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This is to certify that the

thesis entitled

The Effectiveness of Student-led
Demonstrations in a High School
Physics Class

presented by

Paul B. Ciske
has been accepted towards fulfillment

of the requirements for

Master of___S_ci_ence_degree inlntendepartmental
Physical Science

Major professor

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Date July 16, 2002

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6/01 cJCIRCIDateDuost-sz

 

THE EFFECTIVENESS OF STUDENT-LED DEMONSTRATIONS IN A
HIGH SCHOOL PHYSICS CLASS
By

Paul B. Ciske

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Division of Science and Mathematics Education
College of Natural Science

2002

ABSTRACT

THE EFFECTIVENESS OF STUDENT-LED DEMONSTRATIONS IN A HIGH
SCHOOL PHYSICS CLASS
By
Paul B. Ciske

During the 2001-2002 school year, the students in the physics class at Mio
AuSable High School prepared and performed demonstrations for their fellow students
on eleven physics topics: fluid mechanics, thermal energy, wave properties, sound,
reflection, electrostatics, dc circuits, Newton’s Laws, force components, circular motion
and rotational motion. Data were collected using predetermined pretest and posttest
questions to measure the effectiveness of using demonstrations in this way. Improvement
was also studied using a student opinion survey and collections of student responses to
test questions.

The data Showed considerable improvement by the students in the eleven topic
areas on the posttest compared to the pretest. The data were also examined to compare
the scores of the students who performed the demonstrations to those of students who
observed the demonstrations. The data showed that the presenters typically performed

better on the posttest than the observers.

ACKNOWLEDGMENTS

Many people have helped me over the past few years as I have completed this
Masters of Science program. I would like to acknowledge the efforts of the many fine
instructors at Michigan State University who have enhanced my understanding of science
and the uses of instructional technology. I am sure that I am a better teacher as a result of
their efforts. Specifically, I would like to thank my advisor, Dr. Merle Heideman, for her
patience and guidance during the composition of this thesis.

I would like to acknowledge the financial support that I received in the way Of
tuition assistance from the Towsley Foundation during the summers of 1998, 1999 and
2000. I would also like to acknowledge a stipend received from the National Science
Foundation through a Research Experience for Teachers grant during the 2001 -2002
school year. While this latter grant did not subsidize tuition, it did help to offset other
expenses incurred while completing the research in this thesis. I would also like to
acknowledge the generosity Of my fellow student, Phillip Ewing, and his family for
Opening their home to me on several trips to East Lansing for class work. Each Of these
helped reduce the financial burden of completing the Master of Science degree, and I am
very grateful. 2

Finally, I would like to acknowledge my wife, Karen, for her tolerance of my
absences over the past few years, including five weeks in the summer Of 2001 when She
cared for our newborn son on her own. Without her love and encouragement, I am sure

that I would never have completed this program.

iii

LIST OF TABLES ................................................................................... vi
LIST OF FIGURES ................................................................................ viii
INTRODUCTION .................................................................................... 1
IMPLEMENTATION ................................................................................ 8
RESULTS ............................................................................................ 20
DISCUSSION. .1 ...................................................................................... 30
APPENDIX A: EVALUATION TOOLS ........................................................ 35
A-I: SEMESTER ONE PRETEST/POSTTEST QUESTIONS WITH
EVALUATION RUBRICS ...................................................... 35
A-II: SEMESTER TWO PRETEST/POSTTEST QUESTIONS WITH
EVALUATION RUBRICS ...................................................... 43
A-III QUESTIONS REPEATED ON THE SEMESTER ONE EXAM .......... 47
A-IV: EXAMPLE HOMEWORK QUESTIONS .................................... 49
A-V: STUDENT OPINION SURVEY ................................................ 51 . "
APPENDIX B: PHYSICS DEMONSTRATIONS .............................................. 52
3-1: FLUID MECHANICS DEMONSTRATIONS ............................... 52
3-11: A COLLECTION OF HEAT DEMONSTRATIONS ....................... 58
3-111: YE OLDE RIPPLE TANK DEMO ............................................. 62
B-IV: RESONANCE: WE GOT THE BEAT ......................................... 74
B-V: THE LASER SPIROGRAPH ................................................... 71
B-VI: THE GREAT BALL OF DEATH .............................................. 76

TABLE OF CONTENTS

iv

B—VII: BE IT EVER SO HUMBLE, THERE’S NOTHING LIKE OHM ......... 82

B-VIllzNEWTON’SLAWS........................................................ ..... 89
B-Ix: FORCE COMPONENETS ...................................................... 93
B-X: GOING INTOA SPIN ........................................................... 97
B-XI: DON’T ROCKTHE BOAT ................................................... 100
APPENDIX C: DATA TABLES ................................................................ 103
LITERATURECITED ............................................................................ 105

LIST OF TABLES

Table, l: Rubric for Evaluation Of Fluid Mechanics Question One ........................... 35
Table 2: Rubric for Evaluation of Fluid Mechanics Question Two ........................... 35
Table 3: Rubric for Evaluation of Fluid Mechanics Question Three .......................... 36
Table 4: Rubric for Evaluation of Fluid Mechanics Question F our .......................... 36
Table 5: Rubric for Evaluation of Fluid Mechanics Question Five ........................... 36
Table 6: Rubric for Evaluation of Thermal Energy Question One ............................ 37
Table 7: Rubric for Evaluation ofThermal Energy Question Two............ 37
Table 8: Rubric for Evaluation of Thermal Energy Question Three .......................... 38
Table 9: Rubric for Evaluation of Wave Properties Question One ........................... 38

Table 10: Rubric for Evaluation of Wave Properties Question Two ......................... 38
Table 11: Rubric for Evaluation of Wave Properties Question Three ........................ 39
Table 12: Rubric for Evaluation of Wave Properties Question Four ......................... 39
Table 13: Rubric for Evaluation of Sound Question One ...................................... 39
Table 14: Rubric for Evaluation of Sound Question Two ..................................... 40
Table 15: Rubric for Evaluation of Sound Question Three .................................... 40
Table 16: Rubric for Evaluation of Reflection Question One ................................. 40

Table 17: Rubric for Evaluation of Reflection Question Two ................................. 41
Table 18: Rubric for Evaluation Of Reflection Question Three .............................. .41
Table 19: Rubric for Evaluation of Electrostatics Question One ............................. 42

Table 20: Rubric for Evaluation of Electrostatics Question Two ............................. 42
Table 21: Rubric for Evaluation of Electrostatics Question Three ............................ 42

vi

Table 22:
Table 23:
Table 24:
Table 25:
Table 26:
Table 27:
Table 28:
Table 29:
Table 30:
Table 31:
Table 32:
Table 33:
Table 34:
Table 35:
Table 36:
Table 37:
Table 38:

Table 39:

Rubric for Evaluation of DC Circuits Question One ............................... 43

Rubric for Evaluation of DC Circuits Question Two ............................... 43
Rubric for Evaluation of DC Circuits Question Three ............................. 43
Rubric for Evaluation of Newton’s Laws Question One ........................... 44
Rubric for Evaluation of Newton’s Laws Question Two ........................... 44
Rubric for Evaluation of Force Components Question One ....................... 45
Rubric for Evaluation of Force Components Question Two ....................... 45
Rubric for Evaluation of Circular Motion Question One .......................... 45
Rubric for Evaluation Of Circular Motion Question Two .......................... 46
Rubric for Evaluation of Rotational Motion Question One: ...................... 46
Rubric for Evaluation Of Rotational Motion Question Two ........................ 46
Rubric for Evaluation of Semester One Exam Question One ..................... 47
Rubric for Evaluation of Semester One Exam Question Two ..................... 47
Rubric for Evaluation Of Semester One Exam Question Three .................... 47
Rubric for Evaluation Of Semester One Exam Question Four .................... 48
Comparison of Pretest and Postest Data by Topic ................................. 111
Semester End Comparison for Target Questions ................................... 111
Comparison of Posttest Scores for Observers and Presenters ................... 112

vii

LIST OF FIGURES

Figure 1: Comparison of Pretest and Posttest Scores .......................................... 20
Figure 2: Semester End Comparisons for Target Questions .................................. 26
Figure 3: Comparison of Posttest Scores for Presenters and Observers ...................... 27
Figure 4: Responses to the Student Opinion Survey ............................................ 28
Figure 5: Ventmi’s Principle Question ............................................................ 35
Figure 6: Reflection of a Concave Mirror Question ........................................... 41
Figure 7: Force Components on an Inclined Plane Question ......................... . ......... 44
Figure 8: Equal Masses in Different Liquids............. ........................................ 52
Figure 9: Pressure Fountain ........................................................................ 54
Figure 10: Air Flow Around a Ball in a Funnel .................................................. 57
Figure 11: AirFlow AroundaBall inanAir Stream ........................................... 57
Figure 12: Heat of Lead and Water ................................................................ 59
Figure 13: Boiling Water in a Paper Cup ......................................................... 61
Figure 14: Ripple Tank62
Figure 15: A Coupled Pendulum ................................................................... 67
Figure 16: Open Tube Harmonics ................................................................. 68
Figure 17 Closed Tube Harmonics ................................................................. 68
Figure 18: Sound Visualization Demonstration .................................................. 69
Figure 19: Beats...., .................................................................................. 70
Figure 20: The Laser Spirograph .................................................................. 72
Figure 21: The Law of Reflection ................................................................. 73

viii

 

Km 22:
Figure 23:
Figure 24:
Figure 25:
Figure 26:
Figure 27:
Figure 28:
Figure 29:
Figure 30:
Figure 31:
Figure 32:
Figure 33:
Figure 34:
Figure 35:
Figure 36:
Figure 37:
Figure 38:

Figure 39:

Reflection on a Concave Mirror ...................................................... 73
Reflection on Two Surfaces .......................................................... 74
The Van deGraff Generator ........................................................... 76
Induced Charge .......................................................................... 77
Franklin’s Bell .......................................................................... 79
Conduction and Induction in Franklin’s Bell ....................................... 79
Spring Cymbals ......................................................................... 80
Ohm’s Law Demonstration ........................................................... 83
Resistors in Series ...................................................................... 84
Resistors in Parallel .................................................................... 84 .
Compound Circuit ...................................................................... 85
Inertia Of a Book ........................................................................ 89
Hanging Spring Scales ................................................................. 90
Returning Can ........................................................................... 9O
Force Components on an Inclined Plane ............................................. 94
Rocking Candle ....................................................................... 100
Forces on Ruler and Hammer ....................................................... 101
Torques on the Ruler ................................................................. 101

ix

 

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I. Introduction

One tool used by science educators in the teaching of science concepts is the
classroom demonstration. Many teachers can recall a time in their own education when a
well-performed demonstration sparked their interest; thus, they wish to light that spark in
others in the same way. A demonstration can capture the attention of a class and focus it
on a single point: the description and explanation of what was just observed. For that
matter, practicing science teachers still like to see a good demonstration. Personal
observations at science teacher conferences Show the sessions that are presenting
demonstrations are always well attended, while those covering educational philosophy
are less popular. Many of the teachers at the demonstration sessions are looking for
unique ways to demonstrate a concept, while others simply appreciate good
demonstrations and are there to observe and learn themselves.

The collection of anecdotal evidence in support of classroom demonstrations is
impressive. Moreover, the journal Physics Teacher published a collection of five papers
on the subject of classroom demonstrations (F rier, p. 384; Pinkston, p. 387; Hilton, p.
389; Carpenter and Minnix, p. 391; Johnston, p. 393). Virginia Military Institute physics
professors Rae Carpenter and Richard Minnix express the collective opinion of these
papers:

“A good lecture demonstration seems to whet the appetite of young
students. Some even stay around after class to discuss what they saw and

to try it for themselves. Moreover, the students themselves believe the

demonstrations are valuable. An overwhelming majority of our student

course evaluations show that they feel the lecture demonstrations increase

their understanding and that the time devoted to them is well spent.” (392)

Based on personal experience and conversations with other teachers there is little doubt

that lecture demonstrations are popular with students. It is not uncommon after the

completion of a demonstration for students to request to see it again. This generally
cannot be said for the derivation of a mathematical formula.

Over time, great physicists have used clever demonstrations to illustrate their
subjects. It is rumored that Michael Faraday, when lecturing, would have forty or more
demonstrations to perform in a single lecture. The response was overwhelming. His
lectures were typically standing room only with most of the attendants not even students
in the class (Sixtus, 1993). Hans Christian Oerstead made his famous discovery of
electromagnetism during a lecture demonstration. Recognizing the importance of
demonstrations, Oerstead is quoted as saying, “The mere dry lectures as were given in
Berlin without the art of experimentation do not please me, for after all, all scientific
advances must start from experimentation.” (Hilton, 1981).

In modern times it is hard to imagine a single demonstration that had more
impact on the public than that of physicist Richard Feynmen during the investigation
into the 1986 explosion of the space shuttle, Challenger. A major debate was brewing
on the subject of the shuttle’s O-rings. Some believed that the O—rings lost flexibility at
low temperatures, causing the fuel to mix too quickly which lead to the shuttle’s
explosion. The manufacturer of the O-rings insisted that they were still very flexible at
low temperatures and were not the problem. Before a congressional hearing, the Nobel
Prize laureate used a pitcher of ice water and a c-clamp to demonstrate how the shuttle’s
O-rings lostthpir flexibility at low temperatures causing the fuel leak that led to the
disaster. (Feynman, 198 8) This story shows the power of a demonstration. The
commission members no longer had to hear testimony on this point. They had seen the

results with theirpwn eyes.

