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Re: [Phys-l] unbiased experiments--inquiry methods




----- Original Message ----- From: "John Clement" <clement@hal-pc.org>

Actually the students shouldn't "encounter" the equation, they should
determine it from the lab. The Modeling approach has them graph the data,
and if it is a straight line, just find the equation. If it is not, then
they try different ways to make a modified graph by changing the X axis. If
they have X vs t and it "looks like a parabola" graph X vs t^2 and see if
they get a straight line. This is a fairly old fashioned approach. Of
course the students have to follow some rules for taking the data so that
the data is analyzable by this approach. If it is a 1/sqrt(x) relationship
they have to first make a graph of 1/x and then by noticing the curvature
try 1/sqrt(x). So for most situations all they need is to recognize is
linear, inverse, square, and square root relationships.


Fine so far--this is pretty much where we first go with the pendulum experiment I described.
But then what? You end up with T = 2(L)^.5. You can deduce that the constant (about 2) needs units of seconds/(meters)^.5. Students can (do) see that gravity has something to do with the motion. I guess if you want to spend 3 periods on this you can work on the dimensional analysis, the 'guess' that the acceleration of gravity needs to be in there somewhere (although why the mass is not is going to be mysterious), and then play with the experimental constant and the units until you see an unexplained constant of about 6 floating around. That this constant is actually 2 pi might be deduced (if the original experiment is accurate enough) but this might be a big stretch for HS and gen-ed students. Connecting all this to SHM is yet another HUGE leap. Now our science/engineering students might get there, but with the content requirements of those courses, can one really spare the time? I really can't see the value after a point. Somewhere along the line one really needs to jump in with an equation. Reinventing the wheel once or twice is fine--but not for a whole curriculum. Students need to also know how to learn from books, from articles, from lectures--that is, from the learning paths that are available to them outside the structured classroom.

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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