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Re: free fall data repost



I sent a shorter version of this 12 hours ago and it hasn't yet shown up,
so I'll send again. Sorry if it's a duplication.

At 07:13 PM 9/14/97 -0500, Lawrence wrote:

The old spark timer lab that
many of us used to teach had terrible acceleration graphs too.

I built a spark free-fall apparatus nearly 30 years ago. I use it with
a large induction coil and a half-wave rectifier. The apparatus looks
like a Rube Goldberg throwaway...but IT WORKS. I use 60Hz as the time
base and the ball falls about 1 meter I am able to consistently able to
get 'g' with less than 10% error.

True, with curve fitting or averaging of the acceleration values the old
spark timer experiment can give good values. Do you mean that the
acceleration values, calculated with simple successive differences as
Ludwik wants to do, were ALL within 5 or 10%? I'd be very surprised, but
my experience was only with the Behr freefall apparatus. Your equipment
may have been better. Still, even if the old spark timer experiment gave
good results, I'd never go back to it.

My point with the CBL data was to show that the precision is high enough
to use very simple analysis.

we need to get back to
those PSSC type of equipment days when we used simple equipment and
_Made it Work_ and learned the frustration that accompanies all 'real'
physics inquiries.

Spoken as a true Luddite.

I couldn't disagree more. I think that this is a prescription for turning
off yet another generation to physics, and for continuing teaching
practices that appear to be inferior as judged by the literature.

A couple of standard references: "Learning motion concepts using real-time
microcomputer based laboratory tools," Thornton and Sokoloff, AJP vol 58 p
858

"The effect of real time lab graphing on learning graphic representations
of distance and velocity," Brassel, JRST, vol 24, p 385ff.

These both showed that students doing kinematics experiments who had to do
more traditional style analysis learned LESS than those who had real time
computer graphing tools. The physics is in the interpretation and
understanding of the graphs. Drawing graphs is important too, but it is a
separate skill.

That's not to say that all experiments need to be done with technology.
There's no better way to start teaching electrostatics than with a roll of
adhesive tape for each student. Sometimes the technology is appropriate,
sometimes it is not. Use the right tool!

There is, though, no reason to make physics harder and more frustrating.

JEG

__________________________________

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