All demonstrations, however, are not equal. Just as a poor laboratory activity can
amount to nothing more than a craft project, a poor demonstration can be nothing more
than a magic triclc The difference between a magic trick and a science demonstration is
that a magician keeps the secrets to himself, while a science teacher’s goal is for
everyone to discover the secret, and through that discovery learn a science topic. Were
the people who packed Faraday’s lecture hall interested in learning new and exciting
things about physics, or were they there to watch a Show? The importance of balancing
Showmanship and content is well described by Nanuet High School physics teacher John
Johnson.

“First, the demonstration must educate, but if it also entertains, SO

be it. You always want impact; you want the concept to be remembered.

I see nothing wrong in staging and presenting as many demonstrations as

possible in a dramatic and theatrical way, as long as it doesn’t detract from

the physics being taught. Anything well displayed is half sold. And we

are selling ideas and competing with every other discipline.” (Johnson,

1981)

Of course demonstrations must be engaging and even entertaining to a point. The
mastery of science concepts requires a good deal of effort on the part of the student.
Students must be enticed to put forth the effort and sustain the effort until mastery is
reached. (Anderson and Okhee, 1997) The entertainment value of demonstrations can
serve the purpose of the “bait” needed to lure the students to focus their attention and
efforts long enough to master a concept.

Not only do personal anecdotes support the use of demonstrations during class
lectures, but there also exists quantitative data to support this idea. During the 1980’s,

F.D. Boulanger compiled data from over fifty independent studies over a fifteen-year

period on effective methods of science education. Through this meta-analysis, Boulanger

was able to note several important principles related to student outcomes (in Hofwolt,
1989). One such principle had to do with the greater ability of students to understand
material that is presented in a less abstract manner:

Instructional materials may be placed on a continuum from
concrete to symbolic: manipulatives are more concrete than are pictorial
stimuli, which in turn are more concrete than printed text material.
Similarly, a student’s lab experiment is more concrete than is a teacher’s
demonstration, and the teacher demonstration is more concrete than a
lecture. All the studies Boulanger looked at showed that greater realism or
concreteness in supporting instructional materials led to greater cognitive
achievement (Hofwolt, 1989).

Being more concrete than a lecture, a demonstration illustrates a topic much more
effectively than a verbal description alone.

It is worth noting that the study referenced above states that a laboratory
experiment is more concrete and consequently more effective than are lecture
demonstrations. The enthusiastic support in this paper for classroom demonstrations
should not be interpreted as a suggestion that they should replace the legitimate role of
hands-on lab activities in a science curriculum. In fact, the Boulanger study lists hands-
on activities as one of the six instruction clusters that have the most significant effects on
student outcomes (Hofwolt 1989).

There are, however, certain advantages that demonstrations have over laboratory
experiments. A typical demonstration requires much less class time than does an
experiment. Demonstrations only require one set of lab equipment to perform it for a
large group and can be very appropriate when the required equipment is expensive. Most

demonstrations only work well after they are practiced by the presenter or lose their

effectiveness if there is no surprise for the observer.

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One clever demonstration on the index of refraction counts on the surprise factor.
A Pyrex glass test tube is placed in Wesson oil before it is shown to the class. Pyrex
glass and Wesson Oil have the same indices Of refraction so the test tube cannot be seen
in the oil. The presenter announces that he has discovered that Wesson oil fixes broken
glass. He produced a test tube, smashes it to bits with a hammer and places the pieces in
the beaker of Oil. After stirring and allowing the suspense to build, the presenter reaches
in with a pair of tongs and to the surprise of the class, removes the solid test tube that is
hidden in plain sight. An experienced demonstrator will have a second test tube in the
beaker of Oil ready to go, because the class will want to see it done again. (Ewing, 2000)
This demonstration could not be done as a lab experiment. The students would know that
the intact test tube was in the Oil and thus there would be no surprise and very little effect.

With the consensus of opinion being that demonstrations are beneficial, it is
curious why more of them are not done. The reasons for not doing demonstrations are
mostly logistical. Demonstrations take time to set up and practice. With accumulating
materials, assembly and practice, a good demonstration can require a few hours of
preparation. With the other burdens of teaching, a few hours of preparation for fifteen to
twenty minutes of class time is a very extravagant use of the teacher’s time. The problem
is well stated in the following review of a book of physics demonstrations.

“The effective demonstrator must spend hours searching the literature for

good ideas; he must also devote time, skill and patience in putting things

together and rehearsing over and over again to make sure that no vital

matter has been overlooked. It is a small wonder that many teachers . . .

have found it simpler to confine their demonstrations to drawings, charts

and equations on the blackboard, instead of trying to show the class how
things really go.” (Pinkston 1981)

Considering the preparation requirements, the question changes fiom “Why
aren’t more demonstrations done?” to “Why are any done at all?” Major universities,
recognizing the importance of demonstrations, hire staff for the sole purpose of preparing
and sometimes even performing demonstrations, thus relieving the professor from these
duties. This, however, is not true for high schools. Any demonstrations to be done must
be prepared and performed by the classroom teacher.

Alternatives to physical demonstrations do exist. In large demonstration sessions
at science teacher conferences, it is not uncommon to see teachers carrying video cameras
to record the demonstrations and play them back for their own class. Similarly,
collections of well-performed demonstrations on video are available to purchase from
science supply companies, such as Sargent-Welch and Arbor Scientific. These
collections do have certain logistical advantages to live demonstrations, but it is hard to
believe that they could be as effective as seeing the demonstration live. University of
Minnesota physics professor George F rier likens the use of demonstrations on film to that
of seeing pictures of a friend’s children. Actually meeting the children is required to get
to know them. (Frier, 1981)

The challenge for a high school science teacher is to incorporate meaningful
demonstrations into his class while still managing other professional responsibilities.
Some teachers have found it appropriate to use students as presenters of science
information to other students. In one example of this, the high school physics class at
Lawrence Central High School in Indianapolis, Indiana presented a “Physics Road Show”
to elementary classes in their district. This physics class prepared demonstrations in

several topic areas. While no quantitative data on the effectiveness of this program was

reported, the anecdotal evidence was encouraging. It claimed benefits for both Observers
and presenters. (Edelman and Goeglein, 1995) A similar example involved a physical
science class at Omaha South High School in Omaha, Nebraska. This class began by
showing demonstrations for special education classes in the high school building. The
program has since expanded to include presentations to elementary classes and in a local
science museum. As with the previous example, there was no quantitative data, but
anecdotal evidence was very supportive of the approach. (Galus, 2000)

In another example of students as presenters, middle school teacher Daniel
Mennelly set up an enrichment program with a structure he calls a “pyramid scheme”. In
this format, he targeted a small group of students to prepare an enrichment lab activity.
These students then helped others through the activity. The resulting data are also
anecdotal with the effort considered to be a success. (Mennelly, 2000) In all of these
examples, students successfully presented science information to other students. It was
asserted in each case that the effort was beneficial for both the presenter and the observer.
This research project further explores the effectiveness of using students as classroom

presenters.

11. Implementation

This research project was undertaken to find and evaluate an effective way to
incorporate more physical demonstrations into a high school physics class at Mio
AuSable High School in Mio, Michigan. This project was implemented during the 2001-
2002 school year. Mio is a small, rural community in northeast Michigan. The school
contains grades K-12 all in the same building with a total student count near 900. In a
small school, each teacher must wear many hats and consequently preparation time is a
rare commodity. The course in this study was a year-long high school physics class. It is
intended for seniors who have taken or are taking trigonometry. The course already had
many laboratory experiments and improvements in this area were not needed. However,
very few demonstrations were done. It was the teacher’s desire to increase the overall
number of demonstrations prepared in such a way that they could be done easily every
year.

The idea was to have groups of students prepare and perform the demonstrations
for the rest of the class. The students would collect the materials, assemble the
equipment, study and master background information, practice the demonstration and
present it to the rest of the class. The rationale for this approach is that time needed to
prepare the demonstration would be provided by the group of students and not by the
teacher. On the surface, it may seem that this approach treats the students of the physics
class as mere assistants, requiring them to make class preparations that could easily fall
under the teacher’s duties. However, preparing a demonstration is not like making
copies, carrying the teacher’s books or washing his car. The students performing the

demonstration stand to gain from their independent, in-depth study of a physics topic.

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The class in which this approach was implemented and documented was made up
of nineteen students, ten males and nine females. All nineteen students were Caucasian,
and all had completed the minimum two classes in science required for graduation and
were taking the physics class as an elective. This was a particularly large physics class
for Mio AuSable High School. A typical physics class would have 6-10 students. NO
data was collected on the economic background of the students’ families, but it is
believed that it is a mixture of low to upper middle class family incomes. Being from a
small community, the students knew each other quite well, most being in classes together
since early elementary grades. Finally, for no other reason than to help the reader
appreciate the flavor of the class, it is worth noting that the class contained two sets of
twins. It is not believed that these family relationships affected the study, but they did
make the class more colorful.

In the design of the student-led demonstrations three factors were considered.
First, the demonstrations had to be sufficiently interesting to make it worthy of the
student group’s effort to prepare and present it. Second, the descriptions of the
demonstrations had to be clear enough that a group of students could read them and,
based on the reading, prepare the demonstration with little or no help from the teacher.
Third, the descriptions had to contain sufficient background information that the student
presenters would be able to adequately describe the scientific principles behind their
demonstrations.

Picking good demonstrations for the students to prepare and present was the first
hurdle to cross. Many of these required special equipment that the rest of the class did

not have access to or provided a surprise ending. During the Summer of 2001 physics

demonstrations were collected and developed. Most of the demonstration ideas came
from books, intemet web sites and discussions with other science teachers. Other
demonstrations were those that have been performed in physics classes for years and not
attributable to a single source. For each Of these demonstrations, a written description
was prepared so that a student group could prepare the demonstration with little help
from the teacher. Appendix A is a complete description of the demonstrations from the
eleven topic areas discussed in this paper.

When each topic was introduced, one group was given a written description on
how to prepare and perform the related demonstration or group of demonstrations and a
deadline when they would need to perform it for the class. The groups were instructed
that every member of the group had to work on every part of the demonstration. It would
not be acceptable for one student to handle the materials, a second student to organize the
demonstration and a third student to present it. Students read the instructions and
prepared the demonstration independently for the most part, seeking out the teacher’s
help only when they had a particular question.

Finally, the students needed to acquire sufficient background information to be
able to adequately describe the scientific principles demonstrated. As was stated
previously, it is easy for a demonstration to turn into nothing more than a magic trick. If
the presenters have little idea about what is going on, then the point of the demonstration
is nearly lost from the start. According to the Third International Math and Science
Study (T IMSS) the quality of science instruction is directly related to the level of

understanding of the presenter. (Schmidt and Wang, 1999)

10

This point presents a particular problem for this project. The students take the
class because they do not know the subject. The students build their background
knowledge through reading supplemental material, participating in class and through the
experience of preparing the demonstration itself. Along with each set of demonstration
instructions, a written description of the scientific principles being taught was included
for the presenters to read. Also, the students were participating in class concurrent with
preparing their demonstration. Generally, the demonstration was performed near the end
of a unit. This gave the presenters a chance to learn with their peers before making the
presentation.

While most groups approached the demonstrations with a great deal of
enthusiasm and a desire to present them well, certain precautions were made by the
teacher to ensure that the presenters understood their material. During the first semester,
homework questions particularly developed for the project were identified to the student
presenters as covering the topics being described in the demonstrations. While these
questions were assigned to all students, they were worth more points for the presenters
than for the other students in the class. The added importance Of these questions gave the
presenters the extra incentive to get them correct thus showing that they had mastered the
material. Examples Of these homework questions can be found in Appendix A-II.

Student homework assignments in this course including those used for the
purpose of evaluating the student-presenters’ knowledge were computer generated using
the LON-CAPA software system developed in the Laboratory for Instructional
Technology in Education at Michigan State University. While this system has many

potential applications, in this course it was used exclusively for generating and managing

11

homework assignments. This system randomly generates elements of a homework
assignment and provides an individual version for each student. For numeric problems,
the system randomly generates numbers from a given range. Conceptual questions are in
the form Of true/false, fill in the blank, matching or selecting from Options (greater
than/less than, increase/decrease. . .). Conceptual questions are randomized by selecting
some questions from a group of possible questions and by changing the order that the
questions are presented. Examples of these homework questions can be found in
Appendix A of this paper.

Students submit their answers via the intemet. The system evaluates the answers
and gives immediate feedback to the students. A student who gets an answer wrong can
be given the chance to correct it. The teacher has the option to set the number of times
that students may submit answers and the weight Of each question. The teacher can also
set tolerances to specify how close the answer must be to the computer’s answer and the
number of significant figures that are acceptable in the answer. One drawback of the
system is the inability to assign short answer or essay questions to the students. There is
no way for the system to evaluate such a question. Students were asked this type of
question on laboratory assignments and on tests so that the teacher could grade them.

At the beginning of a topic, each student was given an individualized problem set
to complete during the unit. The assignment was usually due near the end of the unit.
During long units the problem set would be divided into two parts with one part due near
the midpoint of the unit. While some students would wait until the end to work on the
assignment, others would work on it steadily through the unit. As students encountered

problems they discussed them with the teacher or with other students. Because of the

12

individual nature of the assignments, students could discuss how a problem was done
without simply being given the answer.

