PHY138 - Mechanics - Class 3 - Monday, September 19, 2005


About Your MasteringPhysics Mark

MasteringPhysics was designed to deliver homework assignments, and it does a superb job. However it was not designed for things like the Pre-Course Assessment Quiz, for which you get full credit for answering a question whether or not the answer was correct. It was also not designed to deliver two different types of assignments, such as our Pre-Class Quizzes and our Problem Sets.

Thus, as we discussed in class today, MP will show all your assignments as a single collection. Please trust us: at the end of the year we will re-calculate the marks for PHY138 as described in the marking scheme for the course. To remind you:

Just For Fun

In §2.6 the text concentrates on Galileo's description of free fall, but also briefly mentions the Aristotelian approach to this physical circumstance. Another idea about falling is available via the button to the right. It will appear in a separate window. Theory of Intelligent Falling

Problem Solving

Although we will emphasise concepts on the tests and exam, there will be some conventional algebraic and/or numeric problems too. The text develops a problem-solving strategy, beginning with the box on page 24, which it uses for every worked example.

We have prepared a one-page document on a small variation of the strategy in the text. You may access a pdf version of it with the button to the right; separate window. problem solving strategy

We will use this technique for every example we do in class, and strongly recommend that you use it for all problems that you do.

Today's Class

We finished Chapter 1 and almost finished Chapter 2.

I mentioned that the right answer (c) to the text's Stop To Think 2.2 is somewhat misleading. As shown in the text, the speed changes discontinuously at two times, which is physically impossible. The curve should be smooth at all points. I have contacted the author, Randy Knight, and this will be fixed in the next printing of the book. In fact, we added a fourth assumption about the nature of world according to classical physics: it is continuous.

We introduced the notation of integrals in class today. Note that the text sub-section A Little More Calculus: Integrals is explicitly excluded from the syllabus for the course. We know that most of you did not not do integration in high school, and also know that MAT135 will not get to this until January. In PHY138 we will be using integral signs as a short-hand for the infinite sum of rectangles under a curve to get the area, but will not ask you to know how to do the mathematics of integration until MAT135 catches up with us.

In-Class Question

We asked the In-Class Question accessible by clicking on button to the right. Virtually all students who answered got the correct answer: 3. in-class question

As usual for these questions, I may want to re-use it next year and so want to keep it between you and me. It will be available to you via the above link until after the Final Exam in the course, and I have disabled printing.

Class Materials

Flash animation extending Figure 1.22 (b) of the text. Theory of Intelligent Falling
Flash animation of a motion diagram. Theory of Intelligent Falling
Flash animation of the relation between position, speed and constant acceleration. Theory of Intelligent Falling
Flash animation introducing the integral sign. We only used the first "scene" of the animation. Theory of Intelligent Falling
Pdf version of the PowerPoint on the side screens. Theory of Intelligent Falling
Today's Journal. Theory of Intelligent Falling

Suggested Problems

Some students want to solve even more problems than those in the Problem Sets. This is not a bad idea: the more practice you get in solving problems the better you will get at it. Here are some suggestions:

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