PHY138Y - Mechanics - Class 2 - Wednesday Sept. 10, 2003

Administration and Organisation

First, today is the last day to change your tutorial or laboratory section with ROSI. After today see Dr. Savaria in MP901A to change your tutorial section; see Dr. Serbanescu in MP124 to change your laboratory section.

Second, we will be establishing PHY138 Representative Assemblies as a mechanism for students and staff to discuss matters of organisation and structure of the course. Further information appears in the PHY138 home page at:

At your first tutorial, next week, you will choose one Representative for the Assembly. The person that you choose must not only be willing to act on your behalf, but must be available on Fridays at 12 noon for one hour.

The first Assembly will be with Representatives from Wednesday's tutorial only. It will meet on Friday, September 19 at noon in MP713.

Learning Physics

We reviewed the material on learning Physics from the first class, and discussed one of the most important skills in order to do well in your studies: Problem Solving.

We have put together a seven-step list to guide you in solving problems:

  1. Carefully read the problem to be sure you understand it.
  2. Draw a diagram with appropriate labels and coordinate axes if needed.
  3. Guess the answer to the problem. Use any principle, concept, symmetry that may be appropriate to make the guess.
  4. Cast the problem into an equation or set of equations.
  5. Solve the equation or equations to get an algebraic form of the answer.
  6. If the problem is numeric, after all the mathematics has been done substitute the numbers and their units into the equations. Determine the units of the answer.
  7. Compare your answer to your initial guess. Are they the same? If not, why? Is the answer reasonable? Is the answer correct? Are the units correct?

A more complete discussion of learning Physics and solving problems appears in the PHY138 home page at:

In class, we emphasised Step 3 in the above list, guessing the answer, by showing a quotation by one of the greatest Physicists and teachers: John A. Wheeler.

"WHEELER'S FIRST MORAL PRINCIPLE. Never make a calculation until you know the answer. Make an estimate before every calculation, try a simple physical argument (symmetry! invariance! conservation!) before every derivation, guess the answer to every puzzle. Courage: no one else needs to know what the guess is. Therefore make it quickly, by instinct. A right guess reinforces this instinct. A wrong guess brings the refreshment of surprise."

-- Taylor and Wheeler, Spacetime Physics, pg. 60. Our text gives a fragment of this on pg. 12.

Note: in class we showed this quotation in the context of our discussion of §1.5 - Order-of-Magnitude Calculations.

Textbook Reference

Here is a list of the chapters I think we will be covering in this quarter of the course. The list is subject to change, and any such changes will be announced.

Chapter Comment
1 - Introduction and Vectors
We will defer §1.6 until after you have studied error analysis in the lab. We will discuss §1.11 when we begin doing some real problems.
2 - Motion in 1 Dimension
Skip §2.8
3 - Motion in 2 Dimensions
Skip §3.6
4 - Laws of Motion
Skip §4.8
5 - More Applications of Newton’s Laws
Only discuss §5.2, §5.6 and §5.7
6 – Energy and Energy Transfer
Skip §6.7 and §6.9
7 – Potential Energy
Skip §7.8
8 - Momentum and Collisions
Skip §8.7
10 - Rotational Motion
Only discuss §10.1, §10.2, §10.3, §10.5 §10.8 and §10.9

Unless explicitly stated otherwise, material not discussed in class will not be the subject of questions on the tests or the exam.

The above table correctly indicates that we will not be discussing Chapter 9 - Relativity.

Chapter 1

Recall that we discussed in the first class the fact that the concepts of Physics are hierarchal: each concept builds on previous ones. Chapter 1 is largely concerned with the most basic concepts that we will be using throughout the year. Chapter 2 will build on these concepts, Chapter 3 will build on the concepts of Chapter 2, and so on throughout the academic year.

We discussed the material of Chapter 1 in today's class. We almost finished §1.9. We deferred discussion of §1.6 - Significant Figures until you have learned some error analysis in the laboratory. Next class we will finish Chapter 1 and begin Chapter 2.

As part of our introduction to vectors, we showed a Flash animation illustrating the meaning of the words distance and displacement. You may access the animation by clicking the button to the right. It will appear in a separate window, and has a size of 6.3k.
We used some Flash animations in our discussion of vectors. You may access these by clicking on the appropriate link to the right. Each will appear in a separate window.
You may also access the "Journal" file that I wrote during the lecture by clicking on the button to the right. It will appear in a separate window, and has a size of 132k.
The arrows jump to the previous/next class summary.