In the second semester, the presenters were required to submit to the teacher
written observations and explanations from their demonstration. The written work had
three elements for each demonstration: 1) a prediction about what would happen during
the procedure, 2) a description of what actually happened during the procedure, and 3) an
explanation of the physical basis for the observations. During the second semester
demonstrations, the Observers wrote about the demonstration in the same way. This
change was made to align the activity of the presenters with the activity of the observers,
which was changed during the second semester also. This change is explained later in
this section.

The final guarantee that the material was being presented correctly was the
classroom teacher. As always, it is the teacher’s responsibility to ensure that the material
being presented is correct and well explained. As the students presented their
demonstration, the teacher was alert to inaccuracies and unclear descriptions. When they
occurred, the teacher would have the group provide a correct explanation. If the review
was insufficient, then the teacher would explain the point to the class so that both the
presenters and the observers would understand it. In actual practice, it was not
uncommon for the teacher to ask a group to explain a concept again, but rare that the
second explanation was inadequate.

Based on observations and research during the first semester, the procedure for
presenting the demonstrations was changed for the second semester to include a more

active role on the part of the observers. During each demonstration, the students

13

observing the demonstration were required to make predictions, record observations and
explain those observations in writing. This technique of immediately assessing student
understanding of a demonstration was used in the Chemistry Department at Louisiana
Technological University as a way to enhance and evaluate critical thinking skills.
(Radford, Ramsey and Deese, 1995) In a study performed at this university, two sections
of a chemistry class were evaluated. In the first section, the demonstrations were
presented to the class, but no immediate feedback from the students was required. In the
second section, the students were immediately assessed on their Observations and
explanations of the demonstrations. Their data showed significantly higher test score for
the second group (Deese, Ramsey Walczyk and Eddy, 2000). This process was added in
the second semester of this course to see if it would increase the observers attention to the
demonstrations and their understanding of the concepts presented.

During the first semester, demonstrations from six topic areas were evaluated:
fluid mechanics, thermal energy, waves, sound, reflection and electrostatics. During the
second semester, demonstrations from an additional five topic areas were evaluated: DC
circuits, Newton’s LaWs, force components, circular motion and rotational motion.

The order of topics is different fi'om that of a traditional physics class. The Mic
Physics class has been organized in this way for several years. It was originally changed
to accommodate the math abilities of the students. Many of the students were taking the
Trigonometry course concurrently with physics. At the beginning of the year, most of
these students were unfamiliar with even basic trigonometry operations involving right

triangles. Moving the mechanics topics to the second semester allowed the students to

14

acquire more background mathematical knowledge, and they were better able to

comprehend the material presented.

Summary of Topics: The following is a brief summary of the topics in the order
that they were presented. A complete description of the demonstrations performed is
found in Appendix B of this document. This is not a comprehensive list of all topics
taught in this introductory physics class, but only those topics for which student-led
demonstrations were evaluated.

Fluid mechanics (Appendix B-I) was the first topic area presented. The student
group demonstrated Archimedes Principle by floating objects of equal mass in different
liquids to show that the density of the liquid affected the volume of liquid displaced. A
small pressure fountain was constructed to demonstrate the flow of fluids over a pressure
gradient and the effects of height on pressure, and balls were made to float in a stream of
air to demonstrate Bernoulli’s Principle.

Thermal energy (Appendix B-II) was the second topic. This group presented a
collection of four different demonstrations illustrating this topic. Thermal expansion was
demonstrated with a brass ball and a ring that was slightly smaller, and boiling water in a
paper cup showed that objects in contact with each other stay at an equal temperature.
The efl’ect of specific heat and heat capacity was shown in two ways. First, the group
presented equal masses of water and small lead pellets at the same temperature. Equal
masses of wax were placed in each. The wax placed in the water melted much more
showing its higher specific heat. Heat capacity was demonstrated by placing equal sized

samples of various metals at the same temperature on a thin sheet of wax. The samples

15

melted through in an order not equal to their specific heats. Through these
demonstrations it was shown that heat capacity depends both on mass and the specific
heat of the material.

Wave Properties (Appendix B—III) was the third topic area demonstrated. For this
topic a ripple tank was used to demonstrate several principles. Waves were generated to
show that they travel along straight-line paths. The frequency of the waves was changed
to Show the inverse relationship between frequency and wavelength. Various objects
were placed in the tank to show the properties of reflection, refiaction and diffraction.
Finally, multiple waves were produced to Show the property of interference.

Sound (Appendix B-IV) was the fourth topic area presented. The group
demonstrated resonance in several ways. They showed a coupled pendulum, they
resonated several open and closed tubes at various frequencies and they used a laser
shining on a vibrating membrane to show how vibrations are dependant on both
frequency and amplitude. Finally, they extended the topic to include the interference of
sormd waves by projecting similar sound waves and demonstrating that their beat
frequency is equal to the difference in frequency between the two sounds.

The reflection of light (Appendix B—V) was the fifth topic area presented. The
group used a laser, mirrors and a fog machine to illustrate the law of reflection. They
reflected the laser beam ofi' a mirror set at various angles and showed that the law applies
to curved mirrors as well. They then combined several of these ideas to construct a laser
Spirograph from two spinning concave mirrors. The device projected circular patterns on

a screen that would change with the rotational speeds of the mirrors. The group then

16

explained how the device worked using the principles of reflection that they had
previously explained.

The final topic area demonstrated in the first semester was electrostatics
(Appendix B—VI). The group prepared several demonstrations using a Van deGraff
generator. They showed spark discharge, how objects are charged by conduction and
induction and the Basic Law of Electrostatics. In the process they built a set of static
controlled symbols and a static bell that was first described by Benjamin Franklin.

The first topic presented in the second semester was DC circuits (Appendix B-
VII). The group constructed resistors out of play dough and assembled them into various
circuits. Through these circuits they compared the distribution of current and voltage in
both series and parallel circuits.

The next topic area presented was Newton’s Laws (Appendix B-VIII). The group
exhibited three demonstrations. In the first, they suspended a mass and showed the
effects of sudden forces and gradual forces on it. Through these demonstrations they
were able to discuss both the first and second laws. During the second demonstration,
they hung a weight from a spring scale and noted its reading. They then showed that
hanging two spring scales linearly did not affect the reading. Both scales read the same
as one scale did supporting the same weight. This showed Newton’s Third law of equal
and opposite forces. The third demonstration also demonstrated the third law by rolling a
coffee can containing a counter weight across the floor. The can will roll a certain
distance and then return. The observers, not being aware of the counterweight, would see
the can’s behavior violating the first law, but when the counterweight was revealed, the

third law was again reinforced.

l7

Force components (Appendix B-IX) was the third topic area of this semester. The
group compared parallel forces and normal forces using a toy car propped on an inclined
plane. Weights were suspended from pulleys to balance the normal force and the parallel
force. The board making the inclined plane was then removed, showing that it was no
longer necessary to keep the car inclined as it was on the ramp.

The fourth topic area of this semester was circular motion (Appendix B-X). This
group carried out two demonstrations. The first showed that objects can have different
tangential speeds even if their angular speeds are identical. This was demonstrated by
one person swinging two tennis balls on different length strings. The swings were such
that each ball had the same rotational period. When they were released, the ball with the
longer string traveled farther showing it had a larger tangential speed. The second
demonstration showed that objects can travel in a vertical circle once they reach a
sufficient speed by swinging a bucket of water in a vertical circle. These demonstrations
were both performed outside.

The final topic area was rotational motion (Appendix B-XI). This group also
presented two demonstrations. The first showed a balanced candle burning at both ends.
As the candle burns, the center of mass shifis slightly causing the candle to rock back and
forth. The second demonstration set up a hammer suspended in a way that seemed to
defy gravity. The group then used this setup to Show how the balance of forces and
balance of torques keeps the system in equilibrium.

The effectiveness of the demonstrations was evaluated through a series of
questions that were developed for each demonstration. These questions can be formd in

Appendix A-I of this paper. The questions were presented in a pretest at the beginning of

18

the chapter in which the demonstration was to ,be presented. The same questions were
then asked again on the chapter ”posttest. A few selected questions were then asked again
on the first semester exam to determine long-term retention of the information

A scoring rubric was developed for each question, which is also found in
Appendix A-I. The pretest and posttest questions were scored and the data compiled for
each topic area. Average pretest and posttest scores were examined for each chapter to
assess student gains. The data were then disaggregated to compare the performance of
the students presenting during a particular chapter to. that of the rest of the class. An
opinion survey was also given to the class as an indicator of the students’ Opinions about
the impact of classroom demonstrations.

Three students were also identified whose responses on the pretests and posttests
would be looked at in more detail. Their individual responses to selected pretest and
posttest questions were collected and will be presented in the results section of this paper.

The students selected had varying abilities to show how this project impacted students at

varying levels.

19

Percent Correct

III. Results

The effectiveness of student-led physics demonstrations was evaluated in several
ways. Pretest and posttest data were examined for each topic area both for the class as a
whole and comparing observers to presenters. A few topics were evaluated for long-term
retention. Actual responses from three different students of varying ability were closely
examined. Finally, an opinion survey was used to see student opinions on the
effectiveness of student-led demonstrations.

In each of the eleven topic areas, students scored considerably higher on the
posttest than the pretest. The results for each topic area are found in Table 37, which is
located in Appendix C of this paper. They are summarized graphically in Figure 1.

Figure 1: Comparison of Pretest and Posttest Scores

 

 

 

 

100
90..77272i77i7777#-7 7‘7i7 7A
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70—» e , we 7. ,, e e—e
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agebse-eeeww‘e
ééee’éefgf as:figjoes;3:0,ofyeé’1siyc’
as?" «of .1fo 9} 9" tip at" 00° I
3° Q‘ n=l9
Topic
I I Pretest I Posttest l

 

The average improvement was 62.5 percentage points above the pretest. The
topic that showed the greatest improvement was electrostatics, which had an
improvement of 80.6 percentage points over the pretest. The area that showed the least
improvement was force components, which had only an improvement of 39.2 percentage
points over the pretest. It is noted that the lack of improvement in this topic area is a
result of high performance on the pretest and not a poor performance on the posttest.

The improvement between the pretests and posttests is also evident through
individual student responses. Three students’ responses will be examined. The three
students will be referred to as Student A, Student B and Student C. Student A was a
female who maintained an A average throughout the year. She had a cumulative grade
point average of 4.00. Student B was a male who maintained a B average throughout the
year. His cumulative grade point average was 3.47. Student C was a male who
maintained a C-/D+ average throughout the year. He had a cumulative grade point
average of 2.90.

The first question examined was asked during the section on buoyancy. The
specific question was, “Using Archimedes’ Principle, explain why some objects sink and
some Objects float.” On the pretest, Student A answered “I don’t know what
Archimedes’ principle is, but objects that are less dense than water float, and objects that
are more dense than water sink.” She received 0 points for this response as it did not
discuss buoyancy. She had some understanding on the topic as it relates to density, but
could not explain why an Object with a lower density will float. Students B and C both

left this question blank on the pretest.

21

On the posttest, student A answered the question, “An object will float if the
weight of the Object and the water it displaces is equal to the buoyant force Of the fluid.
A buoyant force is an upward force from the fluid that goes against gravity.” After the
demonstrations, this student knew that Archimedes’ Principle was related to buoyancy
and could define a buoyant force. She did have problems explaining how the buoyant
force is caused and how that affects an object’s ability to float. This answer was scored
for one point.

On the posttest, student B answered, “Buoyant Force equals the weight of the
displaced fluid. When an Object floats that means that the buoyant force that is pushing
upwards is greater than the weight of the object. When something sinks, the buoyant
force is less than the weight.” This student knew that Archimedes’ Principle is related to
buoyancy. He could state the principle clearly and was able to describe why Objects sink
and float. This answer was scored for two points.

Student C answered, “An Object will float if its buoyant force is equal to or
greater than its weight. If its buoyant force is less than its weight it will sink.” This
student demonstrated that he now knew how a buoyant force must compare to an object’s
weight for it to float. He however did not explain how a buoyant force is produced or
what determines its magnitude. This answer was scored for one point.

All three of the students showed improvement over their pretest responses. In
their responses they related buoyant forces to the object’s ability to float and two of the
responses attempted to relate the buoyant force to the displacement of fluid.

During the section on thermal energy, the students were presented with the

question, “You are beating a pan of water on the stove; does the pan get hotter than the

22

water, stay cooler than the water or stay the same temperature as the water? Explain your
answer.” On the pretest, student A answered the question, “The pan does get hot, but not
as hot as the water because the water heats up faster at lower temperatures than the metal
the pot is made of.” Student B answered, “same temp.” Student C answered, “hotter than
the water — the pan is absorbing the heat”. The answer for student B was scored for one
point, while the answers from students A and C were scored for zero points. All three
answers indicated little understanding on this topic.

On the posttest, student A answered, “The pan and the water are at the same
temperature. Since they are in contact the pan, which has a lower specific heat, will
continuously give the water heat energy to reach equilibrium.” Student B answered,
“The temp of the pan and water stay the same because since they are touching each other,
they absorb the same amount of heat.” Each answer correctly identifies the two materials
as being at the same temperature, but incorrectly identifies why they are at the same
temperature. Student A identifies specific heat as the factor that determines the direction
of energy flow while student B relates it to the absorption of heat energy. Each was
scored for one point. Student C answered, “They are at the same temperature. As the pan
gets hotter the water absorbs the heat causing them to be the same.” He identifies the
materials as being at the Me temperature and states that the heat flows from the pan to
the water keeping them at the same temperature. While this answer could have been
more specific, it was scored for two points.

Again these answers indicate an increase in student understanding. Not only are

the scores higher on the posttest, but also the descriptions include more information

23

 

 

 

indicating that the students are not guessing, but have knowledge on which to base their
answers.

