THE DIFFICULTIES STUDENTS FACE IN
PREDICTING THE OUTCOME OF AN EXPERIMENT
Athanasios Velentzas, Krystallia Halkia
School of Education, National and Kapodistrian University of Athens
Abstract: The present study attempts to detect secondary education students’ mental
processes when predicting the outcomes of Physics experiments in order to trace their
difficulties in predicting the results of experiments. The research sample consisted of
86 upper secondary-level students aged 16-17. Students had to predict the outcomes
of three Physics experiments and also to analytically express on an answer sheet the
“route” their thinking followed in reaching these outcomes. A qualitative content
analysis of the answer sheets followed.
The findings show that the “three I’s” (Intuition - Incompleteness – Irrelevancy)
typology of cognitive erring-mechanisms in thought experimentation can describe the
mental processes which lead students to fail when predicting the outcomes of Physics
experiments. Specifically:
- Intuition and everyday experience lead students to overlook or misrepresent school
knowledge,
- Students make incomplete assumptions. That is, they focus on only one parameter of
the “problem” - the most obvious one - and overlook others which could be critical for
predicting the outcome of an experiment.
- Students use irrelevant attributes of materials or irrelevant physics laws to predict
the outcomes of experiments.
Keywords: students’ predictions, Physics experiments, secondary education, school
lab work
INTRODUCTION
Practical work in the laboratory is of key importance in science instruction, since it
promotes the learning of science content and processes, as well as increases
understanding of the nature of science (Duit & Tesch 2010). However, while
laboratory work promotes competences in the skills of gathering information and
organizing observations, it has little effect on the acquisition of scientific knowledge
(White 1996). According to Millar (2004), it is unlikely that students could grasp new
scientific concepts or understand a theory as a result of any single practical task,
however well designed. The understanding of concepts and principles does not
“develop solely or predominantly from the experiment. The genesis of understanding
science is a cyclical process linking experiment and theory as well” (Duit & Tesch
2010, p.18). For this reason, students should have the opportunity to work “under
adult guidance”, and thus the role of the teacher is important (Vygotsky 1978, p.86).
If teachers aim to help students develop links between observations and ideas in an
experiment, they should first introduce these ideas, and it is “important that they are
‘in play’ during the practical activity” (Abrahams & Miller 2008).
A strategy which has been proposed to teach Physics by means of an experiment
(White & Gunstone 1992) has three steps: Prediction –Observation – Explanation
(POE). The present work is a pilot study limited to the first step of the above strategy
and attempts to trace students’ difficulties in predicting the outcomes of experiments.
In this step, it is crucial for students to “indicate both their prediction and the reasons
they have to support the prediction” (White & Gunstone 1992, p. 46). Thus, the
teacher would be aware of his/her students’ ideas and, in general, of their way of
thinking in order to help them to develop links between observations and ideas.
THE PREDICTION OF THE OUTCOME OF AN EXPERIMENT
The experimenter, when predicting an experiment’s outcome, “performs” the
experiment in his/her mind. Thus, we could suppose that the experimenter runs a kind
of thought experiment in his/her mind. According to Nersessian (1993), a thought
experiment, is a process of reasoning that “involves constructing and making
inferences from a mental simulation”. The experimenter constructs a dynamical model
in his/her mind, imagines a sequence of events and processes, and infers outcomes
(Nersessian 1993). In such a process, the student is forced “to access tacit intuitions,
explicit and implicit knowledge, and logical derivation strategies, and integrate these
into one working thought process” (Reiner & Burko 2003). If we adopt this
hypothesis, i.e. that the mental process when predicting a Physics experiment has
many similarities with the mental process when “performing” a thought experiment,
then the study of the factors that lead thought experiments to incorrect results could
help in understanding the barriers involved when students are asked to predict the
results of real experiments. By analyzing thought experiments proposed by well
known scientists, Reiner and Burko (2003) conclude that there are three cognitive
processes which may lead scientists to the wrong conclusion when performing TEs:
(i) Intuition: Intuitive judgment and past general experience may lead the
experimenter to override the conventional theoretical framework.
