DB5 - Collision? What Collision?
Investigating Student Difficulty With Identifying Collisions
Based on a talk given at the AAPT Summer Meeting in San Antonio, TX, on
August 6, 1999 in session DB.
by Dave Van Domelen
The Ohio State
Supported in part by NSF Grants DUE9396205 and GER9553460
Outline? What Outline?
I. The PDD - The Problem Decomposition Diagnostic
II. The Background - How the PDD was administered.
III. The Items - PDD items involving collisions.
IV. The Results - What the students did.
I. The Problem Decomposition Diagnostic
The Problem Decomposition Diagnostic, or PDD, is an instrument being
developed at the Ohio State University. It is intended to examine the
ability of students to:
The PDD was administered to a number of small groups before being given to
classes in Autumn 1998. The data presented in this talk concern only the
first aspect of the test, specifically student ability to identify collision
- Break multi-part mechanics problems into sub-problems that they are better
able to solve.
- Identify student approaches to solving these sub-problems.
During Autumn Quarter 1998 at The Ohio State Unversity, three groups of
students were tested using the Problem Decomposition Diagnostic. All three
were taking some version of PHYS 131, the introductory calculus-based
All students in H131 and 131E were tested. Due to scheduling constraints
(specifically, finding time to administer both the PDD and the FCI),
not all students in 131 were tested.
- "Regular" Calculus-based physics course: PHYS 131 (N = 52)
- Honors 131 for Physics Majors: PHYS H131 (N = 41)
- Honors 131 for Engineering Majors (Gateway): PHYS 131E (N = 93)
III. The Items
Two items on the PDD were designed with collisions as part of them. The
first was the "Pendulum Box Bash," where a pendulum swings down and strikes a
box, which then slides along a table until stopped by friction. Students
were presented with the simplified version in which the pendulum stops after
hitting the box:
The second item was a "Block Catcher" in which a block slid along a
frictionless surface until it hit another block attached to a spring. The
two blocks would stick together and the spring would be compressed:
Student Exposure To Items
The regular 131 students performed a lab using the Pendulum Box Bash setup
seen in Collision One. They worked in groups to solve the problem, and had
their work assessed by the lab instructor. They had no special exposure to a
Block Catcher problem.
Honors H131 students had no specific exposure to collisions in either
context, Pendulum Box Bash or Block Catcher.
Gateway 131E students had no specific exposure to either setup. However,
they did receive treatment regarding internal energy conservation in
collisions, using a variety of demos applied by Xueli Zou during Large Group
meetings. Poster BK33 by Xueli Zou at the San Antonio meeting covered this
Criteria For Success
Before scoring the students on performance, it was
necessary to determine what constituted a correct response. The following
criteria were established:
The second criterion turned out to be redundant in this case, as all students
who met the first criterion also met the second. It is worth noting that
this is a very lenient scoring scheme. The intention was to mark as wrong
only those responses which were clearly wrong, beyond reasonable doubt. As a
result the percentages which will be reported later in this paper are likely
to be greater than the "real" percentage of the students who would have
identified the collision. In addition, because many students would not have
broken the problem up without being told to do so, there is an additional
group of potential "false positives."
- The student's test sheet must contain a response that indicates something
was happening at the time of the collision. In other words, the student must
identify a sub-problem that could potentially be the collision.
- The student's classification of the sub-problem could not rule out the
possibility that the student saw the sub-problem as a collision.
As you can see, the regular and honors physics classes have virtually
identical performance in both collisions. Oddly, performance overall was
poorer on the obviously inelastic collision than on the partially elastic
collision, a result that suggests further research is needed on student
concepts of collisions.
Most dramatic, of course, is that a rather minor treatment (only about an
hour of contact time or less) produced large improvements in student
performance. One possibility is that once a student recognizes what's going
on in a collision, they're more likely to recognize a collision as a
In classes without specific instruction, students may not view collisions as
important parts of a complex problem. This may lie in an assumption that
kinetic energy is conserved.
Even limited treatment (see poster BK33) can be very effective in reducing
student difficulty in recognizing the relevance of collisions.