During the section on sound, the students were asked the question, “How do
sound waves vibrate in a tube closed at one end (such as a pop bottle) compared to a tube
open at both ends (such as a trombone)? On the pretest, student A answered, “In the
trombone the vibrations are consistent & uniform as they travel out, but in the pop bottle
the vibrations are uneven because they hit the closed end.” Student B answered, “The
sound waves reflect off the end of the pop bottle and are muffled. The trombone sormd
waves are very loud.” Student C left the question blank. None of these answers indicate
an understanding of how waves resonate in a confined space. All three were scored zero
points.

The posttest showed a considerable increase in understanding for all three
students. Student A answered, “A closed tube vibrates at odd harmonics and a node is at
the closed end and an antinode is at the open end, whereas a open tube vibrates at even
harmonics and an antinode is present at both ends.” Student B answered, “In closed
tubes there is an antinode at one end and a node at the other. In open tubes there is an
antinode at both ends of the tube.” Student C answered, “There is a node at the bottom of
the closed tube. Both ends of the open tube are antinodes with a node in the middle
causing the vibrations to be different.” All three responses show an understanding of the
location of nodes and antinodes for a standing sound wave. Also, all three correctly
describe the differences between the two types of tubes. Each answer was scored for two

points.

24

Each of these examples shows student improvement in the topic areas covered by
the demonstrations. This is true across all eleven of the topic areas evaluated in this
paper. It is also worth noting that the highest achieving students did not always give the
best answers. In the examples shown above, Student A was more likely to attempt an
answer on the pretest, although it ofien was not right. She was no more likely to get a
correct answer on the posttest than were students B and C. It was anecdotally noted
during the class that overall performance was not necessarily related to success on the
demonstration related questions. While some upper level students were very interested in
the demonstrations, others did not seem to relate well to them. Some lower achieving
students seemed quite interested in the demonstrations and therefore performed equally
well.

At the end of the first semester, four topics, Archimedes’ principle, specific heat,
wave properties and the frequency-wavelength relationship, were revisited to measure
long term retention of the information covered. Each topic was covered nine to fifieen
weeks before the semester end. On the semester exam, the students were asked the same
questions as were asked on the pretest and chapter test. The questions are found in
Appendix A-I. The results are listed in table 38,- which is found in Appendix C of this
paper. The results are also summarized graphically in Figure 2. As is shown, students
were able to recall information on the selected topics at the end of the semester. Student
performance in the four topics measured was considerably higher than for the respective
pretest question. Students performed comparably to the posttest in each area. In two

areas students performed even higher on the semester exam than on the chapter posttest.

25

Figure 2: Semester End Comparisons for Target Questions

Percent Correct

 

archimedes' principle specific heat wavelength- wave properties
Topic fiequency '

I Pretest I Posttest I Semester EndJ

 

 

Data was also collected for each topic comparing the performance of the students
presenting during that topic to the students who only observed during that topic. This
data is reported in Table 39, which is found in Appendix C of this paper and summarized
graphically in Figure 3.

As Figure 3 illustrates, the demonstrators outperformed the observers in ten of the
eleven topic areas. The greatest disparity between presenters and observers occurred
during the demonstrations on wave properties where the demonstrators exceeded the
observers by 14.5 percentage points. For the fluid mechanics demonstrations, the
demonstrators and observers are essentially equal, and during the demonstrations on
rotational motion, the observers outperformed the presenters by 2.5 percentage points.

The presenters outperformed the observers an average of 6.5 percentage points.

26

Figure 3: Comparison ofPosttest Scores for Presenters and Observers

 

 

Percent Correct

 

 

 

 

- x?
it so \ at o _ e -o° v
Q‘ @960 A” Q $6 0&0 0‘6) <§95?“
Topics n = 19
I Demonstrator Posttest I Observer Posttest J

 

The presenters perform modestly better than the observers, but the difference is
not overwhelming. The relevance comes from the consistency at which the
demonstrators outperformed the observers. This indicates that preparing and performing
the demonstration consistently may give the presenters a slight advantage over observers.
In the second semester, the requirements of the observers were changed in an attempt to
improve observer scores. There is little difference between the scores of the first
semester and the second semester to indicate that the change was efi‘ective.

The final evaluation instrument was a student opinion survey, which is found in

Appendix A-III. The survey asked students to rank a statement with a number ranging

27

Figure 4: Responses to the Student Opinion Survey

‘Wmdmgdammmflfimnhdmflnnkmnflmnnmmd

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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8 H)
§5
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28

fiom one to five. Five indicated that the student strongly agreed with the statement, one
indicated that the student strongly disagreed with the statement, and three indicated that
the student neither agreed nor disagreed with the statement. The responses to. four
selected questions are graphically illustrated in Figure 4. The responses indicate that
students feel that the demonstrations did help them learn. ' They agreed with this
statement both as observers and as presenters with a four being the most common
response to each question.

Survey questions were also asked about how the students enjoyed preparing and
presenting the demonstrations. For each of these questions, the most common response
was a three. This means that the students neither liked nor disliked it. The responses
were slightly more positive for preparing the demonstrations than for presenting the
demonstrations to the class. The student surveys do reflect a healthy attitude towards the
project. The students could see the benefits of what they were doing, even if presenting

the demonstrations was not a favorite thing to do.

29

. IV. Discussion

In the Introduction to this paper anecdotal evidence was presented that indicated
demonstrations are an important tool for teaching science. An evaluation of the physics
curriculum at Mio AuSable High School showed few demonstrations being done by the
instructor due to a lack of time for their preparations. It was the desire of the instructor
that the number of demonstrations be increased and structured in such a way that they
could be repeated every year. During the summer of 2001, a set of demonstrations was
developed, during a designated research time at Michigan State University, that could be
prepared and presented by groups of students to the rest Of the physics class. The
purpose of this project was to evaluate the effectiveness of these student-led
demonstrations.

The results show the demonstrations to be quite effective. Students performed an
average of 62.5 percentage points higher on the posttests than on the pretests. Of course
the gains cannot be exclusively attributed to the demonstrations. The students were in a
high school physics class and most of the topics covered in the demonstrations were
covered in other ways as well. There was not a group of similar students in a similar high
school physics class, but not seeing student-led demonstrations, to serve as a control
group. However, the students did Show significant improvement that at least in part was
related to the demonstrations.

In this project, the students did the work of setting up and presenting the
demonstrations. The implementation section of this paper raised the question of whether
it was fair to the students to require them to make these preparations. It could be asked

what did the students gain from the extra effort. There were two benefits to the students

30

who performed the demonstrations. The first is that physics demonstrations were
performed in their physics class. Few demonstrations were performed in the past due to
lack of preparation time, and this was not likely to change. Without this approach, there
would have likely been very few demonstrations performed during the 2001-2002 school
year. Since the evidence indicates that demonstrations increase the students’ ability to
answer questions on the topics, the effort improves their experience and can therefore be
justified. .

A second benefit "is the students performing demonstrations generally performed
better on the posttest than did the observers. If the classroom teacher performed all of the
demonstrations, no students would get this added benefit. Unlike the total gains of the
class over the pretest, the improved performance of the presenters over the Observers can
confidently be attributed to their preparing and performing the demonstrations. The two
groups had essentially the same experience in the classroom. They sat through the same
lectures, completed the same assignments and conducted the same laboratory
experiments. The only part that was different between the two groups was the
demonstrations. One group prepared and presented them, the other simply observed.
Preparing and performing demonstrations is beneficial to students and is a legitimate
method of having demonstrations presented to a class.

The greatest drawback to the student—led demonstrations was their timing. The
demonstrations were usually performed near the end of the time covering a topic, shortly
before the test. This proved necessary because it took the student-groups time to master
the material and prepare the demonstrations. Sometimes the students needed to try the

procedure several times to be able to perform the demonstrations successfully. The

31

demonstrations may have been more effective earlier in the unit when the topics were
first introduced to the students, but that was not possible.

At the beginning of the second semester 3 change was made in the procedure
followed by the students observing the demonstrations. The observers were given a
response form to fill out during the demonstration. The data collected for the second
semester does not support any conclusions about the effectiveness of this change. The
data is similar between the two semesters, but as the topics covered were different,
comparing the two semesters is not conclusive. Anecdotally, the instructor noted the
observers to be more engaged during the second semester when immediate feedback was
required of them. As the demonstrations continue in future years, it is the intention of the
instructor to require immediate feedback from the students during each semester.

In the Introduction to this paper, it is stated that a prime reason that
demonstrations are not done in high school physics classes is the time needed for them to
be set up. It is worth noting that there was considerable time spent by the teacher getting
the demonstrations prepared to a point that the students could do them successfully.
Would it have been more time effective for the teacher to have prepared and presented
the demonstrations himself? The answer is no, the student-led demonstrations seemed a
better use of the teacher’s time. Most of the work required of the teacher was completed
during the summer when preparation time is more abundant. During the school year,
very little Of the teacher’s time was needed to help the students prepare. Furthermore, the
majority of the teacher’s preparation time in the summer was spent creating written
directions and backgrormd information for students. This is work that will not need to be

repeated in future years. The time investment spent in the summer Of 2001 can result in

32

physics demonstrations performed for many years in the physics class with little time
required of the teacher.

Using students to perform physics demonstrations may not be as time effective for
larger schools. Based on its athletic team divisions, Mio AuSable High School is smaller
than almost 75% Of the schools in the state of Michigan. In a large school, a physics
teacher would likely have several sections of the class. Teacher time spent preparing a
demonstration could be justified by the fact that the demonstration would be shown
several times throughout the day. Furthermore, in a large school, using students to
perform demonstrations would .mean that at any one time several groups Of students
would be preparing a demonstration. This would require more equipment and more
teacher time assisting students. However, for a small school with one section Of physics,
student-led demonstrations are a bargain. They result in a big return on a modest time
investment.

The most significant change in future years will be to the number of
demonstrations done by the class. It was stated earlier that the 2001-2002 physics class
was exceptionally large for MiO AuSable High School. Even if group size is reduced,
there will still be fewer groups presenting demonstrations. This will allow the instructor
to be more selective about the demonstrations assigned to the students.

In future years it would be worth noting if some demonstrations consistently
provide richer experiences for the presenters. During this study, the groups that
presented the topics of force components, wave properties and reflection performed over
ten percentage points higher on the posttest than did the Observers. In future years, the

scores could be compiled in the same way to see if these topics are particularly

33

advantageous or if the improvement is caused by the abilities of the students.
Conversely, the group that demonstrated the topic of rotational motion did not perform
better than the observers on the posttest. It would be worth noting if this trend continues
as well.

Demonstrations can be a powerful tool in teaching science. A demonstration can
take an abstract idea and make it easy for students to visualize. Demonstrations require
little class time and relatively little equipment to perform. The great limitation to
performing many demonstrations is the time required for their preparation. Having
students prepare and present demonstrations is an effective way to include more

demonstrations. It benefits all of the students, the presenters and the Observers alike.

34

Appendix A: Evaluation Tools
Appendix A-I: Semester One Pretest/Posttest Questions with Evaluation Rubrics
Subject: Fluid Mechanics

A stream of air is flowing through the tube below.

/ \ /—D\—

Figure 5: Venturi’s Principle Question

 

1. For the tube above, which section of the tube- has the air traveling the fastest?

(Explain)

Table 1: Rubric for Evaluation of Fluid Mechanics Question One

 

1 point Response identifies the correct region.

 

 

2 points Response correctly relates diameter Of tube to speed

 

 

2. For the tube above, in which section is the air exerting the most pressure on the sides

of the tube? (Explain)

Table 2: Rubric for Evaluation of Fluid Mechanics Question Two

 

1 point Response identifies the correct region.

 

 

2 points Response relates speed to pressure

 

 

35

 

 

3. When you drink through a straw, what forces the liquid up?

Table 3: Rubric for Evaluation of Fluid Mechanics Question Three

 

 

 

1 point Response states that liquids move fi'om areas of high pressure to areas
Of low pressure
2 points Response includes the identification Of the weight Of the air as the

 

source of the pressure.

 

4. Using density, explain why some Objects sink and some Objects float.

Table 4: Rubric for Evaluation Of Fluid Mechanics Question Four

 

1 point

Response is a partial description Of the answer described below.

 

 

2 points

 

Response states that objects with a lower density float on fluids with a

higher density

 

5. Using Archimedes’ Principle, explain why some Objects sink and some Objects float.

Table 5: Rubric for Evaluation of Fluid Mechanics Question Five

 

 

 

I point Response includes a description of a buoyant force being equal to the
weight of the displaced fluid
2 points Response includes an explanation that the buoyant force equals the

 

weight of the Object for the Object to float.

 

36

 

 

 

Subject: Thermal Energy

1. You have a piece of metal with a hole in it. If the metal is heated, will the hole get

bigger get smaller or stay the same size? Explain your answer.

Table 6: Rubric for Evaluation Of Thermal Energy Question One

 

1 point

Response states that the hole increases in size

 

 

2points

 

Response includes the fact that particles move faster and increase their

separation distance.

 

2. In an experiment, 50 g of copper and 50 g of water are each heated to 90°C. Which of

the two contains more energy? Explain why you chose the one that you did using the

term specific heat in your explanation.

Table 7: Rubric for Evaluation of Thermal Energy Question Two

 

1 point

Response states that the water has more heat energy

 

 

2 points

 

Response correctly relates the above to specific heat

 

3. You are heating a pan of water on the stove; does the pan get hotter than the water,

stay cooler than the water or stay the same temperature as the water? Explain your

answer.

