# PHY138Y - Mechanics - Class 8 - Wednesday, Oct. 1, 2003

## Introduction

Newton approached the idea of a gravitational field but never quite got there.

The gravitational forces are “an endeavor of the whole directed toward a center, … a certain efficacy diffused from the center through each of the surrounding spaces.”

-- Principia

## Announcements

### Friday Representative Assembly

The Representatives from Friday's tutorials meet this week:

### Drop-In Centre

The Drop-In Centre is a place where you may ask any question about Physics.

## Today's Class

We discussed §6.3 - The Scalar Product and §6.4 - Work Done by a Varying Force.

This included a brief use of integrals from the calculus, although it will be later in the year before you are expected to know very much about these. Thus, you may treat this mathematics, which we did just like the textbook, as an introduction to a topic which your math course will be discussing in considerable detail later.

 As an example of the work done by a varying force, we discussed a spring exerting a force on a mass, described by Hooke's Law. We used a Flash animation, which you may access by clicking on the button to the right. Separate window, 17k.

Newton and Hooke hated each other. Here is a fragment of a statement by Newton about Hooke:

“This carriage towards me is very strange & undeserved, so that I cannot forbeare in stating that point of justice to tell you further … he should rather have excused himself by reason of his inability. For tis plain by his words he knew not how to go about it.”

We talked about §6.5 - Kinetic Energy and the Work - Kinetic Energy Theorem, and began §6.6 - The Nonisolated System. We shall finish §6.6 next time.

 Several alert PHY138 students pointed out after class that I made a mistake by a factor of 2 in what I wrote when were analysing the jumper problem. I have added a note in purple in the Journal file pointing out the mistake.
 You may access the "Journal" from today's class by clicking on the button to the right. Separate window, 223k.