HOW PRE-SERVICE PHYSICS TEACHERS INTERPRET STATIC AND KINETIC
FRICTION: A LABORATORY EXPERIMENT
Ozlem Oktay1,* and Derya Kaltakci2,**
1
Department of Secondary Science/Math. Education, Middle East Technical University, Ankara, Turkey,
ozoktay@metu.edu.tr
2
Department of Secondary Science/Math. Education, , Middle East Technical University, Ankara, Turkey,
kaderya@metu.edu.tr
Abstract
The aim of this study is to explore pre-service physics teachers’ conceptual understanding and
their reasoning underlying a physics topic. Friction was chosen as a concept. Data were
collected in an elective laboratory course designed for ten pre-service physics teachers at
Middle East Technical University (METU) in Turkey. At the beginning of the laboratory
course, a brief pre-test was given to the pre-service physics teachers. The purpose of the pretest was to search their preconceptions about the friction forces (static and kinetic), net force
and applied force, acceleration and Newton’s second law of motion. For this experiment, a
worksheet was prepared by modifying the related topic from Physics by Inquiry (McDermott,
1996). The entire process was video recorded for data analysis. In addition, pre-service
physics teachers’ written works on the experiment were used for analyzing their conceptions
on the topic. At the end of the work, a feedback questionnaire was given to investigate preservice physics teachers’ attitudes towards the experiments. Qualitative analysis of data
showed that pre-service physics teachers, even though they are capable of using equations
related to static and kinetic friction, are lack of conceptual understanding on the topic. Also,
they had positive attitude toward the instructional process.
Introduction
Physics education research has been emphasized on students’ difficulties and misconceptions
(Hammer, 2000). If they do not have any clear and informed conceptions about some topics,
they cannot construct their own learning and meaningful understanding. In this study, concept
of friction was chosen as a laboratory activity. Because, most of the time this concept is
experienced in our daily lives. It is given as a concept in high school curricula and
introductory physics university courses. Also, it is covered under the heading of ‘‘Force and
Motion’’. Although, most of the tasks required the basic mathematical formulas can be solved
related to this concept, students have inadequate understandings and applications problems in
connection with Newton’s law of motion. In addition, we chose this topic if students think
that this topic is useful and mostly related to the real life experiences, they can improve their
motivation and effort to their lesson (Barlia & Beeth, 1999; Pintrich & Schunk, 1996). Our
aim is to give critical reflection taking into account pre-service physics teachers’
understandings and attitudes and to investigate common student difficulties and problems
about this concept.
* On behalf of Department of Secondary Science/Math. Education, Ataturk University, Erzurum, Turkey
**On behalf of Department of Secondary Science/Math. Education, Kocaeli University, Kocaeli, Turkey
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These research questions were investigated;
(1) What are the common misconceptions and difficulties related to the force of friction?
(2) How do pre-service physics’ teachers explain the force of friction and factors that
affected to this concept?
(3) How do pre-service physics’ teachers explain the Newton’s second law of motion
considering the force of friction?
(4) What are pre-service physics teachers’ opinions about the topic and the laboratory
activity?
Related Literature
Researchers from different theoretical perspectives argued that the most important things that
students’ bring to their classes are their concepts (Griffiths & Preston, 1992). For this reason
studies on students’ conceptions and misconceptions along with their reasoning are of
particular interest to educators and researchers in that field. Studies in students’ conceptions
and reasoning about the force concept (Clement, 1982; Halloun & Hestenes, 1985) have been
studied widely in physics education. In the scope of the force, friction is a concept that needs
some further investigation.
Some studies have been investigated students’ specific difficulties with friction (Krim, 2002;
Besson, 2004). Generally, in these researches as a misunderstanding, students do not think
that friction forces as a motive role as well as a resistive. Another research conducted by
Viennot (2002) proposed a short teaching sequence based on different models. She examined
students’ common concepts becoming guidance in the modeling process by designing lessons.
Another research is conducted by Corpuz and Rebello (2006) studied microscopic friction by
investigating university students’ mental models.
Based on the literature review, it seems that the friction concept has a key role to investigate
on different situations. In main mechanics concepts such as force, friction is needed to be
conceptualized by students.
Methodology
In this study, qualitative research methodology was used to gain an insight about the
phenomena.
Sampling and Fieldwork
The participants of the study were ten pre-service physics teachers at Middle East Technical
University (METU) who take Laboratory Experiments in Physics Teaching course. Study was
conducted with a total of five groups. In this study, as a teaching method inquiry process was
used. The inquiry process was used in order to examine pre-service physics teachers’
reasoning and improve the pre-service physics teachers’ conceptual understanding by
generating discussion environment in the laboratory. During the laboratory work, the preservice physics teachers were required to evaluate the whole experimental process and
interpret their findings. During the whole process two researchers were included into the
course. Their role was guiding the inquiry process and collecting data.
