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Cindy Schwarz TPT editorial, was Re: free fall data repost




comment on Cindy's note begin below, after my response to Joel's words.

At 12:33 PM 9/15/97 -0600, Joel wrote:

The physics is in the interpretation and
understanding of the graphs. Drawing graphs is important too, but it is a
separate skill.

I must disagree here. There is a lot of good physics in analyzing the
free-fall spark tape witha meter stick and doing the successive
differences
by hand. It really brings to life boring statements like delta X over
delta
T is the average velocity over an interval, in a hands on way (in the
best
tradition of hands on active style learning). Lot's of physics is in
areas
other than interpreting and understanding the graphs!!

There's plenty of good delta x / delta t stuff to do while analyzing
graphs; beginning with the graphical representation doesn't preclude going
to the definitions. Indeed, a thorough treatment requires it. And, it is
thoroughly hands on in that the students are extracting numbers from data
table or graph and calculating with them. It all depends on how one uses
the tool. MBL/CBL can be used badly, no question about it.



The computer of
course has to do this as well, but since it is all automated this fact
tends
to be totally obscured in the CBL's I've seen. Just telling the students
what the computer is doing doesn't cut the mustard as that is too passive
of
a learning situation in the laboratory.


Your're right, it isn't enough to just tell the student what's going on,
and a good lab does much more than that. Probably the best published uses
of MBL are the Real Time Physics labs. Those are very active, and require
the student to really understand what is going on behind the scenes.
Doing it right with CBL takes more effort to be sure, but it can be done.
You're hampered by using a tool with 0.032 megabytes memory.

So, well taught, there's no physics lost in the MBL approach in terms of
application of definitions and basics. The physics community is only now
learning how to teach with these tools.

What is gained? Plenty.

-There's the advantage of the real-time correlation between graph and
motion.

-There's the advantage of rapid repetition of experiments. One can ask
"what if?" and try something a little different.


It's the latter that really makes the technology superior. Rather than
spending a whole lab period analyzing one motion, you can consider all
sorts of variations. (an aside: I don't even like spending much time on
measuring g. The motion is too rapid to see clearly, so why not measure an
acceleration in a system that moves slowly and changes slowly enough to
visualize it as well? The concepts are the same.) With a good dynamics
cart and a motion detector you can look at the up/down motion, changes in
the acceleration in the trip up and down due to friction effects, changes
in graphs due to changing the initial velocity, the acceleration, the
position, changing the coordinate system by changing the position of the
motion detector.... Tons of things. The technology allows students to
behave like a scientist, pursuing the edges of the phenomenon, trying it
again and again to see what really makes the system work. It becomes
possible to explore much more of the parameter space. Even better,
students can be asked to predict in a sketch what will happen if we change
this or that parameter. Then do the experiment.

And the basic physics is NOT lost. Why then, put students through a manual
lab such as the Behr freefall experiment? Why just look at one motion when
you can look at ten?

Did anyone see the commentary that Cindy Schwarz wrote for the TPT that
just arrived? Great food for thought. I won't comment just yet on the
contents, but call everyone's attention to it. The discussion will
continue, I'm sure.

There are still lots of students with saddle sores.

JEG

__________________________________

John E. Gastineau gastineau@mindspring.com KC8IEW
900 B Ridgeway Ave. http://gastineau.home.mindspring.com
Morgantown WV 26505 (304) 296-1966