# PHY138Y - Mechanics - Class 7 - Mon. Oct. 2, 2006

## 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)

## First Written Homework

 Each quarter will have one written homework assignment. It is to be solved as a group effort by the same teams that have been doing activities in tutorial. The first one is due Friday, October 13 by 5 PM in the "Drop Boxes" in the basement of the Burton tower of McLennan. You may access it, in pdf form, via the button to the right.

## Today's Class

I have caught up to the timetable given in the syllabus. Today we finished our discussion of Chapter 6, and began Chapter 7, getting through §7.4 - Circular Orbits.

As I said in class, Chapter 7 is where the "rubber hits the road" for some students. Thus I urge you to make sure you are on top of this material; otherwise any deficiencies will come back to haunt you when we get to Chapter 13.

### In-Class Questions

 We asked two question in class, available via the button.

#### Battleships Question

 Initially about 50% of you answered that the two ships get hit at the same time. A closer runner-up was Answer B: the furthest ships gets hit first. The four students who answered D or E are running this joke into the ground! After some discussion amongst yourselves, the most popular answer became the correct one: B. I am surprised that those of you who initially knew the right answer to this question didn't do a very good job of convincing your classmates.

#### Ball Off Mt. Everest

About 75% of the class got the right answer: B - the acceleration is approximately g. We discussed this a bit in class, including once again firing off some nerf air rockets. I hope that by the end you all understand why this is correct.

### Flash Animations

 Galileo's original argument supporting his principle of relativity. Illustrating the text's r-t-z coordinate system. A sort of crude animation of Student Workbook activity Chapter 6 #8: Tarzan swinging from a vine. The forces acting on Tarzan as he swings on his vine.

### Other Class Materials

 Pdf version of the PowerPoint on the side screens. Today's Journal.

## Suggested Problems

• Chapter 7: 19, 22, 40, 63
 The arrows let you jump to the previous/next class summaries.