Identifying Student Difficulties with the Propagation
of Mechanical Waves
Michael C. Wittmann, Edward F. Redish, Richard N. Steinberg
Dept. of Physics, Univ. of Maryland, College Park,
MD 20742-4111; 301-405-8090 (Wittmann), mwittman@delphi.umd.edu
To be presented 9 August 96 at the summer conference of the
American Association of Physics Teachers, held August, 1996 in
College Park, Maryland. Posted on the Web on 23 July 96.
Abstract (original version; talk has been
modified since then):
The Physics Education Research Group at the University of Maryland
has been conducting research into student understanding of mechaical
waves in our introductory calculus-based physics courses using
student interviews, examination questions, and a free response
diagnostic test. We have observed a number of common student confusions
in the area of waves on elastic strings. Based on our research,
we have developed student-centered instructional tutorials using
interactive video tools on the computer. We will demonstrate some
of these materials and discuss their effectiveness.
The talk was originally designed to be presented using a browser
(Netscape). Though it is all one document, the buttons can be
used to present the talk in slide format. A screen size of 800x600
is reccommended. Comments should be referred to MCW (email and
homepage listed below).
Proceed to talk.
Identifying Student
Difficulties with the Propagation of Mechanical Waves
Michael C. Wittmann, Edward F.
Redish, Richard
N. Steinberg
Physics Education Research Group
University of Maryland, College Park
Friday 9 August 96
1
Physics
Education Research Group, University of Maryland
Physics Education Research
Group,
University of Maryland 
2
Professor: Edward F. Redish
Post Doc: Richard Steinberg
Graduate Students: Lei Bao
Mel
Sabella
Jeff
Saul
Michael
Wittmann
Physics Education
Research Group, University of Maryland
Previous Research by
Others 3
- kinematics, superposition: Lillian
McDermott and Diane Grayson.
- propagation, superposition: Joseph Snir.
- sound waves: Gaalen Erickson and Cedric
Linder.
Physics Education
Research Group, University of Maryland
Motivation for Research
4
- The topic of waves is of fundamental importance
for understanding nature.
- Students make common errors. Are they
caused by systematic problems?
- First time students encounter a situation
where global and local effects are not the same.
- To understand sound, physical optics,
quantum mechanics, and other more advanced topics, students must
understand this material.
Physics Education
Research Group, University of Maryland
Population Studied 5
- Introductory, calculus-based university
physics course
- Engineering Students
- Course format:
- Lecture: 3 hours, large lecture class
- Lab: 2 hours
- Discussion: 1 hour, recitation or tutorial
Physics Education
Research Group, University of Maryland
Research Methods 6
- Free response conceptual quizzes
- Individual demonstration or problem solving
interviews with volunteers
- Specially written examination questions
- Diagnostic Waves Test given pre-course
and post-course
Physics Education
Research Group, University of Maryland
Underlying Concepts
7
- A disturbance propagates through a medium
without permanently displacing elements of the medium.
- Speed of propagation depends on the medium.
- Superposition of waves is the vector addition
of displacement due to each wave.
- Reflection and transmission depends on
boundary conditions.
Physics
Education Research Group, University of Maryland
Underlying Concepts
7.1
- A disturbance propagates
through a medium without permanently displacing elements of the
medium.
- Speed of propagation depends
on the medium.
- Superposition of waves
is the vector addition of displacement due to each wave.
- Reflection and transmission
depends on boundary conditions.
Physics Education
Research Group, University of Maryland
Research Question 8
Question:
A string is attached to a distant wall.
A pulse moving on the string reaches the wall in time t0.
How would you decrease this time?
Correct Answer:
increase the tension in the string
or
exchange the string to get a lower mass density.
Physics Education
Research Group, University of Maryland
Pre-Instuction Interviews:
Particle Waves 9
- The naive force idea:
ìYou flick it harder...you put a greater
force in your hand, so it goes faster.î
- Faster is faster, regardless of direction:
ìIf we could make the initial pulse
fast, if you flick it faster.....It would put more energy in.î
Physics
Education Research Group, University of Maryland
Pre-Instruction Interviews:
Massive Waves 10
- Small and feisty is faster,
- Bigger is better:
ìIíd send a quicker pulse, [smaller
in amplitude and width].... Or, I would make a huge pulse...I
could cover more area with one pulse.... The odd idea is that
I donít know which one would work better.î
ìThe one that was twice the amplitude
[would have the faster speed].î
Physics Education
Research Group, University of Maryland
Post-Instruction Interviews
11
Individual problem solving interviews with
9 students in the traditional discussion section were carried
out. Student comments mirrored those from previous interviews.
Change the tension (correct): 2 students
Hand motion plays a role: 6 students
Did not answer the question: 1 student
Physics
Education Research Group, University of Maryland
Pre-Course Waves Test 12
Asked in the first week of classes.
| Student Responses |
Pre Instruction |
Post Instruction |
Depends only on
medium (correct) |
6 % |
|
Depends on both medium
and hand motion |
18 % |
|
Depends only on
hand motion |
54 % |
|
| Other |
22 % |
|
Physics Education
Research Group, University of Maryland
Post-Course Waves Test 13
Asked in the last week of classes.
| Student Responses |
Pre Instruction |
Post Instruction |
Depends only on
medium (correct) |
6 % |
24 % |
Depends on both medium
and hand motion |
18 % |
72 % |
Depends only on
hand motion |
54 % |
3 % |
| Other |
22 % |
1 % |
Physics Education
Research Group, University of Maryland
Summary of Results 14
- Student idea of "waveness" jumbles
intensity, energy, force, amplitude, and speed.
- After traditional instruction, students still
have difficulty separating relevant parameters in wave motion.
- Many students do not distinguish between
global and local phenomena.
- We cannot expect students to understand these
concepts in electromagnetism, physical optics, quantum mechanics,
etc.
Physics Education
Research Group, University of Maryland
Curriculum Development 15
- Develop tutorials: student centered, group
work, guided discovery lessons which address these issues.
- Use demonstrations and videos of wave motion
on a spring, filmed at Dickinson College, Summer, 1995.
- This work is being done as part of Activity
Based Phyiscs: student engagement in learning emphasized.
Physics Education
Research Group, University of Maryland
Iterative Wheel of Research
16
Physics Education
Research Group, University of Maryland
Iterative Wheel of Research
17
Michael C. Wittmann
mwittman@delphi.umd.edu
Michael
C. Wittmann homepage
University of Maryland at College Park
Physics Department, Room 0220, (301) 405-8090