Unit 5 - Work and Energy CHAPTER 8 CONCEPTUAL PHYSICS BOOK CHAPTER 6 PHYSICS BOOK

Part 1 WORK, ENERGY, AND POWER

A New Perspective on Motion  We have been analyzing motion through the perspective of Newton’s Laws dealing with acceleration, velocity, and displacement.  In this chapter, we will look at motion from a different perspective – that of work and energy.

What is Work?  When a force acts upon an object and causes its displacement, it is said that work has been done on the object.  The force MUST cause a displacement! No work is done if the object doesn’t move.

Is There Work? 1. A woman pushes a shopping cart across the floor.  YES – Force causing displacement. 2. A man pushes against a wall.  NO – No displacement 3. A book falls off a table to the ground.  YES – Gravity provides the force to cause displacement 4. A child holds a book over her head while she stands on a moving walkway.  NO – The force is not causing the displacement.

Calculating Work

Units for Work

Example #1

Example #2

Example #3

Example #4

Energy  Energy (E) – the ability to do work.  Types of energy:  Mechanical – kinetic energy + potential energy  Electrical  Nuclear  Heat  Chemical  Sound

Kinetic Energy

Kinetic Energy Example

Work-Energy Theorem

Work-Energy Theorem Example 1

Work-Energy Theorem Example 2

Gravitational Potential Energy

Potential Energy Example