(ii) Incompleteness: The omission of the set of assumptions concerning the imaginary
world of a thought experiment may lead to erroneous conclusions.
(iii) Irrelevancy: Irrelevant assumptions that were included in the features of the
imaginary world in a thought experiment lead to logical conclusions that “may not be
relevant for natural phenomena.”
Similar cognitive processes “occur in naive physics learning” but naive learners
“replace theoretical constructs with intuitive knowledge” and “this replacement may
be much stronger for naive learners than for expert physicists” (Reiner and Burko
2003). Indeed, students tend to use their own ordinary common sense ideas rather than
any ideas from school science (Bliss 2008). Thus, “the three I’s” (Intuition Incompleteness – Irrelevancy) “provide a typology of cognitive erring-mechanisms
that can be used for predicting classes of errors in thought experiments, analysing
naive learning processes, and developing learning environments” (Reiner and Burko
2003). In the present pilot study, an effort was made to use the “three I’s” typology to
analyze students’ thinking processes when they predict the results of experiments. The
findings of the pilot study helped in the design of student interviews for the main
study which is in progress. A deeper understanding of the mental processes which
take place in students’ minds when they attempt to predict the outcome of an
experiment could help in designing teaching plans aimed at developing links between
practical work and school scientific knowledge.
METHODS
As mentioned above, the aim of present study is to detect secondary education
students’ mental processes when predicting the outcomes of Physics experiments in
order to trace their difficulties in predicting the results of experiments.
Three Physics experiments were selected, according to the following criteria:
(a) They refer to everyday phenomena because it is easier for students to express and
explain their views about things they experience, in contrast to unfamiliar situations.
(b) The necessary background knowledge for predicting the outcomes of these
experiments had been previously taught to students.
(c) Their outcomes contradict “common sense”.
Students had to predict the outcomes of the three experiments and also to analytically
express on an answer sheet the “route” their thinking followed in reaching these
outcomes. Specifically, students were asked mentally to compare:
- The value of the kinetic friction when a box moves onto a horizontal floor in two
situations: firstly, with its greatest surface in contact with the floor, and secondly, with
its smallest surface in contact with the floor (Figure 1 - Experiment 1).
- The time in which an ice cube melts when it is covered by (i) woolen fabric and (ii)
aluminum foil (Figure 1 - Experiment 2).
- The time of the free fall (from the same height) of two bodies with different masses
(Figure 1 - Experiment 3). Specifically, students had to predict the free fall of two
similar bottles which contained water, one of which was full, while the other
contained only a small quantity of water.
Experiment 1
Experiment 2
Experiment 3
Figure 1. The sketches used in the answer sheets, copied from the book
Διδάσκοντας Φυσικές Επιστήμες (Teaching Science) (Halkia 2012).
The research sample consisted of 86 upper secondary-level students (aged 16-17)
from a public school in Athens. A qualitative content analysis of the answer sheets
followed.
RESULTS
The findings of the qualitative content analysis of the students’ answers are presented
in Table1 and they are discussed in detail below.
Table 1
Students’ answers for each experiment. Number of students: 86
Experiment 1: Kinetic friction. Number of students: 25
Category Students
Students’ views
1.1
10
They claimed that the friction increases when the area of
contact between surfaces increases because “the number of
the points of contact between the surfaces” increases.
1.2
3
They recognized inertia and not friction as the critical factor
which prevents the box from sliding easily along the floor.
1.3
3
They claimed that they did an experiment on the spot (by
using their bag, a box or their sunglasses case) and they
experienced more friction when there was more area of
contact between the surfaces of the two bodies.
1.4
5
1.5
2
They just declared (without any explanation or by recalling
the relevant formula) that friction is independent of the area
of contact between surfaces.
They recalled the formula of kinetic friction but they said
that the friction coefficient depends on the area of contact
between surfaces.
1.6
2
Vague answers
Experiment 2: Melting ice cubes. Number of students: 36
Category Students
Students’ views
2.1
25
They claimed that the ice cube covered by woolen fabric
melts faster because the wool is hotter (or it “produces more
heat”) than the aluminum foil.
