Instructors_Guide_Ch12 - 12 Newtons Theory of Gravity...

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12 Newton’s Theory of Gravity Recommended class days: 2 Background Information Although satellite motion and celestial mechanics are somewhat peripheral to the text’s primary focus on the physics of earthly objects, this chapter does contribute to the overall coherence of the text. The Newtonian synthesis that united earthly and heavenly motions was an important historical event that propelled physics into the forefront of the developing modern worldview. Some attention to these issues helps to unify and conclude several strands of thought that have been developed in Part I and Part II. In addition, Newton’s law of gravity and the physics of planetary orbits will reappear as models for Coulomb’s law and for Rutherford’s planetary atom. Although superseded by quantum mechanics, the Rutherford atom is an important stepping stone on the road to understanding atomic structure. This chapter provides an opportunity to spiral back to several points of conceptual difficulty and to give students an opportunity to reinforce their understanding. These include: • Difficulties with circular motion. • Difficulties understanding and using energy conservation. • Difficulties interpreting energy diagrams. Some instructors like to introduce gravitational fields and even Coulomb’s law at this time. Although sympathetic to the idea, I’ve found that this approach does not work. Most students have major conceptual difficulties with the idea of charge and with the properties of charges, and a large effort will be made in Part VI to deal with these difficulties. In addition, students have an excep- tionally difficult time with the concept of a field . Fields are very abstract and intangible entities, and another major effort will be required for students to understand and use the field model of interactions. Until these issues are dealt with, simply defining “the force between charges” and “the gravitational field” is a hollow exercise, devoid of any connection to physical phenomena or situations. Students can memorize the definitions, but few have any idea what they mean or how to apply the information. Consequently, I’ve found it advantageous to defer charges and fields until there is adequate time to develop the concepts. Note that this chapter is entitled the
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This note was uploaded on 01/14/2011 for the course CD 254 taught by Professor Kant during the Spring '10 term at Central Oregon Community College.

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Instructors_Guide_Ch12 - 12 Newtons Theory of Gravity...

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