Physics for Closeted Aristotelians

Children aren’t empty vessels. They come to class with amusing, surprising and deep-rooted ideas, inconsistent with contemporary science. It is imperative for a teacher to recognise this and initiate a process of change as such ideas could hamper learning.

We grapple with physics every day, often without recognising the insights that established theories in this discipline provide to our understanding of day-to-day phenomena. Given the human tendency to rationalise, we tend to construct intuitive causal theories to understand and make predictions about the world around us. These intuitive theories are usually inconsistent with established scientific theories, leading to myriad misconceptions about physical phenomena.

One such misconception, around the concept of force, emerged from a discussion on projectile motion with 70 (20 boys & 50 girls) grade IX students of a government high school at Bairagarh Chichli, Bhopal, Madhya Pradesh.

Drawing out intuitive models of motion

The students were asked to predict the path a ball or marble would take if it were to be rolled off the edge of a table with a certain horizontal velocity (see Concept Builder: Motion under the influence of gravity). Only two students chose Option II, while the rest chose Option I.

In an effort to bring their underlying theories on motion to light, the students were invited to share the rationale for their predictions. Those who chose Option I reasoned that the force applied by the agent to push the ball from the table would be transferred to the ball. As a result, the ball would continue to move in the same direction (~ a straight line) till this force became weak enough to have no effect on the ball’s motion. At this point, gravity would start acting on the ball, pulling it down. This seemingly logical explanation is not new — it has a lot in common with the impetus theory of motion (see Box 1). In contrast, the two boys who chose Option II explained that their response was based on the positions they were most likely to take to field a catch in their daily game of cricket.

One way of getting learners to question the validity of their mental models is to provoke some cognitive dissonance by offering counter-examples. Thus, students from both groups were encouraged to test their predictions before the next class. To identify any change in their existing cognitive schemas, even if only at the peripheral level, students were given the choice of revising their responses. 

Testing intuitive models of motion
When discussion around the experiment was resumed in the next class, both groups continued to stand by their earlier choices. However, the first group (of closeted Aristotelians) suggested that the path of the ball in Option I be modified to reduce the length of its linear portion (see Box 2).
It is likely that on trying this experiment out, the students who’d chosen Option I had noticed that the ball or marble they’d launched did not show such a prominent horizontal path. This was reflected in their attempt to tweak their intuitive model (to accommodate the anomalous observation) instead of rejecting it entirely.  Consequently, their ideas about motion remained fairly consistent with those of the impetus theory and reflected certain elements of Albert of Saxony’s model for projectile motion. 
In order to provoke students to question the validity of their preferred mental model of motion, the class was encouraged to set-up a practical demonstration of the experiment. This led to a discussion on method — how would the path (I or II) of a marble to point B be determined? One of the students recommended creating a video since the marble's speed may cause its path to remain imperceptible to the naked eye. Although he could not verbalize what he wished to do with the video, the other students agreed to try this method out.
Prior to the next class, the instructor shot many videos of marbles with different horizontal velocities being rolled off the edge of a table. These videos were shot at a relatively high frame rate (i.e., in slow motion) so as to allow viewers to trace the path of the marble. When these videos were projected on the blackboard, the students argued that if a marble were really to move at the sluggish pace seen in the videos, it would simply topple off the edge of the table. Re-iterating that the videos had been shot in slow motion seemed to make no difference to student views on the motion of the marble. To remedy this, the students were encouraged to record their own videos of the marble’s path, and use these to make sense of how a slow-motion video depicts things occurring in real-time.
Once the student-shot videos were ready, the instructor used their projections on the blackboard to trace the path of the projectile. A marble seemed to take ~400 milliseconds to hit the ground. Given the marble’s negligible vertical velocity, no appreciable vertical displacement was observed within the first few milliseconds of its leaving the table. The students continued to interpret this as evidence that the marble moved in a straight line, albeit for a much smaller amount of time than in their original prediction. This seems to suggest that even when faced with scenarios that present information or evidence inconsistent with their intuitive theories, children may tend to focus on those elements of the scenario that seem vaguely consistent with these theories. This tendency can be explained through two facts — we are cognitive misers, and processing familiar information requires a smaller cognitive effort than that required for processing new information.
Once it was established that the marble took a curved path, some students voiced their concerns regarding the demonstration. They asserted that it was because the marble was round in shape that it took a curved path. A cuboidal object would take the path depicted in Option I; a sharpener with both square and circular edges would take the path depicted in Option II; and an irregular object would take an irregular path. The instructor asked the children to test their assertion by using slow motion videos to record the launch of each of these objects. This new batch of videos was projected on the blackboard, and students were invited to trace the trajectories of each of these different objects. This exercise proved beyond doubt that the shape of the objects did not alter its trajectory. However, the belief that objects continue to move in a straight line after breaking contact with the table seemed to remain more or less unaltered for students who started out with such a preconception.
Teaching reflections
At a programme level, it may be worth considering why Newtonian ideas on motion are introduced only in high school. Why are students given so much time to form their own ideas and theories about motion before there is any curricular intervention to address them? Then, over a course of the 2-3 years of secondary and higher secondary schooling, the student is expected to shun her beliefs and accept what the textbook presents as ‘correct knowledge’. Research shows that older children may be less flexible (sometimes, even less interested) than younger children in altering their mental models, suggesting that it may be better to catch them young (see Box 3). This does not discount the difficulties of making such concepts intelligible, plausible, and useful for young children. 
At the curricular level, it may be useful to re-consider the sequencing of topics in mechanics in science textbooks (see Box 4). Students are first taught about motion in kinematics without learning its causes (or the manner in which forces influence motion). They study acceleration as a mathematical quantity without having insights into its causes or physical implications. It is only when the topic on forces is introduced do they get a taste of the causes of acceleration. Till that time, they are left alone with own imagination about the causes of motion. Is this what leads them to seek various common sense and intuitive ideas about different phenomenon?
Pedagogically, folk theories may be best addressed by devising exercises that help students become ‘acutely aware of their misconceptions’.1 Getting students to verbalize or pictorially depict the models they have of a particular phenomenon may help teachers understand the specific nature of their folk theories. This can be used to plan an intervention that introduces the concept in an intelligible, coherent (internally consistent), plausible (not irreconcilable with the child’s other world views) and fruitful (more useful than the older viewpoint) manner.4

To conclude

Here’s another exercise for the physics educator:

 A person holds one end of a string in her hand. A mass is tied to the other end. The person starts rotating the mass  along a horizontal plane. What path would the mass take once the person lets go of the string?

 How would you respond to this question? Pose this question to your students, and seek their responses. If quite a few responses turn out to be folk myths, can you think of an experiment or a pedagogical strategy that counters it?



  1. Chick, H., & Vincent, J. (Eds.). (2005). Proceedings of the 29th Conference of the International Group for the Psychology of Mathematics Education, 4: 97-104.
  2. Halloun, I. A., & Hestenes, D. (1998). ‘Common sense concepts about motion’. American Journal of Physics, 53(11): 1056-1065.
  3. McCloskey, M. (1983, April). ‘Intuitive Physics’. Scientific American: 122-131.
  4. Osbourne, R. (1991). ‘Building on Children's Intuitive Ideas’. In R. Osbourne, P. Freyberg, B. Bell, R. Tasker, M. Cosgrove, B. Schollum, R. Osbourne, & P. Freyberg (Eds.), Learning in Science: 41-50.

Nitish Sehgal works with Samavesh in their Science Education Project. He is an electrical engineer with a keen interest in physics education. He loves to teach, and wants to make science education interesting and useful for students. He is a travel and music aficionado as well as an almost autodidact guitar player.

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