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Re: [Phys-l] Student Misconceptions




On 2011, Sep 29, , at 10:08, Philip Keller wrote:

I ask these students to predict what the data will look like. Most common prediction (by far): three lines, of three slopes: low, medium and high. Then I make them predict the slope of the lines. Most pick three random but ascending numbers. Then I let them compare their answers. I will say that though only maybe 1 in 10 students has picked three identically sloped lines, once the others see that prediction, it is quickly recognized as most likely. Then they do the experiment and of course all three lines have nearly the same slope, all in the 9.8 neighborhod.

I think Philip should be a little careful here, as he's "talking" to some picky (not Picayune) Ph. D.s, as witness below.


On 2011, Sep 29, , at 10:21, John Denker wrote:


On 09/29/2011 10:08 AM, Philip Keller wrote:
The point is that most of my students believe that heavier objects
fall faster even after they have "learned" otherwise.

Well, actually they generally do fall faster. They don't fall
as /much/ faster as students think they do, so there's still a
misconception here that we need to deal with ... but IMHO we
ought not overstate the case.


Regarding the picket fence, the game is given away by "... all in the 9.8 neighborhood." A more correct statement for this expt. is, within the error (and here's a great opportunity to discuss error*** w/ the students) the three fall at the same acceleration. Then one uses the famous coffee filter experiment wherein the terminal speeds are plotted as a function the number nested, etc.

*** With a large number of students, an opportunity to see if the distribution is "bell curved", and more if AP ones.
bc wonders, what is the extrapolated terminal speed with "zero" filter?