37

 

 

Table
W

2pm

 

 

Subj
l. It

that

Tab

2.‘

3.‘

Table 8: Rubric for Evaluation of Thermal Energy Question Three

 

1 point » Response states that the two will have the same temperature.

 

 

2 points Explanation relates the idea that Objects in contact gain or lose energy

until each has the same temperature.

 

 

Subject: Wave Properties
1. It is a property of waves that they travel in a straight line, if this is true why do waves

that start from a point travel as circles?

Table 9: Rubric for Evaluation of Wave Properties Question One

 

 

 

1 point A partial explanation is given.
2 points Response states that the wave travels in a straight line in every
direction.

 

 

2. What is the relationship between a wave’s fiequency and its wavelength?

Table 10: Rubric for Evaluation of Wave Properties Question Two

 

1 point A partial explanation is given.

 

 

2 points Response identifies the relationship as inverse.

 

 

3. What determines the speed of a wave?

38

 

 

 

Table 11: Rubric for Evaluation of Wave Properties Question Three

 

 

1 point

 

Response identifies the medium as the determining factor.

 

4. What is the difference between the properties of reflection, refiaction and diffraction?

Table 12: Rubric for Evaluation of Wave Properties Question Four

 

 

 

 

 

 

1 point Response includes one property correctly described.

2 points Response includes two properties correctly described.

3 points Response includes all three properties correctly identified.
Topic: Sormd

1. Describe what happens to an object to cause it to resonate.

Table 13: Rubric for Evaluation Of Sound Question One

 

1 point

A partial explanation is given.

 

 

2 points

 

Response includes a description of a standing sound wave.

 

2. How does sound waves vibrate in a tube closed at one end (such as a pop bottle)

compared to a tube open at both ends (such as a trombone)?

39

 

 

 

Table 14: Rubric for Evaluation of Sound Question Two

 

1 point

A partial explanation is given.

 

 

2 points

 

Response distinguishes between the positions of nodes and antinodes

for an open and closed tube.

 

3. Describe what happens to sound waves to produce a beat.

Table 15: Rubric for Evaluation of Sound Question Three

 

1 point

A partial explanation is given.

 

 

2points

 

Response identifies the constructive and destructive interference that

takes place to produce a beat.

 

Topic: Reflection of Light

1. State the law of reflection as it applies to mirrors.

Table 16: Rubric for Evaluation of Reflection Question One

 

 

lpoint

 

Response states that the angle of incidence is equal to the angle of

reflection

 

40

 

 

 

2. Look at the drawing below of a laser hitting a curved mirror. The “C” stands for the
center of curvature and “F” stands for the focal point. For each diagram, draw in the ray

that is reflected off of the surface of the mirror.

 

 

 

   

Figure 6: Reflection of a Concave Mirror Question

Explain why you gave the reflected ray the path that you did.

Table 17: Rubric for Evaluation of Reflection Question Two

 

1-2 points A partial explanation is given.

 

 

3 points Each ray is given the correct path. Response uses a line through the

center for measuring angles.

 

 

3. When a laser reflects Off of a standard mirror, two rays are often seen leaving the
mirror. The two rays run parallel to each other. Explain what causes the one ray to

become two rays.

Table 18: Rubric for Evaluation of Reflection Question Three

 

1 point A partial explanation is given.

 

 

2 points Response identifies the ray reflecting Off the glass and off the silver.

 

 

41

 

 

Topic: Electrostatics

1. What is the Basic Law of Electrostatics?

Table 19: Rubric for Evaluation Of Electrostatics Question One

 

1 point A partial explanation is given.

 

 

2 points Response states that opposite charges attract and like charges repel.

 

 

2. What is the difference between charging an object by conduction and charging it by

induction?

Table 20: Rubric for Evaluation of Electrostatics Question Two

 

1 point A partial explanation is given.

 

 

2 points Response identifies that conduction requires contact, while induction
only requires close proximity. The response also includes a
description of conduction charging the second Obj ect with a like

charge, while induction produces an Opposite charge.

 

 

3. How does a lightning rod attract lightning to it?

Table 21: Rubric for Evaluation of Electrostatics Question Three

 

I point A partial explanation is given.

 

 

2 points Response describes the electric field near a potential conductor as

being stronger than the surrounding area.

 

 

42

 

 

 

Appendix A-II: Semester Two Pretest/Posttest Questions with Evaluation Rubrics

Topic: DC Circuits

1. Describe the property of resistance.

Table 22: Rubric for Evaluation of DC Circuits Question One

 

1 point

A partial explanation is given.

 

 

2 points

 

Response describes resistance reducing the flow of current through a

material.

 

2. Describe a way to connect two resistors together in a circuit so that less current is able

to flow through the circuit.

Table 23: Rubric for Evaluation of DC Circuits Question Two

 

1 point

A partial explanation is given.

 

 

2 points

 

Response describes a series circuit and refers to it by name

 

3. Describe a way to connect two resistors together in a circuit so that more current is

able to flow through the circuit.

Table 24: Rubric for Evaluation of DC Circuits Question Three

 

1 point

A partial explanation is given.

 

 

2 points

 

Response describes a parallel circuit and refers to it by name.

 

43

 

 

 

Topic: Newton’s Laws

1. Describe Newton’s First Law, Inertia.

Table 25: Rubric for Evaluation of Newton’s Laws Question One

 

lpoint

A partial explanation is given.

 

 

2 points

 

Response correctly describes inertia.

 

2. Describe Newton’s third law.

Table 26: Rubric for Evaluation of Newton’s Laws Question Two

 

1 point

A partial explanation is given.

 

 

2 points

 

Response correctly describes equal and opposite forces.

 

Topic: Force Components

1. Imagine the car below sitting on an inclined plane. The wheels have been blocked to

keep it fiom rolling down. Use arrows to show all forces acting on the car.

4

    

Figure 7: Force Components on an Inclined Plane Question

 

 

Table 27: Rubric for Evaluation of Force Components Question One

 

1 point

Most forces are present but some are missing.

 

 

2 points

 

Response correctly shows all forces

 

2. For each force labeled in number 1, describe the relationship between that force and

the force of gravity.

Table 28: Rubric for Evaluation of Force Components Question Two

 

1 point

A partial explanation is given.

 

 

2 points

 

Response correctly relates each force to gravity.

 

Topic: Circular Motion

1. Two Objects are moving along circular paths. How is it possible for them to have the

same rotational speed but different tangential speeds?

Table 29: Rubric for Evaluation Of Circular Motion Question One

 

1 point

A partial explanation is given.

 

 

2 points

 

Response correctly identifies the paths as having different radii.

 

2. What is the critical velocity of an Object on a circular path? What is the main factor

that affects the critical velocity?

45

 

 

 

Table 30: Rubric for Evaluation of Circular Motion Question Two

 

1 point

A partial explanation is given.

 

 

2 points

 

Response correctly describes critical velocity and identifies the radius

of the path as the main factor.

 

Topic: Rotational Motion

1. What two quantities are related to the torque on an object?

Table 31: Rubric for Evaluation of Rotational Motion Question One

 

1 point

A partial explanation is given.

 

 

2 points

 

Response correctly identifies both force and length.

 

2. What two quantities must be zero for an object to be in equilibrium?

Table 32: Rubric for Evaluation of Rotational Motion Question Two

 

1 point

A partial explanation is given.

 

 

2 points

 

Response correctly identifies both net force and net torque.

 

46

 

 

 

Appendix A-III: Questions Represented on the Semester One Exam

1. Using Archimedes’ Principle, explain Why some objects sink and some objects float.

Table 33: Rubric for Evaluation of Semester One Exam Question One

 

 

 

1 point Response includes a description of a buoyant force being equal to the
weight of the displaced fluid

2 points Response includes an explanation that the buoyant force equals the
weight of the Object for the Object to float.

 

 

2. In an experiment, 50 g of copper and 50 g of water are each heated to 90°C. Which of
the two contains more energy? Explain why you chose the one that you did using the

term specific heat in your explanation.

Table 34: Rubric for Evaluation of Semester One Exam Question Two

 

1 point Response states that the water has more heat energy

 

 

2 points Response correctly relates the above to specific heat

 

 

3. What is the relationship between a wave’s frequency and its wavelength?

Table 35: Rubric for Evaluation Of Semester One Exam Question Three

 

1 point A partial explanation is given.

 

 

2 points ReSponse identifies the relationship as inverse.

 

 

47

 

 

 

4. What is the difference between the properties of reflection, reflection and diffraction?

Table 36: Rubric for Evaluation of Semester One Exam Question Three

 

 

 

 

1 point Response includes one property correctly described.
2 points Response includes two properties correctly described.
3 points Response includes all three properties correctly identified.

 

 

48

 

Appendix A-IV: Example Homework Questions
Each topic area contains example homework questions given to the students using
the LON-CAPA system described in the implementation portion of this paper. When the
student submits responses via the intemet, the response will be either correct or incorrect
for the entire group of questions. If any one response is incorrect, the student will be told

incorrect, without any feedback about the number or identity of the incorrect responses.

Topic: Fluid Forces

Label each of the following statements as true or false.

Absolute pressure is always less than or equal to gauge pressure.

In a hydraulic device, the pressure is equal everywhere throughout the device.
A buoyant force acts in a downward direction.

The amount of pressure is directly related to the size of the area it acts upon.
When an Object floats, the buoyant force is equal to the force of gravity.

Some fluids do not have a definite volume.

Topic: Thermal Energy

Most materials increase in size when their temperature increases.

When water is heated in a container, the container gets hotter than the water.
As water boils it continues to get hotter.

When an Object is heated, the particles that make it up move faster.

When a solid with a hole in it is heated, the hole gets smaller.

All materials require the same amount of energy for a temperature change.

49

If 100g of water and 100g of lead are each at 90 °C, the lead contains more heat energy.

The quantity known as specific heat relates energy to both volume change and mass.

Topic: Wave Properties

Identify each statement as true or false.

When a straight wave pases through a small opening, it produces a small straight wave.
A wave will always reflect Off of a barrier at the same angle that it hits.

As the frequency of a wave increases, its wavelength decreases.

As a wave changes media its speed changes.

The speed of a wave is determined by its medium.

Two waves traveling through the same medium meet, they will combine to form a new
wave.

During diffraction, a wave bends because it hits the edge of a barrier.

A straight wave heads into a curved surface. It will reflect into a central point.

Unless it is disturbed each point on a wave will travel along either a straight or curved

path.
Refraction is the bending of a wave because its speed changes.

50

Appendix A-V: Student Opinion Survey
Opinion Survgy on Student Demonstrations
Please read each of the statements below and rate it 1-5 based on the following scale.
5. I strongly agree with the statement.
4. I agree with the statement.
3. I neither agree nor disagree with the statement.
2. I disagree with the statement.

1. I strongly disagree with the statement.

__ Watching the classroom demonstrations helped me learn the material.
__ I enjoyed watching other students perform demonstrations.

__ Preparing and presenting demonstrations helped me learn the material.
__ The demonstrations that my group did went well.

__ Working in groups is a good way to prepare demonstrations.

I enjoyed preparing and setting up the demonstrations.

I enjoyed presenting the demonstrations to the class.

51

Appendix B: Physics Demonstrations

Appendix B-I: Fluid Mechanics Demonstrations
Part 1: Water Bottle Boats - Archimedes’ Principle

This demonstration will show that when a boat floats, it displaces enough liquid to equal

its weight.

Collect the following Materials:

3 large graduated cylinders 1500 ml water (tap water is ok)
3 20-24 oz drink bottles 1500 ml alcohol

sand - 1500 ml glycerine

3 200 g masses food coloring

1. Cut the tops Off of the drink bottles.
2. Add enough sand to the bottles so that each has a total mass of 100 g.
3. Add a different color of food coloring to each of the liquids and place each in a

graduated cylinder.

, The three graduated cylinders are placed in an observable location. One has 1500 ml of
water, the second has 1500 ml of alcohol and the third has 1500 ml of glycerin. Each has
been colored a different color with the food coloring. The presenter places a boat of mass
100 g into each liquid. It is Observed that the boat in the water displaces 100 ml of water,

the boat in the glycerin displaces less and the boat in the alcohol displaces more.

Figure 8: Equal Masses in Different Liquids

 

52

A 200 g mass is added to each boat. It is observed that in each cylinder, the boat lowers
into the liquid and the liquid level rises. The liquid’s density determines the amount that
needs to be displaced. The presenter will then show how to use the mass of the boat and

the volume Of the displaced water to calculate the density of each liquid.

Explanation:
Why does an Object in a fluid seem to be lighter? When an Object goes into a fluid, it

must push the fluid out of the way. We say that the fluid is displaced.

Newton's Third Law says that for every force there is an equal and opposite force. This
means when the object pushes on the fluid, the fluid pushes back on the object. This is
called a buoyant force. The buoyant force works opposite to the force of gravity and lifts
the object.

Archimedes' Principle describes the strength of the buoyant force on a Object. It states:

The buoyant force on an object is equal to the weight of the fluid that it displaces. .
An object floats when it displaces enough of a fluid to equal its weight. For example,

when a boat is put into the water, it sinks into the water until the weight of the water

being displaced is equal to the weight Of the boat.

53

When you get into the boat, it sinks deeper into the water. It displaces enough water to
equal your weight and the weight of the boat. If the boat is carrying too much weight, it

cannot displace enough water and it sinks.

Whether an object floats or sinks in a fluid depends on its mass as it compares to its

volume. The ratio of an object’s mass to its volume is called its density.

