Introduction

The Energy Story

  Energy Is Born
  Energy Types
  Energy Changes
  Energy Generation

The Energy Problem

  Conservation of Energy
  Aging of Energy
  Finite Resources
  The Oil "Crisis"
  Energy Pollution
  Discussion Topics

The Energy Solution

  Conserving Electricity
  Appliance Efficiency
  Heating Conservation
  Renewable Energy

Web Links

Teacher Guide

About the Author


Secret Lives Title - The Energy Story


Energy Changes

Not only can energy change from one type into another, energy can even change into several other types at the same time. Sometimes it may seem that energy is being changed from one form into another, but the first energy is only causing another source of energy to be turned on. This can cause some confusion when energy changes types over and over again in what we might call energy "chains."


Energy Chains
Below there are several examples. The first few illustrate how energy might change into two types of energy. The second illustrates an energy chain or a continuous changing of energy. And the third illustrates an energy chain that is broken, the energy does not continue to change but causes another energy to be turned on. Make sure you understand these examples before continuing.
 
Energy Changing into Several Types
 
Example Description
Energy In
Energies Out
cruise missile graphic
Cruise Missile Gaining Altitude
Chemical

Gravitational
+
Kinetic

lightning graphic
Lightning
Electrical
Heat
+
Light
+
Sound
Energy Chains
alarm clock graphic
Wind Up Alarm Clock Ringing
Spring
Mechanical
Kinetic
(Sound)
Note: Sometimes it is hard to tell whether the energy is changing into two forms simultaneously or sequentially. In this case the spring is making the parts of the bell move which then hit to make the sound.
hammer hitting nail graphic
A Hammer Hitting a Nail
Kinetic
Kinetic
Heat
Note: In this example the moving hammer drives the nail into the wood giving it initially kinetic energy. But after the nail is driven into the wood, the nail stops. Where did the kinetic energy go? The kinetic energy goes into heat. Many energy changes are accompanied by part of the original energy turning into heat, and when the energy seems to disappear, it often has gone into heat energy. This "loss" of energy into heat will be important later when we see how the "lives" of energy are used up.
Broken Energy Chain
guilitine graphic
A Person Pulls a Cord of a Guillotine
(to chop a cabbage)
Chemical
arrow to right graphic
Mechanical
arrow to right graphic
Mechanical
NOT arrow to right graphic
Gravitational
arrow to right graphic
Kinetic
Note: The person's chemical energy (from food) allowed the movement of a hand, or mechanical energy, to move the cord, mechanical energy. This is the end of the chain. The cord pull allowed the energy already stored in the guillotine blade, or gravitational energy, to turn into kinetic energy. The gravitational energy was already stored and did not come from the mechanical energy of the moving cord.