PHY138 - Mechanics - Class 3 - Monday, September 18, 2006


"If I have seen further than others, it is by standing on the shoulders of giants."

-- Newton


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

In-Class Questions

We asked three questions in class about significant figures. Here is a pdf of the questions we asked; separate window.

Most of the class got these questions correct( 80%, 80% and 75% respectively). The rest of the class should carefully review the material in §1.9: this subject is required for some MasteringPhysics problems.

As part of the discussion, we talked about how the potential amgibuity in these questions, particularly the second and third one, is resolved if one writes the numbers in scientific notation.

On Wednesday November 1, Dr. Harlow and I will re-visit this topic with significantly more sophistication than the text's discussion of this topic.

Other Class Materials

Here is a pdf of the PowerPoint on the SideScreens. Accessible via the blue button to the right; separate window.
We showed a Flash animation illustrating the difference between displacement and distance. Accessible via the blue button to the right; separate window.
We extended the textbook's Figure 1.22 (b) with this Flash animation This was the second extension to the text's discussion of Motion Diagrams in §1.6. It is intended to show the power of this visualisation technique. Theory of Intelligent Falling
Here is today's Journal in pdf format. A couple of students pointed out that I seem to have punched the wrong numbers on my calculator for the example. The corrected version appears in purple in the journal. Thanks to those students who pointed out the mistake. 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:

I chose these problems basically because in some sense I like them. I don't pay any attention to whether they are odd-numbered, for which the answers are in the back of the textbook, or are even numbered. Your tutor will have the answers to the even numbered problems. Time and financial constraints mean that we will not be posting solutions to these problems: sorry!

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