2.2
4
They recognized thickness or porosity as factors for thermal
conductivity and not the kind of the material used
2.3
4
They claimed that both ice cubes will melt simultaneously
because the cover does not play a role.
2.4
3
Vague answers
Experiment 3: Free fall. Number of students: 25
Category Students
Students’ views
3.1
14
They claimed that the heavier body falls faster because it is
attracted with a greater force by the Earth.
3.2
10
They claimed that the bodies fall simultaneously because “I
know it from physics class” or “we perform the relevant
experiment in physics class”. But, They do not give any
further explanation.
3.4
1
He claimed that the heavier body falls faster, since “I know
that all bodies fall with g, but the air resistance on the heavier
is smaller”.
It seems that the “three I’s” typology can describe the mental processes the students
follow when failing to predict the outcomes of the experiments. More analytically:
Intuition
Intuition and everyday experience lead students to overlook or misrepresent school
knowledge. As the findings in Table 1 show students
- assign incorrect attributes to materials. This confusion is due to the everyday uses
of the materials and students’ sensory experiences regarding them. For example, a
student (Experiment 2, category 2.1) wrote that “We use aluminum foil to maintain
the temperature of foods, while we use woolen gloves to heat our hands”.
- use school knowledge as décor and “pretext” in order to validate their intuition.
Indeed, in some cases, students do recall their school knowledge, but they
conveniently modify it to predict the outcome of the experiment in accordance with
their intuitive knowledge. For example, while students (Experiment 1, category 1.5)
recalled the mathematical formula of kinetic friction, they claimed that the friction
coefficient depends on the area of contact between surfaces, so as to support their
view that “more area of contact means more friction”. Also, in the cases of categories
1.4 and 3.2, students answered correctly by mechanically recalling their school
knowledge, but they could not support their predictions with meaningful explanations.
- “see” what they intuitively believe. Indeed, in the case of category 1.3, students
claimed that (in order to see if their spontaneous prediction was right) they actually
had done a similar experiment and they had found an outcome that was compatible
with their prediction! As White (1996 p.764) comments, “People holding different
beliefs will see different things…”.
Incompleteness
Students make incomplete assumptions when they are called upon to predict
phenomena. That is, students focus on one parameter of the “problem” - the most
obvious one - and overlook others which could be critical for predicting the outcome
of an experiment. For example, in the case of the Experiment 1 (category 1.1),
students take into consideration that the increase of the area of contact between the
surface of the box and the surface of the floor results in an increase of “the number of
the points of contact between the surfaces”, but at the same time they overlook the
decrease of the vertical (normal) force per unit of the area of contact. Also, students
(category 3.1) take into consideration that “more mass means more force of gravity”,
but they overlook the fact that more mass implies more inertia. It is worth mentioning
that students who predicted that the body B falls faster than the body A (Figure 2) also
claimed (Figure 3), that the two bodies travel equal distances per second. (This is a
finding from student interviews which took place in the context of the next phase of
the study, which is currently in progress.)
Β
Α
m
2m
Α
w
2w
Figure 2. Free fall
m
F
Β
2m
2F
Figure 3. Movement without friction
Irrelevancy
Students use irrelevant attributes of materials or irrelevant physics laws to predict the
outcomes of experiments (e.g. Experiment 2 - category 2.2 or Experiment 1 - category
1.2). In this case, the outcome of an experiment can be predicted correctly, but the
explanation is unacceptable because it is not generally applicable, i.e. it leads to
incorrect results in other situations. For example, in category 1.2 the result cannot be
predicted in the case where two bodies with different masses slide along different
surfaces (i.e. if the lighter body slides along a rougher surface than the heavier one).
