PSSC and me
by Jim
Nelson
It seemed like an
easy task for a senior physics major at Lebanon Valley
College. Dr. Rhodes, my professor, had each of us in his
class select an experiment that had a significant historical
impact on human understanding of physics. We were
instructed to develop a presentation about the experiment,
to present it first to our classmates and then to students
in other physics classes. Since it seemed simple and
straight forward, I chose Young’s two-point interference
experiment. At the time I thought I did a nice job drawing
rays of light and then constructing similar triangles to
show that the wavelength of light waves (l)
can be calculated from other quantities that can be measured
(i.e., x, L, and d) using,
In retrospect, I
did not have a clue about what was really going on. Today
we might say I could do the problem, yet I was unaware that
I did not have a conceptual understanding of the situation.
And so it
remained for a couple or years. After graduation from
Lebanon Valley, I started graduate studies at Temple
University, but lack of financial support after the first
year led me to look for a job. It was late spring in 1961,
and, to my amazement, I was offered a position teaching
science at Harriton High School in Rosemont, PA.
For the first two
years I used a traditional physics textbook. Harold
Ferguson was the science department chair, and he was a
pilot teacher for the new CHEM Study chemistry curriculum.
He suggested that we visit Charles Smith, who was teaching
PSSC physics at Radnor High School in a district adjacent to
ours. The meeting date was established and on that day
Charlie Smith introduced me to the PSSC curriculum. I did
not know it then, but this meeting had a significant impact
on my teaching career. The next year I was using the PSSC
textbook, first edition, as my class textbook.
I loved the
textbook. It spoke to me like other textbooks did not. The
textbook told a coherent story rather than being an
encyclopedic approach that was the custom. The curriculum
reinforced for me the aspects of physics that I loved:
Physics is interesting, logical, and challenging.
As I look back
over my 45-year career as a physics teacher, I realize that
the greatest impact that the PSSC program had on me was the
philosophy of the PSSC laboratory component. The laboratory
approach was to present many questions, but with no blanks
to fill-in, encourage students to develop their own ideas
and methods, to consider the experimental design, and to
coordinate the laboratory activities with the textbook. The
laboratory activities stressed the nature of physics, the
importance of measurement, and the analysis of laboratory
data. In addition, the laboratory activities were very
creative, used simple and available equipment, and I
continued to use many of the laboratory activities for my
entire career.
I came to realize
that the leading edge of understanding for me as well as for
many of my students is rooted in experience. For students
learning physics this experience very often happens in the
laboratory. The “Preface for Students” in the PSSC
Laboratory Guide states, “This Guide is designed to help
you with your laboratory work. It provides a general
introduction to the problems at hand, gives you technical
hints, but leaves the thinking to you.” … “Throughout this
Guide you will find many questions. Finding the answer to
these questions may sometimes require a little thought about
what you have done before, or it may require a short
calculation. Sometimes more experimentation will be called
for. It is up to you to decide what to do in each case.”
The book was
divided into units and the second was “Optics and Waves.”
Later I learned that Charlie Smith along with Walter Michels
from nearby Bryn Mawr College had contributed a great deal
to the development of this section of the PSSC curriculum.
This became my all time favorite topic to teach and
laboratory activity II-12 was titled “Waves from Two Point
Sources.” To this day, I remember the first time I set up a
ripple tank and looked at the resulting dynamic two-point
interference pattern. The memory of my senior project came
flooding back to me. Suddenly a light bulb went off in my
head. I began to develop a conceptual understanding of
Young’s experiment, and it was so much clearer to me. I
have also learned that Young himself developed a ripple tank
demonstration to illustrate the experiment that now bears
his name.
In addition to
this specific epiphany, this experience reversed my thinking
about the role of the laboratory activity in teaching
introductory physics. I now believe the mantra “The
laboratory activity is the leading edge of the learning
experience.” The “Preface for Teachers” in the PSSC
Laboratory Guide states, “Most of the experiments in
this Guide are so presented as to pave the way for reading
the text. Thus, students can investigate physical phenomena
rather than just verifying known conclusions. When a
student performs experiments, the results of which are not
known to him in advance, he gains a feeling of personal
participation in the discoveries of science; both science
and the role of scientist become more meaningful to him.”
The first PSSC
Unit, titled “The Universe”, was an introduction to physics
as a human enterprise. The symbol of the American Institute
of Physics shows a pendulum, a cylindrical mass, and a
ruler. These are devices for measuring the basic physical
quantities of time, mass, and space, and the measurement of
these was stressed in Unit I of the PSSC curriculum. I
remember working with my students on laboratory activities
measuring the distance to the smoke stack at Villanova
University, using oleic acid to approximate the size of a
molecule, and using a vibrating timer to measure short time
intervals for the first time. Because the vibrating timer
is a transparent, yet powerful way to connect graphs to real
motion, the vibrating timer is still used by many teachers
as a way of gathering data and analyzing motion. Real-time
computer displays available today should not replace but
rather extend this experience for students.
Of all the
equipment inspired by the PSSC project, I was most taken by
the Slinky and ripple tank activities in Unit II. In all
there are six activities using a ripple tank that illustrate
the basic properties of waves. After the Young’s two-point
interference simulation in the ripple tank, laboratory
activity II-13 asks the students to do an elegant
reproduction of Young’s experiment using equipment that they
make themselves. The Slinky and ripple tank photographs
used in this unit on waves are shown in almost every
introductory physics textbook available today. Although we
can now supplement the teaching of one- and two-dimensional
waves with computer animation, the Slinky and ripple tank
are still important tools in the arsenal of the introductory
physics teacher. The use of the semicircular disk for
studying refraction of light by clear liquid is a gem. It
shows how simple equipment can lead to quite sophisticated
data analysis.
In
fact the entire waves and optics section of PSSC was
masterfully constructed to tell a story from the properties
of light as developed during the laboratory activities to
the models that explain these properties. This unit clearly
illustrates how newly discovered properties lead to
modification of the models used to represent light, and how
the models lead to uncovering new properties of light. In
essence, when using the PSSC curriculum, a student becomes a
"junior physicist" discovering the wonder and rhythm of
nature.
Other PSSC
laboratory activities helped me and my students develop an
understanding of the nature of physics and have become
staples in contemporary introductory physics teaching. The
laboratory for PSSC Unit III, Mechanics, originated
unique and today ubiquitous activities, including the
introduction of the dynamics cart that is so common today,
and expanded the use of the vibrating timer. The idea to
use rubber bands to apply and vary the force to accelerate a
dynamics cart was at once simple but very real to the
student. A complete analysis of uniform circular force and
motion was introduced using very common materials.
Conservation of momentum was introduced by spring explosion
between dynamics carts, and a delightful collision in two
dimensions was provided that produced exceptionally good
results for the students if they were careful and skillful
with the apparatus. The idea of the kinesthetic learner was
embedded in the PSSC laboratory activities long before this
was an educational “buzz word.”
PSSC Unit IV,
Electricity and Atomic Structure,
included laboratory activities on determination of Coulomb’s
Law, measuring the number of electrons in a coulomb, tangent
galvanometer to investigate magnetic fields, and the
measurement of the mass of an electron.
To say the least,
I loved the PSSC program. I feel it make a grand
contribution to teaching. With some of the most respected
university and high school teachers involved in its
development, PSSC changed the nature and role of laboratory
activities for high school physics and fanned the flames of
curriculum development in chemistry and biology in the 60’s.
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