement tests. It demonstrates the inadequacies of multiple-choice testing, in which candidates simply choose answers and need not justify their replies, revealing the tests' inclination to reward superficiality rather than subtlety and creativity." [bc's emphasis]

---------------------------------------------------------

This question seems fine to me, with A being the correct answer. It seems
this question would be posed during a unit on dynamics, with things like
buoyancy coming later in the semester. To me, choosing E seems pedantic for
our purposes here, namely, teaching basic dynamics to high school students.

John Reed
Saint Mary's College H.S.
Berkeley, CA

----------------------------

I think it's a great question, because it affords a "teachable opportunity". If I were Jason, I would first explain it's not a "plain old" multiple choice question, but an opportunity for the class to think carefully about the question. They must supply a diagram and discuss it. If they successfully do (not including buoyancy, but including the absence of drag), I'd give nearly full credit. Those who include buoyancy (E), etc. get a bonne note! [sp. corrected] Doing so also affords a discussion of horological pendula. The better ones, not isolated in a vacuum chambre, include an aneroid bellows compensator. So technology meets physics. [better: physics informs technology]



bc pedant.

The original post:
>
> On Oct 28, 2009, at 1:24 PM, Jason Westfall wrote:
>
> Hi All,
>
> I had this as a question on an exam, and had a hard time convincing the
> kiddos of the correct answer. Could someone help me to explain it in a
> different way?
> Thanks.
> J. Westfall, Sonora High
>
> A rock is thrown up from the earth's surface. Which one of the following
> statements concerning the net force acting on the rock at the the top of
> it's path is true?
>
> A. The net force is equal to the weight of the rock
> B. The net force is instantaneously equal to zero newtons
> C. The net force's direction changes from up to down
> D. The net force is greater than the weight of the rock
> E. The net force is less than the weight of the rock, but greater than zero
> newtons.
>