0.33 Phy1330: angular momentum -- torque, work and energy

Table of contents

• Preface
  • General
  • Prerequisites
  • Viewing tip
    • Figures
  • Supplemental material
• Discussion
  • Constant torque
  • Variable torque
• Example scenario
  • Part 1
  • Part 2
• Do the computations
• Resources
• Miscellaneous

Preface

General

This module is part of a book (or collection) designed to make physics concepts accessible to blind students. The collection is intended to supplement but not to replace thetextbook in an introductory course in high school or college physics.

This module explains torque, work and energy in a format that is accessible to blind students.

Prerequisites

In addition to an Internet connection and a browser, you will need the following tools (as a minimum) to work through the exercises in these modules:

• A graph board for plotting graphs and vector diagrams ( (External Link) ).
• A protractor for measuring angles ( (External Link) ).
• An audio screen reader that is compatible with your operating system, such as the NonVisual Desktop Access program (NVDA), which is freelyavailable at (External Link) .
• A refreshable Braille display capable of providing a line by line tactile output of information displayed on the computer monitor ( (External Link) ).
• A device to create Braille labels. Will be used to label graphs constructed on the graph board.

The minimum prerequisites for understanding the material in these modules include:

• A good understanding of algebra.
• An understanding of the use of a graph board for plotting graphs and vector diagrams ( (External Link) ).
• An understanding of the use of a protractor for measuring angles ( (External Link) ).
• A basic understanding of the use of sine, cosine, and tangent from trigonometry ( (External Link) ).
• An introductory understanding of JavaScript programming ( (External Link) and (External Link) ).
• An understanding of all of the material covered in the earlier modules in this collection.

Viewing tip

I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the figureswhile you are reading about them.

Figures

• Figure 1 . Work done by perpendicular component of force.
• Figure 2 . Work done by constant torque.
• Figure 3 . Power generated or consumed by a constant torque.

Supplemental material

I recommend that you also study the other lessons in my extensive collection of online programming tutorials. You will find a consolidated index at www.DickBaldwin.com .

Discussion

This section will begin by developing the equations from which you can compute the work done by a constant torque that causes a known displacement. Then it will provide a briefdiscussion of the situation where the torque is not constant.

Constant torque

One of the textbooks that I have read uses a very familiar example to illustrate that torque can do work. The example is that of a person pulling onthe rope on a power mower or outboard engine to try to get it started.

If you are unfamiliar with that scenario, many small internal combustion engines use a rope wrapped around a pulley to start the engine. When the userpulls the rope, a torque is created on the pulley by the rope. The torque causes an angular displacement of the pulley, which in turn causes certain parts insidethe engine to move. If you are lucky and everything is working properly, the engine starts.