PHY138Y - Mechanics - Class 3 - Mon. Sept. 20, 2004


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

-- Newton


Representative Assemblies

PHY138 will have Representative Assemblies. These are a small group of students and me. We will talk about issues of communication and organisation in the course. We will not talk about the content of the course.

There will be three assemblies: one is for the Wednesday tutorials, one for the Thursday tutorials and the third for the Friday tutorials. Each tutorial group will choose a Representative using any method that you wish.

Each Assembly will meet every three weeks. They will be:

The first meeting will be the Assembly for Wednesday tutorials, and will meet this Friday, Sept 24 in MP713.


The STudent Online Record Management (STORM) facility provides you with a mechanism to check your:

You will need to use a login and password to access the software. These are:

Your student number.
Your surname, exactly as it appears your student card. The password is case-sensitive, so distinctions between upper and lower case letters count. Include all spaces, apostrophes, etc. exactly as on your student card.

The software is now ready for you to access it. The URL is:

The URL is case-sensitive and the trailing slash is required.

The lab will have its own STORM database, but not yet.

All Those @$*&^! Web Pages

Here is a diagram of the main web pages for the theoretical part of the Mechanics section of PHY138, i.e. the lecture and tutorial components of the course this quarter.

The links are also shown in red.

  • The PHY138 Home Page and the PHY138 Mechanics page link to everything, including each other.
  • MasteringPhysics, WebCT and STORM do not link to anything else.
  • The PHY138 Mechanics page links to the class summaries.
  • The PHY138 Mechanics page contains the detailed curriculum.


Tutorials begin this week.

The final locations of the tutorial groups are still not quite finalised. Dr. Savaria promises that this will be done by tomorrow.

You can find out your tutorial group and where it meets from:

In your first tutorial, part of the time will be spent using the McDermott, Shaffer et al. workbook Tutorials in Introductory Physics. This is not the Homework booklet, which looks almost identical but says "Homework" on the lower left corner of the cover. You will do the following exercise:

Part I of the Acceleration in One Dimension activity. This is on pages Mech-11 - Mech-13 of the booklet. You will not do the other parts of the activity.


About Tests and the Final Exam

The following things are likely to appear as questions on the tests and final exam:

Homework Assignment #2

This assignment is due in the "Drop Boxes" for your tutorial by 5 PM on Monday, September 27. You may access the assignment, in pdf format, by clicking the button to the right. It will appear in a separate window.

Problem Solving

Although the tests and Final Exam in PHY138 will have many conceptual question, there will be some conventional numerical problems. In class we discussed techniques for effective solving such problems. We ended up with a list:

  1. Carefully read the problem to be sure you understand it.
  2. Draw a diagram with appropriate labels and coordinate axes if needed. A clever choice of a coordinate system now can save you a lot of work later.
  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 lovely but more lengthy discussion of problem solving may be found by clicking the button to the right. It is in html format and will appear in a separate window.

About This Week's Classes

Chapter 1, which we began last class and finished today, deals with some aspects of Physics' description of the universe: units, coordinate systems, and vectors. Chapters 2 and 3, which we will be discussing for the next couple of classes, develops the description of motion in terms of speed, velocity, and acceleration; of course this description is largely in the language of mathematics.

All of this material will be needed for our study of Physics, but is largely just preparation for that study. We start doing "real" Physics with Chapter 4, which we should get to next Monday.

Flash Animations

We showed some Flash animations in class. In order to view them you need the Flash player installed on your computer; it is available free from The current version of the Player is 7; if your version is less than 6 you should upgrade. You may access the animations with the links below. Each will appear in a separate window.

Illustrating the difference between distance and displacement.
Addition of 2 vectors
Addition of 3 vectors
Subtracting 2 vectors
Unit vectors
Adding vectors using cartesian components

Vector Notation

The textbook uses bold-face for vectors: A.

Since it is very hard to use bold-face when writing by hand, in class we indicate vectors by putting an arrow over the symbol, as shown to the right.

The textbook indicates the magnitude of a vector either by putting vertical lines around it, |A|, or just writing it in a non-bold face: A.

In class we will use the same sort of notation. Either vertical lines, , or just the letter:

The textbook indicates unit vectors pointing in the x, y, and z directions respectively as i, j, and k.

In class, we indicate that the vectors are of length one by putting a little "hat" (a caret sign) over them.

MasteringPhysics software uses another notation for unit vectors. It uses caret signs, as I do in class, but puts them over the letters x, y, and z instead of i, j, and k.

In-Class Question

We did an In-Class Question. You may access a pdf version of the question by clicking on the button to the right; it will appear in a separate window. The class did very well on this question: almost 80% or so got it correct.

Reminder: you need at least Version 5 of the Acrobat reader to view the In-Class Questions, and I have disabled printing.

The correct answer is 2) slows down all the time.

Today's Journal

The button to the right accesses today's Journal. Separate window.