Giancoli Chapter 6 Guide & Recommended Problems
From Eckerd Academic Wiki
In this chapter we will begin to do some major-league "skipping" of sections and parts of sections. Pay really close attention to this guide and to what I say in class. I want you to understand just a few specific things from this chapter.
Section 1: I want you to understand clearly the Law of Universal Gravitation (Eqn 6-1) and how to plug numbers into it. Also, that the "r" in the equation can usually be taken as the distance between the "centers of mass" of the two bodies in question. We will define the "center of mass" in Chapter 9; for now, just assume that it is the "center" of the body.
Section 2: contains nothing new. The gravitational force is just like any other force: it is a vector. If several forces (gravitational or otherwise) act on a mass, the vector sum is what is used in the second law of motion. This is not new.
Section 3: I want you to clearly understand the relationship between the Law of Universal Gravitation and the weight of an object. Specifically, Eqn. 6-4 is key. I will not stress the variation of "g" at different locations on earth, although those of you who are geophysics majors might want to read this closely - you'll likely see it again in some of your other courses.
Section 4: I'll do a little with satellites in class, and that is what you should know. There is nothing new in Section 4; we just combine the gravitational force law with the centripetal force formula from the previous chapter.
Section 5: is important for the history science - and not just physics. It was in trying to understand the motion of planets orbiting the sun that the scientific methodology was first formulated. "Kepler's laws" were empirical laws, that is, a summary of observational results without any attempt to explain why planets moved as they did. Newton's great breakthrough was to show that his universal gravitational law could be used (together with calculus, which he invented for the purpose) to demonstrate that Kepler's laws had to betrue. Not only that, Newton could then go on to predict new behavior, such as the motion of comets. Observation showed that his predictions were correct. This methodology of (1) observational results, (2) formation of a theory, (3) using the theory to predict new results, and (4) testing the prediction by further observation is what became the method used by allthe sciences. That is, the test of whether a field of study is or is not a science is whether they use the proper methodology. And this methodology was first used in a systematic way to understand planetary motion. I will want you to read this section, but will not emphasize very many of the "problems."
Section 6: is merely a definition, which we will not use. However, the concept of a "field" is important, and we will use it extensively later (beginning in Ch. 21) to talk about the electric force. Read this section, but there will be no problems assigned.
7. I will talk about Section 7, and will expect you to know the four "fundamental" forces by name, and to be able to write an intelligent sentence about each one stating how it differs from the others. No problems from this section will be assigned.
Section 8: is optional, and will not be officially covered in this course. If you have any interest in Relativity, I invite you to read these sections.
Recommended Questions and Problems for Chapter 6:
Questions: Q1 (yes, Mappleg, same), Q4, Q9(same, moon), Q14 (largest when acc up; least in free fall; same as ground when constant speed), Q21
Sections 6-1 through 6-3: P2, P3, P4, P5, P13
Section 6-4: None
Section 6-5: P38, P41
General Problems: P52, P60, P69, P70
