Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
ILUSTRATION OF A CONSTRUCTIVISTIC APPROACH TO TRANSFORM AND ASSESS THE TEACHING AND LEARNING PROCESS IN INTRODUCTORY PHYSICS MOISÉS ORENGO-AVILES University of Puerto Rico at Mayaguez Physics Department, PO Box 9016, Mayaguez, PR 00680-9016 [email protected] The behavior of falling objects was used to assess students’ misconceptions about acceleration and a think-pair-share constructivistic strategy was used in the classroom to promote the discovery of the underlying physical explanation. A set of 3 different questions were posed at the final examination to determined the gain in students understanding of the acceleration concept. The results and possible explanations for the discrepancies are explored in this article. Introduction Students commonly misinterpret the concept of rate of change and ratio, especially when they deal with the change of a rate of change as in the concept of acceleration. Acceleration is the result of a change in velocity, which in turn is the rate at which the position of an object changes. The traditional approach is to tell the students the definition or to pose it as a mathematical equation. The efficiency of the teaching by telling approach has been questioned [1] due to the fact that students’ previous experiences influence their understanding of the physical world around them. The behavior of falling objects was used to assess students’ misconceptions about acceleration and a think-pair-share constructivistic strategy that emphasized peer learning [2] was used to promote the discovery of the underlying physical explanation. The students where confronted in class with three questions. First they have to answer individually, and then revise their responses with their neighbor and finally the professor carried out the experiment and guided the discussion. This inquiry-based process was performed for each question, in sequential order. The questions and most common answers are summarized in Table 1. Results and discussion In order to illustrate that the direction of the acceleration for the object in questions 1 and 2 is always downward two methods were used. A vector diagram was drawn to represent the change in velocity and a numerical calculation stating the change in velocity as positive or a negative number. The direction of the acceleration is the same as that of the change in velocity, not that of the velocity. In the second case the direction of the change in velocity is the same as the direction of the velocity. To demonstrate that the acceleration at maximum height is not zero two more questions were posed. What is the velocity of the object at its maximum height? All the students agreed Table 1: Questions for falling objects Questions Think: Individual response Pair: Revised response Share: Response after experiment Discussion: Correct answered after discussion 1. A ball is thrown upward, after leaving the hand, what is the direction of the acceleration while it is moving up? Justify your answer. Out of 3 possibilities given (up, down, other) most of the students indicated up as the direction. Most of the students did not change their responses. But they supplied more justifications. The experiment consisted of throwing the object. Only a couple of students change their answer to the correct one. Acceleration points down. 2. A ball is thrown downward, after leaving the hand, what is the direction of the acceleration while it is moving down? Justify your answer. Out of 3 possibilities given (up, down, other) most of the students indicated down as the direction. Most of the students did not changed their responses. The experiment consisted of throwing the object. Only a couple of students change their answer to the correct one. Acceleration points down. 3. A ball is thrown upward, what is the acceleration when it reaches its maximum height? Justify your answer. All the students answered zero. None of the students changed their response. The object was thrown upward. None of the students changed their response. The correct answer is not zero. it was zero, which is the right answer. The second question was: does the velocity stay at zero after a second have passed? Of course not, the students agreed. Then the acceleration can’t be zero because this will imply constant velocity, but the velocity is zero, then the object will “float” there forever. The later is a contradiction, the experiment clearly shows that the object doesn’t stay “floating” at the maximum height it comes back to the ground. In conclusion, the acceleration for a falling object, no matter if it is moving up or down is always downward including when it is at the maximum height where the acceleration is not zero. In order to assess the students understanding of this basic behavior of falling objects, 3 different questions were posed in the final examination. The questions and the percentage of right answers are summarized in Table 2. Table 2: Final examination questions Questions Percentage of students with correct answer 1. A ball is thrown upward, after leaving the hand, draw the forces acting on the ball while it is moving up. 20% 2. A ball is thrown downward, after leaving the hand, draw the forces acting on the ball while it is moving down. 85% 3. A ball is thrown upward, draw the forces acting on the ball when it reaches its maximum height. 60% By the end of the course it have been illustrated that acceleration is due to a net force and the direction on the acceleration is that of the net force. Thus, it was expected that the students, knowing the behavior of the falling ball, were able to draw a unique force pointing downward for the 3 questions posed in the final examination. Based on the responses in the final examination the following misconceptions were identified: (1) when the ball is moving up there is a force pointing up, (2) when the ball is at the maximum height there is a force pointing up. The first misconception apparently comes from the idea that the force that was used (by the hand) to throw the ball up “stays” with it while the ball is rising. The force in the second misconception was identified as the normal force. The normal force is the reaction force of the surface acting on the object normal (perpendicular) to the surface, it only exist when there is a surface. The air might be mistaken as a surface, or the students got used to drawing a normal force in so many examples given in class. The other possibility is that they still think that the acceleration is zero at that point and they need a force to balance the weight so that no net force produced zero acceleration. Which is obviously wrong. These possible explanations need further analysis and exit interviews might help to elucidate the students reasoning. Acknowledgments The PR-CETP alliance was instrumental in providing stimulus and guidance through its evaluators and course revision specialists to explore this alternative way of teaching these concepts and others. Bio Moises Orengo-Aviles is Associate Professor of Physics and Science Coordinator for CETP at the Mayaguez Campus of the University of Puerto Rico. He collaborated in writing student centered activities in Physics for the K-12 PR-SSI (Systemic Statewide Initiative). He served as mentor for the LS-AMP (Louis Stoke Alliance for Minority Participation) to counsel student in pursuing graduate studies. He is coauthor of a handbook written in Spanish that promotes the used of cooperative learning at the university level. References [1] L.C. McDermott, Guest Comment: "How we teach and how students learn -- A mismatch?" Am. J. Phys.60 (4) 295 (1993). [2] Catherine H. Crouch and Eric Mazur, “Peer Instruction: Ten Years of Experience and Results”, Am. J. Phys. 69, 970-977 (2001)