Data Collection
Video records, individual interviews, written works, a brief pre-test and feedback
questionnaire were used in order to get deep information about conceptions and reasoning
about the concept.
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At the beginning of the laboratory course, a pre-test was given to the pre-service physics
teachers so as to search their preconceptions about the friction forces (static and kinetic), net
force and applied force, acceleration and Newton’s second law of motion. It included one
question composed with four parts. For this experiment, a worksheet was used by modifying
the related topic from Physics by Inquiry (McDermott, 1996). It consisted of two parts. In part
one, we asked pre service physics teachers to examine static and kinetic friction force for
different types of sliding surfaces, different masses and different sides of the same object.
They analyzed the factors which affect the friction force and distinguish static and kinetic
friction forces. We asked pre-service teachers’ to write reasons and explain each situation. In
the second part, the participants performed a basic Newton’s second law of motion
experiment in which they observed the motion, took data, plotted graphs and interpreted them
considering the friction forces. Researchers were conducted twenty-minutes of semistructured individual interviews with participants at the end of the course. It provided a
validation of written works. In addition, pre-service physics teachers’ written works on the
experiment were used for analyzing their conceptions on the topic. At the end of the work,
feedback likert type questionnaire was given to investigate their attitudes towards the
experiments. It included ten statements from strongly disagree to strongly agree as well as an
open ended item for any suggestions and opinions about the experiments.
Findings
Pretest
In the pretest pre-service physics teachers were asked a three-level question that was revised
from Physics by Inquiry (McDermott, 1996). The pretest question is given in Figure 1. For the
question, only four of the ten participants draw a qualitative graph with considering the
friction force and starting the graphs from a nonzero applied force by the spring in zero
acceleration. Also there are different reasoning for the slopes and acceleration of the block on
wood and ice surfaces. Table 1 illustrates some examples for the participants’ answer.
Figure 1. Pretest Question for the Study
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Table 1. Examples to Student Responses for Pretest Question
Icy surface
Wood surface
Student 1
If applied force is more
than friction force block
gains
a
constant
acceleration and if we
increase
force,
acceleration increases too.
The starting force will increase
and the slope of line will
decrease since friction is greater
( awood < aice).
Student 2
Acceleration
increases
with the increasing force.
The graph starts from fo
since there is a small
friction
and
no
acceleration until the
force exceeds the friction.
Friction will be greater fo’ and
the acceleration for the same
force will be lower. The lines on
the graph must be parallel, since
due to friction there will be no
force
relates
with
same
acceleration for both graph, it
will never intercepts.
Student 3
F/a=m, since the tangent
of the graph , mass, will
be constant the graph
should be linear.
The graph does not change,
since the slope of the plot yields
the mass of the block, which is
same for the two cases.
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Student 4
Acceleration increases as
the force increases.
On wood surface acceleration
decreases. But F is also
decrease. So the plot of the
graph does not change.
Student 5
If force exceeds friction it
accelerates
constantly,
otherwise
it
won’t
accelerate and stay at rest.
If force exceeds friction it
accelerates
constantly,
otherwise it won’t accelerate
and stay at rest.
Student 6
For different constant
forces we obtain different
accelerations.
In this case there is bigger
friction, so line will shift to left.
It means with same applied
force, we obtain smaller
acceleration.
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Written Work and Individual Interviews
This part included two parts. We prepared this worksheet revising from Physics by Inquiry
(McDermott, 1996). We were considered to point out static and kinetic friction force and
some factors that affect the friction. Teacher candidates tried some procedures by using
different type of surfaces (glass, Styrofoam, marble, cardboard, carpet, etc.), different masses
of blocks and different sides of same objects.
When we look at the individual interviews and video records, they were familiar with basic
concepts about the friction force, the difference between static and kinetic friction, and factors
that needs to be investigated in the worksheet. But, they experienced some confusion about
their results of the surface area of the same object which is in contact with the surface. They
did not much more reliable and dependable results in this section. All of the students’ prior
ideas and all information in the written books explain surface area of contact of sliding
surfaces has no influence on friction. When pre-service teachers had this trouble with what
they know before, they tried to explain by changing different conditions as if they are a
teacher. Firstly, they did not notice to consider at microscopic level and surface phenomena.
Later in the interview part with the probing questions, they discussed the nature of materials
in contact and their surface coatings can be different, and can cause differences friction force.
