situation. For example, many students predict that a moving object emerging from a circular tube will continue in a circular trajectory once it emerges from the tube (rather than flying off in a straight line path), or they predict that a person running off a cliff will (as in a Wile E. Coyote cartoon) continue a short way off the cliff before abruptly falling straight down.

Although even young children, like adults, have an explicit concept of force that they use to explain what happens in different physical situations, the meaning of force is an intuitive one, very different from the mathematicized notion embodied in Newtonian mechanics. They tend to think of forces as active pushes or pulls that are needed to explain an object’s motion, rather than coming in interactive action-reaction pairs that are needed to explain not an object’s motion but its change in motion (acceleration). Thus, they see forces in situations in which a physicist has no need to postulate a force (e.g., when a coin is thrown upward, they postulate an upward force is imparted to the object from the hand for the duration of the upward trajectory to explain why it continues to go up), and they fail to see forces that are essential to a Newtonian analysis (e.g., many of the action-reaction pairs that are so central to a Newtonian analysis, such as the force exerted by a table on a book when it is resting on the table). They do not clearly distinguish between force and momentum, acceleration, position, and speed or between instantaneous and average velocity. In light of these findings, some have suggested that high school students may have an alternative naïve theory of motion, akin in many respects to historically naïve impetus views of the sort proposed by Aristotle or the medieval impetus theorists (Caramazza, McCloskey, and Green, 1981; Espinoza, 2005).

Others have argued that viewing these misconceptions as stemming from a highly coherent alternative impetus theory is misleading for several reasons (diSessa, 2004; Smith, diSessa, and Roschelle, 1993). First, it suggests that students are more consistent in their erroneous reasoning than they actually are. Although they may appeal to impetus notions in some tasks, they may not use them in other tasks in which they would be relevant. Second, it overlooks many other notions that students appeal to in their physical explanations, such as balancing, overcoming, or resisting. DiSessa argues that everyday physics is better thought of as exploiting a fairly large and diverse number of these low-level (often inarticulate) explanatory fragments that are evoked, often quite independently, in different contexts. Third, the naïve theories account overlooks many of the points at which students’ intuitions are actually in accord with mature physical analysis. For example, although students may not see the balance of forces in the situation of a book on a table, they do provide this analysis when analyzing a book on an outstretched hand. Thus, they are not as devoid of positive intuitions as the misconceptions literature would suggest. On this analysis there is much valuable knowledge, though admittedly often at an inarticulate subconceptual



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