Analogues Concepts and Parallelism in High School PhysicsAfter reading the article “Using Gravitational Analogies to Introduce Elementary Electric Field Theory Concepts” by Susan Saeli and Dan Maclsaac (1) I thought I would like to share a few suggestions from my teaching practice about applying such analogies to a high school physics curriculum.Experience and ConclusionsI had been using similar analogies in my physics 1 and AP physics classes for a few years. However, at one point I realized that I needed to modify the way I introduced them to students. My observation was following: - Although such analogies were a great educational tool, students seemed to have been rather overwhelmed by being shown them. I had the impression that students viewed these analogies as a new knowledge than a tool helping them comprehend new concepts.This observation resulted in some modifications of the method. The main conclusions were following:- Analogies will serve their purpose well if the concepts to which they refer are taught or emphasized strongly enough in the section from which they originate. In other words; if section A is to be used as an analogy to teach section B, then the section A must contain all the types of concepts that section B does.- Students need to practice certain analogues types of problems in order to retain the previous knowledge and exercise correlation to new concepts.An analysis of a typical high school physics curriculum shows that there is much more emphasis on electrostatic fields and forces than on their gravitational counterparts. For a reference, I summarized topics outlined in AP Physics B curriculum related to forces and fields in both sections; Gravitation and Electrostatics.Table 1: Summary of correlated topicsGravitation Electrostatics- Determine the force that one spherically symmetrical mass exerts on another- Determine the force that acts between specific point charges - Calculate the magnitude and direction of the force on a positive or negative test charge- Calculate the net force on a collection of charges in an electric field- Determine the strength of the gravitational field at a specific point outside a spherically symmetrical mass- Describe the electric field of a single point charge- Use vector addition to determine the electric field produced by two or more point charges. - Define electric field in terms of the force on a test chargeComparing both types of fields and forces, one can notice that Gravitation does not contain manyof the detailed concepts that students are expected to learn in Electrostatics. Similar conclusioncan be drawn by comparing Potentials and Potential Energies in both sections of AP Physics B curriculum or in any other physics courses.My main “lesson” was that if certain concepts are to be presented as analogues, they need to be emphasized and learned by students in the first place.How to strengthen the parallelism between Gravitation and Electrostatics? It is apparent that the purpose of teaching physics is not exposing students to analogies but teaching them the content of the subject. The question that I tried to find an answer for was; can Imake some modifications to my high school physics curriculum to balance the contents of both sections? Here is what I came up: - The parallelisms can be much more effective and electrostatic fields can be better comprehended by students if additional types of questions are introduced in the section ofgravity.- While teaching gravity, students need to be informed that similar concepts will be studiedin the section of electrostatics. This proactive approach will prepare them for considering electrostatics as another application of already learned general physics concepts.Below is a sample of a modified section of gravity referring specifically to the superposition principle. The modifications refer to enriching types of questions rather than implementing new concepts to the curriculum.Table 2. Proposal of modified curriculumConcepts Physics 1 AP PhysicsGravitational force acting on a specific object due to other masses.Masses are arranged along astraight lineMasses are arranged at corners of a square or otherregular polygonIntensity of gravitation fieldat a specific location due to more than one object.Masses are arranged along astraight line and the vector of intensity of gravitation field is found at a specific location along a straight lineMasses are arranged at corners of a square or otherregular polygon and vector of field is calculated at a given locationA respective modification can be created for gravitational potential energy and gravitational potentials as well as for other sections.Below are samples of analogues problems that students might be assigned while studying gravitation fields. These problems correlate to the suggested above modifications.Example of a problem for physics 1Two masses arranged as shown below are placed in space where no other external gravitational field exists. a. Calculate the net gravitation field at the point K due to these masses. b. If an additional mass of 5 kg is placed at the point K, calculate the gravitational force exerted on the mass due this net field.Example of a problem for AP PhysicsTwo masses arranged as shown below are placed in space where no other external gravitational field exists.a. Calculate the direction and magnitude of the net gravitational field due to the masses at the location where the axes intersect (0, 0).b. If a mass of 1 kg is placed at (0, 0), calculate the magnitude and direction of the instantaneous acceleration of the mass.The above problem can be reassigned in the section of electrostatics with masses replaced by charges. Another possible extension of this modification can be created by combining electrostatic and gravitational fields and asking students to predict the action of the fields on an additional mass and on a charged object. SummaryI think that any approach that makes physics concepts more concise and integrated is worth to betried in classroom. With the small modifications made, analogies make more sense to students and their understanding of electrostatics has been much more solid since then.References1. Susan Saeli and Dan Maclsaac, Using Gravitational Analogies to Introduce Elementary Electric Field Theory Concepts. The Physics Teacher February 2007.2. 2006 AP Annual Conference, Lake Buena Vista, FL, Professional Development Workshop Materials, College
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