Part 14A asked if the net force acting on the plane was zero. Question 19 gave a situation of constant speed under the effect of several forces - a person pushing a box at constant speed. In effect, Questions 13C, 14A and 19A were all based on equivalent situations - a body moving with constant speed. The number of students who answered correctly are shown in Table 3. An explanation for the variation in pretest results is that students have learnt to recognise the diagram used for Question 13C, that of a vehicle having four balanced forces moving at constant speed, and most answered using a rote-learned response.
Students learn to apply Newton's first law in similar contexts.
We suggest that, unlike Question 14A, fewer students had encountered the context for Question 19A and hence the context was treated by most with intuitive reasoning alone. Following use of Freebody , all students correctly answered 13C and there was an increase of 20 answering 14A correctly. It is likely that many of these students came to see that Questions 13C and 14A referred to identical situations. Many students held conflicting conceptions, both before and after use of the program. This is explainable if a conception is inextricably linked to a context and does not exist without a context in which it applies.