PHY138Y - Mechanics - Class 7- Monday Sept. 29, 2003

Introduction

"Newton was not the first of the age of reason. He was the last of the magicians, the last of the Babylonians and Sumerians, the last great mind which looked out on the visible and intellectual world with the same eyes as those who began to build our intellectual inheritance rather less than 10,000 years ago.”

John Maynard Keynes (1963)

Getting Into and Out Of Convocation Hall

We are proposing a convention with BIO150 (which meets just before us) and SOC101 (which meets just after us on Wednesdays):

• On the main floor there are four doors.
• Define the "North Doors" as the pair that face towards University College.
• Define the "South Doors" as the pair that face towards the CN tower.
• Enter Con Hall via the North Doors and leave via the South Doors.

How Many Problems Should You Solve?

As we say repeatedly, the heart of learning Physics is in solving problems. Thus, the more problems you solve the better. You might consider:

• Solving at least a couple of problems for each section of the textbook.
• Choosing black (straightforward), blue (intermediate) and red (challenging) problems.
• Choosing problems for which the answer or the full solution is available.

For problems with full solutions, don't peek! Looking at the solutions to problems you have not attempted to solve is unlikely to teach you anything.

When you get a problem wrong, then unless you made a trivial mathematics mistake it is likely that there are one or more concepts which you don't yet fully understand. Thus, doing problems is a diagnostic test of your understanding.

Problem Set #4

You may access the problem set by clicking on the button to the right. It is due by 5PM Monday October 6 in the "Drop Boxes" in the basement of McLennan. The file is in pdf format, with a size of 10k.

Today's Class

We finished Chapter 4. The discussion followed the text fairly closely, except that we extended the analysis of the text's Example 4.5 to similar situations; this extension is extended again in this week's Problem Set.

We discussed §5.2 - Newton's Second Law Applied to a Particle in Uniform Circular Motion, §5.6 - The Fundamental Forces of Nature, and §5.7 - The Gravitational Field.

We then began Chapter 6 - Energy and Energy Transfer. We demonstrated some concepts using "air pucks" which are similar to air hockey games and also to the Air Table experiment in the lab. The Guide Sheet for this non-core second-term experiment, in pdf format, is:
http://faraday.physics.utoronto.ca/IYearLab/airtable.pdf.

As part of the demonstration, we talked about how Leibniz and others realised that at least for some types of collisions the quantity:

is the same number before and after the collision, i.e. it is conserved. Since this was before technical definitions of words like force existed, they named mv² the vis viva, which is usually translated as "life force."

We discussed §6.1 - Systems and Environments, although I introduced much of this material when we did the Extended Example 4.5 earlier today. We then introduced the work as in §6.2 of the text.

I mentioned that the units of work, joules J = kg m² / s², were identical to the units of vis viva. This should not be interpreted to mean that they are the same, only that they have the same units.

You may access the "Journal" from today's class by clicking on the button to the right. Separate window, 223k.

The arrows jump to the previous/next class summary.