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: Air resistance



On Sat, 13 Dec 1997, LUDWIK KOWALSKI wrote:

... That is why I am not totally convinced that my original analysis of
data (b=2 +/- 20%) [I assume you meant "n"] was really wrong. Perhaps
this stupid black box is not so stupid after all. There is no doubt that
the data on v and a are of "lower quality that the data on d". That is
why we have 20%. And I would yield easilly if somebody insisted that 20%
is too optimistic and 30% is better.

O.K. then; if that's really all it will take, I hereby *insist* that 20%
is too optimistic, especially if centered on n = 2 where it doesn't *even*
include the best fit value of n = 2.9! Since that is the case 30% is
clearly "better." But the fact remains that, on the basis of your
original data, the uncertainty in "n" is *far* larger than that, with the
95% confidence range probably extending from less than 1 to greater than
5. I have previously explained why in some detail. (BTW, where *did* you
get your 20% value anyway? I never understood that.)

But 1000% (b=0.2 --> 2) or 250% (from b=2 --> 5) is too much.

Why? On what *basis* do you make this claim? Let's see some uncertainty
analysis.

What else can I say? I do not think that the question, "how bad these
data are ?", has been definitely answered.

Oh, I'll answer that question. I think your basketball data (and I mean
the *data*, not the calculated values of v and a) are *extraordinarily*
good. After all, they appear to have an accuracy of less than 1 mm! I
have not used a sonic ranger myself, but I can't imagine getting much
better results with one.

The data are not as good as we would like them to be but how can they be
so bad?

Just to reiterate, the data are not at *all* bad. But the fact remains
that they don't *begin* to be sufficient to determine "n" with any
precision. This is primarily because the data are taken over far too
limited a range of velocities.

John
-----------------------------------------------------------------
A. John Mallinckrodt http://www.intranet.csupomona.edu/~ajm
Professor of Physics mailto:ajmallinckro@csupomona.edu
Physics Department voice:909-869-4054
Cal Poly Pomona fax:909-869-5090
Pomona, CA 91768-4031 office:Building 8, Room 223