0.23 Phy1210: energy -- internal and external forces

Table of contents

• Preface
  • General
  • Prerequisites
  • Supplemental material
• Discussion
• 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 internal and external forces 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.

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

Work

You learned in an earlier module that work is done on an object when that object is displaced by a force. You further learned that the amount of work doneis proportional to the product of the force, the displacement distance, and the cosine of the angle between them.

Mechanical energy

You also learned in an earlier module that mechanical energy is the energy that is possessed by an object due to its motion or due to its position (where position includes the deformation, stretching, compressing, etc., involved in elastic potential energy) .

Mechanical energy can be eitherkinetic energy resulting from motion orpotential energy resulting from the position of the object.

Two categories of force

When speaking of work and energy, we can categorize force into two categories:

• internal or conservative force
• external or non-conservative force

In theory, the distinction between the two categories is not complicated. Work done on an object solely by internal forces cannot change the totalmechanical energy possessed by an object. Work done on an object by external forces can change the total mechanical energy possessed by an object.