Part 2: Pressure Fountain

This demonstration illustrates the concept that fluids move from areas of high pressure to

areas of low pressure.

Materials

1 1000ml erlenmeyer flask with 30-40 cm of latex tubing
outlet port food coloring

l #8 1 hole rubber stopper 1 ring stand with iron ring
30-40 cm glass tubing 1 hose clam

2 1000 ml beakers

1. Construct the device as shown in the

diagram at the right.

 

 

Figure 9: Pressure Fountain

54

2. Place 300 ml of water in the flask, stopper the flask and invert. Place the glass tube

under the water in the lower beaker. Have the latex hose run into the second beaker.

How does it work?

Fluids move fiom areas of high pressure to areas of low pressure. When the flask is
inverted, water runs out Of the latex tube. As the water level lowers, this creates a larger
volume for the air in the flask. According to Boyle’s Law, the larger volume causes a

lower air pressure in the flask.

The water in the lower beaker has the weight of the atmosphere resting on it and is
therefore at a higher pressure than the air in the flask. The higher pressure pushes the
water up into the flask. This process is in a cycle and everything happens at the same

time. If the intake tube is plugged, no water is released from the outlet hose.

The Demonstration:

Begin with an analogy of drinking through a straw. Ask the question, “Could we drink
through a straw if there was no air ” Have the class consider an astronaut on .the moon.
Hehasalargetankofwatervvithanopentop. Asfiawnmsfiomthetankthrougha

sealed opening in his helmet and to his mouth. Can he drink fi'orn the tank? If he could,

there would be no point in the demonstration so the answer must be “no”.

55

Demonstrate the fountain and describe how it works. Now describe how a straw works.
Explain that as you remove the air from your mouth, the air pressure on the liquid pushes

it up into your mouth. If there is no difference in pressure, the liquid does not move.

Ask the class what will happen if the outlet hose is placed in the intake tank. The

fountain stops because there is no difference in pressure.

Part 3: Floating Balls

This demonstration uses Bernoulli’s Principle to make a ball float in air.

Materials:

Air source Ping pong ball
Various sizes Of Styrofoam balls Funnel

The Demonstration:

Attach the funnel to the air source. Place the ping-pong ball in frmnel. Ask the class to
predict what will happen when the air source is turned on. Demonstrate that when the air
is turned on, the ball does not leave the funnel. Further demonstrate that the funnel can

be inverted and the ping-pong ball remains in the funnel.

Setuptheairsourcetoproduceavertical stream. Placetheballsinthestreamsothat

they float in the stream. Describe how the moving flow of air is able to support the ball.

56

How does it work?

Bernoulli’s Principle states that a moving stream of fluid exerts less pressure than the

surrounding fluid. In the first case, the air moves in a stream around the ball.

 

   
 

Figure 10: Air Flow Around
A Ball in a Funnel

The moving streams are at a lower pressure than the surrounding area. The higher

pressure surrounding the ball pushes the ball into the funnel to keep it from falling out.

This principle will work whether or not the funnel is
present. In the second demo, the ball can be

supported on the stream. The slower moving air on

 

the outside exerts pressure on the ball to keep it in the

Figure 11: Air Flow Around a

' BallinanAirstream

Credits:
Parts 2 & 3: Doherty, Paul and Rathjen, Don. 1996 The Spinning Blackboard and Other

Dynamic Experiments on Force and Motion. John Wiley and Sons. 3 .

Part: Walpole, Brenda 1988. 175 Science Experiments to Amuse and Amaze Your

Friends. Random House. 33.

57

Appendix B-II: A Collection of Heat Demonstrations

Materials:

Ball and ring set Water

Balloon 2 150 ml beaker

Lab Burner 1 pan

Paraffin wax 2 thermometers

Set of metal samples (Cu, Fe, Al, Zn) Balance

Hot plate Ring stand and clamps

Beaker Gooseneck Camera with TV

Tongs Paper CUP

Lead shot Pipestem Triangle
Part I: A Hole in a Solid

Pose the following problem to the class. “You have a piece Of metal with a hole in it. If

the metal is heated, does the hole get bigger or smaller?”
Allow for discussion and let each student predict the correct answer. Get out the ball and
ring model. Show that the ball does not pass through the ring at room temperature. Heat

the ring in the lab burner. Show the class that the ball will now fit through it.

This happens because of the motion of the atoms in the metal ring. As the temperature

increase, the atoms move faster and increase the space between them. This makes the

58

entire metal expand, including the hole. This can be shown by drawing several dots and a
circle on a deflated balloon. When the balloon is inflated, it is noted that the dots are

farther apart and the circle is bigger.

Part II: Smific Heats of Lead and Water

Pose the following problem to the class.

You have two beakers. One contains 100g of solid lead the other contains 100g of water.

Each is heated to the same temperature. Which will better be able to melt wax that is put
in it?

Allow students to voice their opinions. Let each student predict the answer. Set up the
equipment as shown below. Place 100g of lead in one beaker and 100 g of water in the
other. Heat the larger beaker for the hot water bath on the hot plate and monitor the
temperatures Of the two smaller beakers. When the temperature Of the small beaker is
between 80-100 °C, remove the beakers from the water bath and place them on the table.
Remove the water first. Have the gooseneck camera set up to show the activity in the
small beakers. Place a small piece of wax in each beaker. Note that the one in the water

melts quickly and the one in the lead hardly melts at all.

vvater

 

lead
Most students will usually predict the lead, but \

the specific heat of the water is much greater

 

than the lead. This means that for the same

 

mass at the same temperature, the water

 

Figure 12:Heat of Lead and Water

59

contains more heat energy. People think of metals as “hotter”. This is because it has
such a low specific heat that its temperature will increase significantly with a small
amount of energy. A metal can have a very high temperature and still contain less

energy than a cooler mass of water.

Part III: The Great Metal Race

Before the demonstration, you will need to make a wax pancake. Melt some paraffin
wax and pour it out on the lab bench. You want it to cover a large area but not very
thick. Make sure that it is cool before you begin. Suspend the wax pancake over the lab

table.

Set up a hot water bath. Connect the four metal samples together and place them in the
bath. If the samples have hooks on them they can be connected by hanging them on a
bent coat hanger. If there are not books, they can be connected with a string. Make sure
that this is set up so that the metals each have some space between them._ Explain to the
class that you will set the masses on the wax and they will melt through. Ask the
students to predict the order that they will fall through. Remove the masses from the
bath and place them on the wax pancake. Have the camera in position to observe the

masses falling through the wax.

6O

After the demonstration, you should note that the order is the same as the order of their
the specific heats. At the same temperature, the metals with the higher specific heats

contain more heat energy and are better able to melt through the wax.

Part IV: Boiling Water in a Paper Cup

This classic demonstration shows that a set of objects in
contact with each other heat as one object. The paper cup is
placed on a pipestem triangle above a lab burner. The water is
heated to boiling without the cup catching on fire. This

demonstration takes a few minutes and it is best to set it up and

 

let the water heat while the other demonstrations are going on. Figure 133 Boiling
Water in a Paper Cup

So why doesn ’t the cup catch on fire? This is the question that makes this demo
interesting. Heat transfers fiom high temperature to low temperature. As the cup heats
up it transfers the heat energy to the water. The water boils at 100°C so the cup never
gets above that temperature. The paper will only burn if the temperature gets above its
flash point. It never gets there because the water absorbs the heat. Even once the water
is boiling the cup still does not burn. The water is still absorbing the heat energy. It
cause the water molecules to move faster and change fiom the liquid state to the vapor
state. 1

Credits for Part 2: Heimler, Charles H. and Paul W. Zitzewitz. 1989. Focus On Physical

Science Teachers Edition. Merrill Publishing. 113.

61

Appendix B-III: Ye Olde Ripple Tank Demo

This demonstration uses a ripple tank to show a variety of wave properties. Most of the

equipment listed below can be found in a standard physics lab.

Materials:
Ripple Tank
Wave Generator

Light Source

 

Tall Ring Stand

Goose Neck Camera and TV

 

Glass Blocks

 

Hose Figure 14: Ripple Tank

Drain Bucket
Strobe Light

Plain White Paper
Set up the ripple tank on a level surface. Adjust the tank so that the water has a uniform

depth. Set up the gooseneck camera so that the observation surface is seen on the TV

screen. Pass out paper to each student.

62

Have the students fold the paper so that there are six squares on a side. Lead the students
through each demonstration and have them make observations for each. In any step the

strobe light can be used to make the wave appear to stand still for easier observations.

Part 1: Rectilinear Propagation
Use the wave generator to make several straight waves. Point out to the students that the

waves travel in straight lines and this property is called rectilinear propagation.

Part 2: Rectilinear Propagation from p Point 80%

Use a pencil to create a wave in the center of the tank. Note that the wave travels as a
circle away from the point. The question then is why does this wave not travel in a
straight line. The answer is that it does. Each point along the wave crest travels straight

away from the source creating a circle.

Part 3: The Relationship Between quencv and Wavelength

 

Use the wave generator to change the frequency of the wave. Notice that as the
frequency increases, the wavelength decreases. The speed of a wave is determined by its
medium. If the frequency increases, there are many waves traveling at the same speed, so

they get closer together.

Part 4: Reflection of a Straightflave fi'om a Strai t Barrier

Make a straight barrier in the tank out of two glass blocks. Align it so that the waves

strike the barrier at an angle. Send several straight waves toward the wall. Notice that the

63

angle of incidence is equal to the angle of reflection. You can verify this by changing the

angle of the wall. Notice that the angle of reflection also changes.

Part 5: Reflection of aC_urved vae Prong Straight Barrier

Leave the glass blocks in the tank. Make a wave from a point source as in part 2. Notice
how the shape of the wave inverts itself after it hits the barrier. This is because the parts
of the wave reflect in the order that they hit. The lead edge hits first and makes it invert

as the rest of the wave reflects.

Part 6: Straight \flves from a Curved Bgarrier
Replace the glass blocks with a thick piece of garden hose. Bend the hose to form a
curved barrier. Allow several straight waves to hit the barrier. Note the point at which

the waves converge. This point is referred to as the focal point.

Part 7: Diffraction of a Wave on :1 Corner

Remove one of the blocks. Adjust the one in the tank so that its edges are clearly seen.
Start the wave generator and note the curving of a wave as it passes the edge of the block.
The curving is caused by the slowing of the wave near the edge of the block. The speed
of the wave is determined by the medium. ‘ Although the wave is still traveling through

water, the fiiction between the water and the block does change its characteristics.

64

Part 8: Diffraction Throqu an Qppg g
Place the second glass block back in the tank so that there is a small opening between the

two blocks. Turn on the wave generator and notice the curved shape of the wave leaving

the opening. The wave diffracts on each edge around the opening and produces a curve.

Part 9: Refi'action of a Wave

Lay one of the flat blocks flat on the bottom of the tank. Adjust the water level in the
tank so that there is only a small layer of water over the top of it. Turn on the wave
generator. Notice the bending of the wave over the block. This bending is caused by a

change in speed of the wave.

Part 10: I_n_terference of M

Change the straight wave source for two point sources. Turn on the wave generator and
notice the pattern that forms. Where a crest meets a crest, a larger wave results. This is
called constructive interference. Where a crest meats a trough, a smaller wave results.
This is called destructive interference. You should be able to see strips of destructive

interference called nodes stretching across the tank.
Credits:

Trinklein, Frederick E. 1990. Modern Physics Exercises and Laboratory Experiments.

Holt, Rinehart and Winston. 235.

65

Appendix B-IV: Resonance: We Got the Beat

This is a collection of demonstrations on the principle of resonance.

Materials:

Two ring stands with cross bar small plastic mirror

String sound source (a signal generator or

3 200 g masses trombone)

tin can Tuning forks mounted on resonance boxes
balloon Tuning forks of various frequencies

laser Various lengths of pvc pipe

Part 1: A Coupled Pendulum
Two pendulums of about the same length are hung fiom a cross string. One is started
causing the other to start. It is observed that the motion of each pendulum starts and

stops m a regular interval.

As the first pendulum starts swinging, it pulls on the second; this starts the next one

moving. This continues, with the first giving energy to the second on each swing. Once

66

the first pendulum stops, the second one begins to pull on the first. And the cycle
continues.

This is an example of sympathetic resonance, one

vibrating object setting up a vibration in the second.

Resonance in sound waves works the same way.

F' 15: A C l d
Sound waves set up air vibrating in a closed space. P335111“! oup e

Part 2: Resonating Tubes

Use the tuning forks to produce sounds of known frequency. Cut the pvc pipe to the
correct lengths and demonstrate that the correct frequencies will cause the tubes to
resonate. This is an example of sympathetic resonance, the tuning fork sets up the right
wave in the tube and it resonates. This can further be illustrated with the tuning forks
mounted on the resonance boxes. When the frequencies of the tuning forks match,

starting one vibrating will cause the other to start vibrating.

During setup it is important to prepare lengths of tubes so that they will resonate at the
correct fiequency. From the desired fiequency calculate the wavelength using the
formula:

v = fit

where v is the speed of sound in air, f is the fi'equency and k is the wavelength.

67

The length of the tube is dependant on it being an open tube or a closed tube. For an
open tube, the length is calculated using the equation:

9» = 2 1
An open tube resonates with a standing wave that has an antinode at each end. Multiples

of that frequency will also cause resonance. These multiple resonant frequencies are

called harmonics.
V v V V V
Fundamental Second Harmonic Third Harmonic

Figure 16: Open Tube Harmonics

For a closed tube, the length can be calculated using the equation: i=4]
A closed tube resonates with a standing wave that has an antinode at the open end and a

node at the closed end. Only odd multiples of the fundamental frequency will cause

resonance.
' I ' ' 1
3
Fundamental Third Harmonic . Fifth Harmonic

Figure 17: Close Tube Harmonics

The demonstrators must prepare several lengths of closed and open tubes before the

demonstration.