DISCUSSION
When predicting the outcome of an experiment, students mentally simulate a kind of
experimental process. During the thought experimentation, students tend to use their
intuition and experience rather than logical reasoning (Reiner & Gilbert 2000). This is
the main factor - as the present study shows – which lead students to fail in predicting
the outcomes of the experiments and to justify their prediction. Specifically, the
findings of this study show that students, when predicting the outcomes of the
experiments assign incorrect attributes to materials, make incomplete or irrelevant
assumptions and basically use their intuition and everyday experience and not their
school knowledge. Also, it is worth mentioning that the students who correctly
predicted the result of an experiment by recalling the corresponding school knowledge
did not use a “meaning making” explanation. According to Hodson (1996), the basis
of a prediction is “some good understanding of the phenomenon or event under
consideration” and he suggests that “without theoretical understanding, predictions
are no more than ‘blind guesses’, and there is little of educational value in
encouraging children to make those”.
As the findings show, it is not easy for students to correlate their everyday experience
with scientific knowledge, and in this direction the contribution of the teacher is
decisive (Bruner 1985). According to Abrahams and Millar (2008), teachers should
devote a greater proportion of the lesson time to helping students use ideas associated
with the phenomena they have produced, rather than seeing the successful production
of the phenomenon as an end in itself. Hodson (1996) proposes a three-phase
approach for school science: modeling (the teacher presents this phase) – guided
practice (students work under their teacher’s guidance) – application (students work
independently of their teacher). Thus, the teacher should have a key role in practical
work which, apart from the designing of the “practical” performance of an
experiment, should involve the construction of an explanatory schema for helping
students to integrate the empirical data to a conceptual context compatible with the
scientific one. Such a schema could include:
(1) A model of the experimental apparatus. The teacher should provide an as simple as
possible representation of the “experimental devices” for two main reasons. First, to
reduce the “noise” in order to help students focus on the problem itself. For example,
in experiment 3, it would have been better to have used compact cubes than bottles
because some students integrated in their explanation the water or the air that were
contained in the bottles (e.g. “the one bottle contains more air and it may delay the
fall”). Second, to make it easy for students to quantitatively manipulate the parameters
of the problem. For example, students can easily mentally construct bodies of twice or
three times mass by using similar compact cubes.
(2) Prerequisite prοpositions relative to the attributes of the model’s elements, the
relations and laws concerning the phenomenon and the possible effect of the external
factors. The findings of the present study show that students (when predicting the
result of an experiment) assign incorrect attributes to materials and make incomplete
or irrelevant assumptions. Thus, it is crucial for learning by doing that the teacher and
students have classroom discussions to identify the propositions which are needed for
the prediction of the behavior of the physical system being studied.
(3) A process of logical reasoning. Students discuss the evolution of the phenomenon
based on the prerequisite propositions, and the teacher intervenes when it is needed.
(4) Conclusion. Students formulate their conclusions.
An example of an explanation schema (as a basis for a teaching plan) is proposed in
Table 2. The proposed schema is going to be implemented in the next phase of our
work, which is currently in progress.
Table 2
Explanation schema for the experiment of kinetic friction
Question
Model
Does the kinetic friction depend on the area of contact between the
surface of a body and the surface of the floor?
Five similar compact wooden cubes, A, B, C, D and E. The body BC
consists of the two cubes B and C glued together and the body DE
consists of the two cubes D and E glued together (Figure 4).
Prerequisite Attributes:
propositions (1) BC and DE are identical.
(2) All the surfaces of the cubes are identical.
(3) Weight BC or Weight DE = 2 · Weight A
Relations / Laws:
(4) Friction depends upon the nature of the surfaces in contact.
(5) Friction is proportional to the normal force; thus friction is
proportional to the weight of the body (because the floor is horizontal).
External factors:
(6) The resistance of the air is negligible.
(7) Experimental errors are not taken into consideration.
Process of
logical
reasoning
(a) Since the area of contact between the surface of body A and the
surface of the floor and between the surface of body BC and the surface
of the floor are the same, according to (2), (3), (4), (5), we conclude
that Friction BC = 2 · Friction A.
(b) D and A are identical, thus Friction D = Friction A
(c) E and A are identical, thus Friction E = Friction A
(d) From (b) and (c) we conclude that Friction DE = 2 · Friction A
(e) From (a) and (d) we conclude that Friction DE = Friction BC
Conclusion
From (1) and (e), we conclude that friction is independent of the area of
contact between the surface of a body and the surface of the floor.
Figure 4. Five identical cubes A, B, C, D, E
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