Paul J. Dolan, Jr.*, 5709 Bennett Hall, Dept. of Physics and Astronomy,
University of Maine, Orono, ME 04469-5709, liquidhelium@hotmail.com.
Abstract
A qualitative lab exercise, suitable for students at all
levels, is presented. The goal of the exercise is to enhance the students’
observational and analytical skills, in determining the identity of a set
of objects, by studying the parts that remain when it has been violently
dissembled. An analogy is made to the reconstruction process that is used
in particle physics, when the existence and properties of high-energy particles
are inferred from the collision products.
Introduction
On a visit to a local accelerator lab, our tour guide likened the process of discovering new particles to throwing a watch at a stone wall, at high velocity, and then trying to determine the identity and properties of the particles formed, from the remaining decay products. This type of "finding the whole" while missing some of the parts, can be a useful exercise, and not only in the sciences. It occurred to me that one could construct a Qualitative Observation exercise for physics labs, using the ‘remaining parts’ of common objects. As an added benefit, this exercise found a useful after-life for some defunct equipment.
This was done for a ‘Gifted’ class ("Mysteries of Physics"),
part of a series of high-school level classes organized by the Chicago
Public Schools for seventh and eight grade students, using university facilities
and personnel1. This exercise was used in my "Mysteries" class
in the 1998-99 and 1999-2000 school years.
Preparation
Unlike the preparation and setup for many Physics experiments, the preparation for this one is quick and fun, once the objects to be observed have been selected. Ten small boxes were prepared with the ‘remains’ of the various items. Three of the boxes are not comprised of a specific ‘whole’: one box contained bit & pieces of pencils and chalk, while another had miscellaneous electronic parts (resistors, capacitors, etc.), and a third had unrelated pieces (a rubber glove, popsicle stick, bits of refrigerator magnets). The seven other boxes contained the crushed remains of the following: a toy car, a Xmas bulb tester, a dart gun, a stopwatch, a digital thermometer, a calculator, and an empty printer cartridge. Some of these were things that the students had used (when intact) earlier in the year. Pictures of several of the ‘remains’, along with an intact item, are shown in the figure.
All parts that could be considered hazardous (glass, batteries) were removed prior to crushing, as were any parts that would make identification too obvious (such as the face of the stopwatch).
Note on preparation: the plastic cases of common lab items,
such as the stopwatch, are remarkably tough, and it takes a considerable
‘impact’ to break into suitably small pieces!
The Experiment
The goal is simple: determine as much as one can about each collection of objects, based on one’s observations of the parts available, and try to deduce the ‘whole’ from which the pieces came. The ten small boxes were made available to each team of students for their inspection. While all remaining parts were deemed to be safe to handle, as a precaution and to emphasize good lab technique, the students were encouraged to examine the parts using a tweezers. Also, it was emphasized that only one box be examined at a time, so that there would be no mixing of the parts between different sets.
In the latest class to do this exercise, of nine groups
of students, all got at least 4 correct; the average number of correct
identifications being above 7. I believe the students found this to be
both a fun and useful exercise.
Conclusion
Most of the Physics lab exercises that we have the students
perform concentrate on using some specific piece of equipment, and on ‘taking
the data’; not enough time is spent in having the students work on their
observational skills. Here, I have presented a qualitative exercise that
can be adapted for science students at all levels, that hones the students’
observational and analytical skills, and that can performed with whatever
‘bits & pieces’ may be on hand. While the genesis of this idea may
have come from hearing about experiments in particle physics, the technique
of finding the whole without all the parts is certainly applicable to any
area of science, and beyond.
Acknowledgement
I would like to thank the "Gifted Program of the Chicago
Public Schools", the director of the program at NEIU, Professor Herb Stoltze,
and the students of "Mysteries of Physics", for making this opportunity
possible.
*Permanent address: Physics Dept., Northeastern Illinois University, 5500 N. St. Louis Ave.,
Chicago, IL 60625
(1.) The "Gifted Program of the Chicago Public Schools"
is run, among other places, at Northeastern Illinois University for students
in the seventh and eighth grades. Classes at NEIU include Chemistry, Biology,
Biochemistry, Physics and Algebra, and most are taught by university faculty.
Successful completion of many of these classes includes high school credit
for the course.
Figure 1: "Bits & Pieces" used in the exercise, and the corresponding ‘whole’; a.) Toy car, b.) Xmas bulb tester, c.) "Batman" dart gun, d.) Stopwatch, e.) Digital thermometer, f.) Calculator.
<<Figures will be posted later.>>