68

Part 3: Seeing Sound Waves

One final demonstration on this point uses a can with a balloon stretched over the
opening. A small light plastic mirror is glued to the balloon. A laser is shone on the

mirror and reflected onto a screen.

0%

 

Figure 18: Sound Visualization Demonstration

Use the sound source to produce a sound. Change the frequency of the sound and
observe the light. When the resonant frequency of the can is reached, the balloon will
vibrate and a pattern will show on the screen. With the right equipment, various

harmonics of the tube can also be shown.

Resonance will only occur when the frequency is right. Returning to the coupled
pendulum, it can be shown that if the lengths of string are very different, then the
sympathetic vibration will not occur. It can also be shown on the tuning fork boxes, when

the frequencies are not close the second box stays silent.

69

Part4: Beats

When sormd waves that have close frequencies combine together they produce audible
swells and lows. These swells are called beats. This was already shown with the coupled
pendulum. It can also be shown with the tuning fork boxes. When the forks are adjusted
so that their frequencies are only off by a few hertz, playing both shows this principle.

The following diagram shows the interference pattern of the sound waves.

W t 15V 1 W; M
W' m

  
    

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 19: Beats

Credits: Part1: The Coppled Pendulum came from the book:
Doherty, Paul and Rathjen, Don; The Spinning Blackboard and Other Mpamic

Em’ cuts on Force and Motiop; John Wiley and Sons, 1996.

The diagram in part 4 was taken from the web site:
hgpzlmmgphxsics.ph1-astr.gpu.edulhbaselsound/beathtml

70

Appendix B-V: The Laser Spirograph

A Spirograph is a drawing toy that turns one circle inside of another to make interesting

patterns. The same principle can be used to draw patterns with a laser.

Part I: Construction

Materials:

2 concave mirrors 1 screen

2 1.5-3.0 V motors ' 6 wires

1 3V DC source 2 25!) rheostats
1 ring stand with cross bar 1 hot-glue gun
2 buret clamps 1 fog machine

1 laser

1. Use the hot glue gun to connect the mirrors to the motors. The mirrors need to spin

with the motors.

2. Assemble the materials as shown in the diagram below. The buret clamps are used to

connect the motors to the ring stand.

71

 

 

Concave

mirror
1.5-3.0 laser
V motor

 

 

 

 

 

 

 

 

l

l“
I
Ill

 

 

 

 

' .
‘4—

 

 

L

 

 

 

L
I
Figure 20: The Laser Spirograph 259 rheostat I

3. The most challenging part of construction is the alignment of the mirrors. The laser
should hit the first mirror ofi‘ center. Spin the first motor and you will notice that the
reflected beam makes a circle. Adjust the position of the second mirror so that the entire
circle falls on the mirror surface, but is not centered on the vertex of the mirror. Finally
adjust the mirrors so that the rays reflecting off the second mirror hit the screen as

desired.

72

Part 11: How does it work?

All mirrors reflect based on the law of reflection. The angle of incidence is equal to the

angle of reflection. This is easy to visualize on a plane mirror.

Angle of Incidence

 

Angle of Reflection

Figure 21: The Law of Reflection
These angles are measured against an imaginary line that is perpendicular to the surface
of the mirror called the normal line. A concave mirror reflects based on this same law.

The normal line for a concave mirror is the radius of the curve.

 

 

Figure 22: Reflection on a Concave Mirror
Like anything that spins, the mirror will “wobble” due to precession. This wobble
changes the position of the normal line and therefore the position of the reflected beam.

Because the wobble has a circular path, the reflected ray makes a circle. Because the

73

wobbles of the two spinning mirrors are not in phase with each other, the spiral patterns

result.

When the mirrors are still wh do we see more than one int of li t on the screen?

 

Mirrors have a silver backing and a coating of glass on the front. The laser light reflects
twice on the mirror, once on the glass and once on the silver. This creates two reflected
rays. These two rays then reflect ofi‘ the glass and the silver of the second mirror to

produce the multiple dots.

Figure 23:
Reflection on Two
Surfaces

 

Why do we see a pattern and not just a mint of light moving in a pattern?

The answer to this says more about your eyes and less about the device. When you look
at something, its image lingers for a moment. This is most noticed when you look at a
bright light and then look away. You see the image after the fact. The image of the point
of light lingers as the point of light moves. This creates the appearance of a pattern. At
any moment, the ray of light is only at one point. If a picture of the pattern is taken, it
will show an image that is incomplete. This is because the shutter speed of the camera is

faster than the retention time in your eye and does not capture the entire image.

74

Part III: The Demonstration

Begin the demonstration by showing the laser light show. Turn on the motors and make
various patterns on the screen by adjusting the speed of the motors. The pattern can also
be affected by adjusting the spacing between the mirrors. This, however, can be difficult.
The use of a fog machine can make the show more spectacular.

In the process of explaining, shine a laser at a plane mirror mounted on a magnet attached
to the chalkboard to show the law of reflection. If the mirror is positioned so that the
normal line is parallel to the ground, then a gravity protractor can be used to measure the
angles of incidence and reflection. Change the position of the laser to show that changing
the angle of incidence will cause an equal change in the angle of refraction. Use the fog

machine to illuminate the beams.

Change the mirror to a concave mirror mounted so that the primary axis is parallel to the
floor. Draw the primary axis and label the center of curvature. Shine the laser on the
surface of the mirror from various angles to show that the law of reflection holds true for
a curved mirror also. Remember that the normal line is a radius of the circle.

It is a common misconception that a ray reflected from a concave mirror passes through

the focal point. This is only true if the ray is parallel to the primary axis.
Turn the laser Spirograph back on and point out the wobble in the mirrors. Explain how

the wobble creates a circular pattern and the second mirror changes the pattern. This can

be illustrated by only running one mirror.

75

Appendix B—VI: The Great Ball of Death

(A Collection of Demonstrations Using a Van deGraaff Generator)

These demonstrations use a Van deGraaff generator to illustrate a number of points about

electrostatics.

Materials:

Van deGraaff generator
Discharge wand

Tin can

3 metal plates

Styrofoam board for insulation
5 aluminum pie pans

1 Spring

stn’ng

tape

thin wire

aluminum foil

2 styrofoam balls, 4 cm diam.

1 stryrofoam ball, 15 cm diam.

    

Figure 24: The
Van deGraff
Generator

Large erlenmeyer flask

1 metal coat hanger

2 small metal balls

1 plastic milk crate

2 long insulated wires with alligator

clips

76

Part 1: Discharge

Plug in the Van deGraaff generator and turn it on. Hold the discharge wand near the
sphere on top and notice the sparks that discharge off. Sparks discharge because fi'iction
builds up a negative charge on the ball until the electric field becomes strong enough to

carry the charge to the discharge wand.

Inside of the base is a motor that spins the belt on a felt covered cylinder. The fiiction
causes electrons to leave the felt and travel on the belt to the sphere. The excess electrons
give the sphere a negative charge. The discharge wand is connected to the ground port on
the base. When the discharge wand is brought near the charged sphere, some negative
electrons near the surface of the wand are repelled according to the Basic Law of
Electrostatics:
Opposite charges attract and like charges repel.

An electric field exists between the sphere and the discharge wand. When the field
becomes strong enough, the-excess electrons will jump fi'om the sphere to the wand.

Making each momentarily neutral.

+
_ _ + +
_ —' +H
_ _ _ +
Figure 25: Induced Charge

Hint: To turn off the generator without being shocked, touch the discharge wand to the sphere while 3

touch the controls.

77

Part 2: A Hair Raising Exgrience

For this next part, you will need a volunteer to help out. A good volunteerhas fine,
medium length hair without hair spray. Have the person stand on the milk crate and

touch the generator. Turn it on and wait a minute. The person’s hair stands on end.

When an object is charged, the charge spreads across its surface. For a person, each of

the hairs gets the same charge and they repel each other.

When the person is done, use a meter stick to turn off the generator before the person lets
go. DO NOT DISCHARGE THE GENERATOR WHILE THE VOLUNTEER IS

TOUCHING IT. THEY WILL GET A SHOCK!

Part 3: Flflp' g Pans

Set the tin can on the generator and place a metal plate on top of it. Stack up the five
light aluminum pie pans on top of it. Turn on the Van deGraafl‘ generator and wait a
minute. As the charge builds up the pans will each have the same charge and will repel

each other. They will fly off of the plate one at a time.

78

Part 4: Franklin’s Bell

Mormt two metal plates vertically on the foam board
with a distance of 15-20 cm between them. Set the
board on a stool or a milk crate. Connect the plates to
the Van deGraaff generator. Use the insulated wires
to connect one plate to the sphere and the other plate

to the ground.

 

Cover a small Styrofoam ball with aluminum foil and
hang it flour a string. Position the hanging ball so Figure 26: Franklin’s Bell
that it is between the plates. Turn on the generator

and observe the motion of the ball between the plates.

When the generator is turned on, the plates get opposite charges.

 

Furthermore, a charge is induced in the ball that is opposite the

 

charge in the plates. The opposite charge on the ball is attracted
to a plate and moves. over until the ball hits the plate. When the
ball hits a plate, it is charged by conduction and has the same

— ‘ charge as the plate that it hits.

 

Figure 27 : Conduction and
Induction in Franklin’ Bell

79

Once the ball has the same charge, it is repelled by the first plate and
swings to the second plate where it gets the opposite charge and is

again repelled and the cycle continues.

Part 5: Sm' g (firpbals

Suspend a spring by a string from the ceiling. Attach a metal plate to the bottom of the
spring so that the plate is parallel to the ground. Set another metal plate on the Styrofoam

board resting on the milk crate. Align the two plates so that they are 10-15 cm apart.

Connect the Van deGrafI generator to the
spring and the bottom plate. When the
generator is turned on, the upper plate

accumulates a negative charge through

 

conduction and the lower plate gets a positive
charge through induction. The opposite

- Figure 28: Spring Cymbals
charges attract and the plates are pulled

together.

Once the plates touch, the charges are neutralized and the spring pulls the plate back up.

80

Credits:
Parts 3 and 4 were adapted from descriptions and diagrams fi'om the Physics
Demonstration Lab at the University of Michigan. The information is available online at:

http://www.physics.lsapurrrich.edu/demoLab/index.htm

Part 5 was adapted from diagrams fiom the Physics Department at the University of
California at Bereley. It can be viewed at:

ht_tp://www.mip.berkeley.edulrfiysicp/D—Iflflhtml

81

Appendix B-VII: Be it Ever So Humble, There’s Nothing Like Ohm

This demonstration will examine Ohm’s Law and the distribution of voltage and cmrent

through a circuit.

Materials:

DC power source Alligator clip wires
Voltrneter Gooseneck camera and TV
Ammeter Overhead Projector
Uninsulated copper wire Nails

Play dough

Part I: Ohm’s Law

Ohm’s Law describes the relationship between voltage, current and resistance. It is best
described with the mathematical formula:

Y_=_
This first demonstration will show that at a constant voltage as the resistance of a

material increases, the current decreases. Make a snake of play dough 2-3 cm in diameter

and 10-15 cm long. Set it on the overhead projector. Position the gooseneck camera so

82

that the meters can be seen on the television. Connect alligator clip wires to the elements

as shown in the diagram below.

 

 

Voltrneter

DC Source

 

 

 

 

 

 

 

 

 

\

Play Dough Snake

 

 

 

 

 

 

 

 

 

Figure 29: Ohm’s Law Demonstration

Place the probe in the play dough. Adjust the voltage and show that increasing the
voltage increases the current. Then leaving the voltage constant, move the probe along
the play dough so that you are increasing the distance between the probes. This will

increase the resistance in the circuit and decrease the current.

Part H: Resistors in Series

Make three play dough resistors, each tube should be 3-4 cm in diameter and 5-6 cm
long. Also cut several lengths of bare copper wire each about 10 cm long. In this part of
the demonstration we will be measuring current at a constant voltage. Remember that a

decrease in current means an increase in resistance, for a constant voltage.

83

 

1‘18“!" i I rr—u- ..

Set up one resistor and record the current flowing through it. Then use the copper wire to
connect two together in series. You should notice that the current is approximately one-

half of its original value. Now connect the third one in series and notice that the current

is approximately a third of its original value.

 

 

Ammeter

 

 

Figure 30:
Resistors in Series

 

 

 

 

 

Pprt III: Resistors in Parallel

Now connect two resistors in parallel. Notice that the total current is approximately
twice that of a single resistor. This is because electricity has two paths to follow resulting

in an overall circuit resistance that is less than that of a single resistor.

 

DC Source

 

 

 

Figure 31:
Resistors in
Parallel

 

 

Ammeter

 

 

 

84

Part IV: Resistog in Series and Parallel

Finally, connect a circuit with two resistors in series connected to a single resistor in
parallel. Use this setup to show the following.

1. The voltage is equal or each side of the parallel circuit.

2. The two resistors in series divide the voltage.

3. There is more current flowing through the lower resistance.

   

Figure 32:
Compound Circuit

Credits: This lab was adapted from an experiment on resistivity produced by the Physics

Department at Northern Kentucky University. Their experiment can be viewed at:

ht_tp://physics.nku.edu/GeneralLab/21 1%2OResistivity%_20Resis-clay.html

85

Lab Observations: Be it Ever So Humble, There’s Nothing Like Ohm
You will view a series of demonstrations presented by a group of students. In each case,
you will be asked to make a prediction, record your observations and write a concluding
statement to summarize the principle being shown.
Part 1
A. What will happen to the amount of current when the space between the probes is

increased?