In the second part, a question was asked as indicated in Figure 2. With this question, we
investigated how they interpret Fapplied, Fnet forces, friction force, starting point of the line, the
value of x and y intercept on their graph. Table 2 illustrates some examples and participants’
answer.
Obtain a cart, a heavy block, and a dynamometer from. Locate a smooth surface, approximately four
meters long, on which you can roll the cart. Mark starting and finishing lines three meters apart on the
surface. Place the heavy block on the cart. We will refer to the cart plus the heavy block as the “cart
system.” Attach the dynamometer to the cart system using about 1 m of string.
A. Practice pulling the cart system, initially at rest, between the starting and finishing lines using the
dynamometer to exert a constant force throughout the motion.
B. Select a particular constant force and record the time that it takes for the cart system, starting from
rest, to travel three meters. Repeat this measurement at least four times and average your results.
Calculate the acceleration of the cart system.
Figure 2. Main question in Part 2
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According to results, all of the pre-service physics’ teachers indicated that Newton’s second
law which is the acceleration of an object is directly proportional to the resultant force acting
on it and inversely proportional to its mass. But, out of ten participants as seen above had
some problems related to pulling force and resultant force. They were not aware of the
friction force when drawing their prediction graph in this situation. The other five of the
participants stated that F is proportional a, but graph do not start from zero point, because of
the friction force. After giving the prepared data, they asked to draw plot of graph F versus a.
Then they compared their predicted graph to the plotted from the data. Then they discussed
the value of x and y intercepts, since none of the participants mentioned it in their worksheets
in detail. An example is given above.
I: What is the value of the y-intercept (x=0), what do you think?
S: Hımm,
I: Think about the acceleration in this point.
S: a=0. So according to Newton’s first law, if an object at rest it will remain at rest or if an
object in motion, will continue in motion with a constant velocity.
I: So at that point which condition can be appropriate according to Newton’s first law?
S: We pulled this card system with a constant force, so it cannot be at rest at this point. It
might be in motion.
I: Now we said that at this point acceleration is zero, what about the time? Is it zero?
S: No, time cannot be zero at this point. It can be any time. So before and after that point the
object is in motion, at that time it has zero acceleration. This point must be the place where
card system is moving with constant velocity.
I: What about the force at that point?
S: Fnet is zero. Pulling force should equal to friction force.
I: Is this static or kinetic friction?
S: I think it is a kinetic friction force, because we said there is a motion. So this can be kinetic
friction.
I: Ok. Let’s think about the x-intercept. Before this, if you extent the line, you see that it does
not intersect at (0,0) point.
S: We learned that it was friction force so, line do not intersect at (0, 0) point.
I: Ok. What about the value of x-intercept?
S: This value is negative. Yes, line passed from a value at negative x-axis. It shows a negative
acceleration in the opposite direction force.
I: Good. How can you describe this motion of the cart?
S: Hmm, good question. Pulling cart has a positive acceleration before, and then the rope
might be broken and it decelerates.
Feedback Questionnaire
The results of the feedback questionnaire showed that pre-service physics teachers’ had a
positive attitude toward the instructional process. According to the results of the
questionnaire, pre-service physics teachers found the topic in the instructional material
interesting and at an appropriate level. They also claimed that the experiments helped them to
come up with ideas that they had never thought before. Some pre-service teachers stated that
the x-intercept in F versus a graph is a challenging and thought-provoking part of the activity
that they never thought before.
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Conclusion and Discussion
As indicated before, our purpose was to investigate pre-service physics teachers’ conceptual
understanding and their reasoning skills on friction concept that is one of the important topics
of physics. With the inquiry process integrated into laboratory experiment showed that preservice physics’ teachers although they explain and know the basic concept about the friction,
sometimes they had some difficulties. For example, most of them did not interpret the graphs
of applied force versus acceleration and net force versus acceleration. They had different
reasoning about the starting point of the graphs and the value of x and y intercepts. On the
other hand, all of them explained the difference between the kinetic and static friction, and
factors affecting friction. Sometimes, they took some unreliable numerical results. As a
reason, they ignored to take data at least three times. They did not notice to consider at
microscopic level and surface phenomena. During the challenging questions in the inquiry
process, they discussed the nature of materials in contact and their surface coatings can be
different, and can cause differences friction force. Another point in this study, pre-service
physics teachers’ had a positive attitude toward the instructional process. They also claimed
that the experiments in the worksheet challenged them to re-think critically. We can say that
pre-service physics’ teachers were not familiar inquiry as a method in the learning and
teaching. Prepared worksheets and appropriate guidance by instructors helped them to think
more critically and explore their reasoning. Therefore, the findings of this study could help
instructors in order to use kinds of approaches and student- centered activities when teaching
the concepts in physics.
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