B. What happens to the current as the space between the probes is increased?

C. Write a statement that explains why the above observations occurred.

Part 2
A. What will happen to the amount of current in the circuit as resistors are connected in

series?

86

B. What happens to the current as the resistors are connected in series?

C. Write a statement that explains why the above observations occurred.

Part3

A. What will happen to the amount of cmrent in the circuit as resistors are connected in

parallel?

B. What happens to the current as the resistors are connected in parallel?

C. Write a statement that explains why the above observations occurred.

Part 4

A. Which branch of the circuit will have the greater amount of current flow through it?

87

B. Which branch of the circuit actually has the greater amormt of current flowing through

it?

C. Write a statement that explains why the above observations occurred.

88

Appendix B-VIII: Newton’s Laws

Materials:

3- spring scale Rubber bands
large book 100 g mass
sting 500 g mas
Can

Part 1: The Inertil of a Book

 

 

 

Suspend a textbook from the ceiling by a thin
suing. Attach a second string to the bottom of the
book. Tell the class that you are going to pull
down quickly on the lower string. Ask them to

predict if the upper or lower string will break first.

 

Pull do 1 0 th strin , d th 1
wn sharpy n e g an e ower Figure 33:1nertiaofaBook
string will break. This is because the book’s

inertia resists the pull and breaks the string.

Replace the lower string. Now tell the class that you are going to pull down on the lower
string slowly. Again ask them to predict what will happen. Pull down slowly on the
string and the upper string breaks. This is because with the slow force, inertia is not as
much of a factor. The weight of the book puts more force on the upper string so it is the

first to break.

89

Part 2: Hangm' g Spring Scale:

 

Hang a spring scale so that all can see. Place the
500 g mass on the scale and observe its mass.
Remove the weight, hang a second spring scale
from first. Calibrate the scales so that each reads

zero. Ask the students to predict the reading on

 

each scale when the weight is hung from the lower
scale. Place the weight on the lower scale and Figure 34: Hanging

Spring Scales
observe that each scale shows the full weight.

At each point the weight being pulled down is equal to the force being pulled up. The
weight pulls on the bottom scale and the spring pulls back on the weight. The lower
scale pulls on the upper scale with its spring pulling back. The upper scale pulls on the

support stand even though it isn’t being measured.

 

 

 

Part 3: The Can Comes Back weight I can

 

 

 

 

 

Assemble a can as shown on the right. Roll it \

across the room and itwillreturn. This is because p <

of Newton’s third law. As the can rolls, the /

Rubber
the opposite force will push the can backwards. bands

    

 

 

weight winds on the rubber bands. As it unwinds

 

 

 

Figure 34: Returning Can

90

Lab Observations: Newton’s Laws
You will see a demonstration presented by a group of students from your class. You will
be asked to predict the outcome of the demonstration, record your observations and
explain the results.
Part 1: The inertia ofa book.
A. Predict which string will break when a Sudden force is applied to the bottom string.

Justify your prediction.

B. Which string actually breaks under a sudden force?

C. Explain the observation in part B.

D. Predict which string will break when a steady force is applied to the bottom string.

Justify your prediction.

E. Which string actually breaks under a steady force?

F. Explain the observation in part E.

91

Part II: Hanging Spring Scales
A. Predict the reading on each spring scale when two are hung end to end and the weight

is hung on it.

B. Observe what happens and record it below.

C. Explain why the scales read the weights that they did.

Part III: The Rolling Can
A. Predict what will happen to the can when it rolls across the floor.

B. Observe what happens. Record these observations below.

C. Explain the observations recorded in part B.

92

 

Appendix B—IX: Force Components

Materials

Small car lead shot

PVC inclined plane rack board for inclined plane
2 clamp pulleys protractor

2 small weight buckets spring scale

The inclined plane is set up in the rack. One pulley is mounted on the rack so that
the string coming from the front of the cart can run parallel to the plane and over the
pulley. The second pulley is positioned so that the string running from the center of the

car can run perpendicular to the plane and pass over the pulley.

Find the weight of the cart using the spring scale. Measure the angle of incline of
the plane. Calculate parallel force using the formula fp = fwsinO. The parallel force is the
component of the force of gravity that pushes the cart down the inclined plane. Place an
amount of lead shot into one of the weight buckets so that the total weight of the bucket
and the shot is equal to the parallel force. Now calculate normal force using the formula
fN = fwcose. The normal force is the component of the force of gravity that pushes the
cart into the inclined plane. Place an amount of shot into the other weight bucket so that
the total weight of the bucket and shot is equal to the normal force. The two buckets are
then placed on the appropriate strings. The board is removed but the cart does not move

because the hanging weight is taking the place of the board.

93

When an object rests on an incline plane, its weight is divided into two forces.
Part of the forces pushes the object into the plane. This force is called the normal force.
The other part pushes the object down the plane. This force is called the parallel force.
These two forces are perpendicular to each other and the weight of the object is equal to

their vector sum.

 

 

Figure 36: Force Components
on an Inclined Plane

The angle between flu and fW is labeled 0 and is equal to the incline of the inclined
plane. The parallel force, as the side opposite of the angle, is equal to the product of the
hypotenuse and the sine of the angle. (f, = fwsine) The normal force, as the side adjacent

to the angle, is equal to the product of the hypotenuse and the cosine of the angle. (fN =

fwcose)

When the object resting on the inclined plane is blocked, it will not move. The
block pushes on the object with a force that is equal and opposite to the parallel force,
and the plane pushes on the object with a force that is equal and opposite to the normal
force. Ifthese equal and opposite forces are replaced, the inclined plane is not necessary

to keep the object in its inclined position.

94

Credit: Trinklein, Frederick E. 1990. Modern Physics Teachers Edition. Holt, Reinhart

and Winston. T70F.

95

Lab Observations: Force Components
You will observe a classroom demonstration completed by a group of students from your
class. Answer the following questions based on the demonstration.

1. Draw a free body diagram for the car sitting on the inclined plane.

2. Calculate the normal force and the parallel force for the car.

3. Record your observations of what takes place during the demonstration.

4. Explain the observations in #3.

96

Appendix B-X: Going into a Spin

This collection of demonstrations is designed to highlight various principles of circular

motion.

Materials:

2 Tennis balls of different colors. 1 sturdy bucket with handle
String nails or water for the bucket

Part 1: Rotational SpeLd Comm to Tangential Sfied

Take two tennis balls. Make sure that they are different colors. Run a string through each
and secure it with a knot. Make the length of one string 1 m long and the second string
1.5 m long. Go outside where there is a lot of room. Swing both over your head
together. Point out to the class that both have the same rotational speed. This means-that
each will make the same number of rotations per minute. Now release the balls at the
same time. Notice that the one with the longer string goes farther. This is because it has
a larger tangential speed. Both balls are released from the same height and take the same
amount of time to fall. Therefore the one that is traveling the fastest horizontally will go

the furthest.

97

Part 2: Swing the Bucket

Get a sturdy bucket and fill it half way with either water or nails. Swing the bucket back
and forth, slowly increasing the size of the arc. Afier the bucket is moving at the critical

velocity, you will be able to swing it overhead without losing its contents.

As the contents are moving up, their inertia requires them to continue up or moving out
away from the center of the circle. For an object on a circular path this effect of inertia is
often called centrifugal force. The bucket (your arm) applies an unbalanced force on the

contents of the bucket and causes it to move on a circular path.

A question to consider is what would happen to the water if, while the bucket was at the
top of its arc, the bucket magically disappeared. Most students will predict that the water
would fall. This is not true. The water would continue horizontally and drop, following

the path of a projectile.

Credits:
Part] is from the book: Serway, Raymond A. and Jerry S. F aughn.2002. Holt Physics

Teachers Editiop, Holt, Reinhart and Winston. 253.

Part 2: Department of Physics and Astronomy at the University of Minnesota. 2001.

hgp://www.physics.umn.edu/gr_'oups/demo/demo_gifs/1D50 40.GIF

 

98

Lab Observations: Going into a Spin
You observe demonstrations on circular motion being presented by a group of students
from your class. Please answer the following based on the observations.
Part 1

A. Predict which ball will go farther when they are released. Justify your prediction.

B. Observe what happens to the balls when they are released. Record you observations

below.

C. Explain the observations in part B. Refer to the rotational speed and the tangential

speed in your explanation.

Part H: The Swinging Bucket

A. Predict what will happen to the bucket as it is swung over the demonstrator head.

B. Observe what happens during the demonstration and record it below.

C. Explain the observations recorded in part B.

99

Appendix B-XI: Don’t Rock the Boat

Materials:

1 large candle 1 hammer
2 large pins string

1 l2” ruler

Part 1: Burning the Candle Lt Both Epg

Trim the candle so that each end has a burnable
wick. Push the pins into the candle at the mid point
so that it is balanced. Suspend the candle between
two beakers and light both ends of the candle. The

Figure 37: Rocking
candle will rock back and forth on the beakers. Candle

Torque is the product of force and length. As an end to the candle burns it reduces in
both weight and length. The torque on that end reduces and that end of the candle rises.
The lower end will burn faster because of its position. When the torque on the low end

reduces enough, it will rise and the cycle continues.

100

Part 2: Dem g Gravig
Set up the ruler and hammer on the edge of a table as shown in the diagram. Draw a

diagram of it on the board or overhead and explain how all of the forces and torques are

balanced.
On the ruler, the upward forces must On the hammer, the upward forces
equal the downward forces. must equal the downward forces.

 

 

Figure 38: Forces on Ruler and Hammer

The torques around any fulcrum must also
be equal. In this case we will consider the

fulcrum to be the point where the ruler

 

meets the table. Notice that there are no

forces on the right of the fulcrum.

 

Figure 39: Torques on the Ruler
Credits:

Walpole, Brenda. 1988. 175 Science Experiments to Amuse and Amaze Your Friends.

Randomhouse. 97.

‘ 101

Lab Observations: Don’t Rock the Boat
You will observe a set of demonstrations being presented by a group of students fiom
your class. Complete the following based on these demonstrations.
Part 1: Burning the Candle at Both Ends.

A. Predict what will happen to the motion of the candle when both ends are lit.

B. Observe what happens to the candle when it is lit and record your observations below.

C. Explain the observations recorded in B.

Part II: Defying Gravity

A. Predict what will happen to the hammer and the ruler when it is released.

B. Observe the motion of the hammer and ruler and record your; observations below.

C. Explain the observations in B. Your explanation must include a free body diagram

and a description of the forces and torques acting on the system.

102

APPENDIX C: DATA TABLES

Table 37 : Comparison of Pretest and Posttest Data by Topic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Topic Average Pretest Average Posttest
Score Score
Fluid Mechanics 26.7% 74.7%
Thermal Energy 23.5% 87.3%
A Wave Properties 20% 88.3%
Sound 3.7% 68.5%
Reflection 18.4% 62.3%
Electrostatics 7.4% 88.0%
DC Circuits 9.8% 80.4%
Newton’s Laws 10% 83.3%
Force Components 36.7% 75.8%
Circular Motion 8.8% 69.1%
Rotational Motion 14.7% 89.7%
Average 16.3% 78.9

 

 

Table 38: Semester End Comparison for Target Questions

 

 

 

 

 

 

Topic Average Average Average
Pretest Score Posttest Score Semester Exam

Score

Archimedes’ Principle 3.3% 63.3% 61.1%

Specific Heat 29.4% 94.1% 100%

Wavelength-Frequency 53.3% 86.7% 91.7%
Relationship

Wave Properties 2.2% 82.2% 53.7%

 

 

 

 

103

 

Table 39: Comparison of Posttest Scores for Observers and Presenters

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Topic Average Presenter Posttest Average Observer Posttest
Score Score
Fluid Mechanics 75.0% 74.6%
Thermal Energy 88.9% 86.9%
Wave Properties 95.8% 86.5%
Sound 77.8% 66.7%
Reflection 72.2% 60.4%
Electrostatics 94.4% 86.7%
DC Circuits 83.3% 80.0%
Newton’s Laws 87.5% 82.7%
Force Components 87.5% 72.9%
Circular Motion 75.0% 68.3%
Rotational Motion 87.5% 90.0%
Average 84.1% 77.8%

 

 

 

104

 

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Anderson, Charles W. and Okhee Lee. 1997. Will Students Take Advantage of
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Carpenter, D. Rae Jr. and Richard B. Minnix. 1981. The Lecture Demonstration: Try It,
They’ll Like It. The Physics Teacher 19:392.

Deese, William C., Linda L. Ramsey, Jeffrey Walczyk and Danny Eddy. 2000. Using
Demonstration Assessments to Improve Learning. Journal of Chemical Education.
77:1 5 15.

Department of Physics and Astronomy at the University of Minnesota. 2001.
hpp://www.physics.umn.edu/groups/demo/demo:gifs/1D50_40.GIF

Doherty, Paul and Don Rathjen. 1996. The Spinning Blackboard and Other Dynamic
Experiments on Force and Motion. John Wiley and Sons.

Edehnan, Bruce and Steve Goeglein. 1995. Student Teachers. The Science Teacher
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Ewing, Phillip. Demonstration. 2000. Physics for Teachers. Michigan State University.
East Lansing.

Feynman, Richard P. 1988. The Cold Facts. “What Do You Care What Other People

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