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

Teacher Guide

 Conservation of Energy Many of the most important and powerful scientific laws are conservation laws - the amount of some physical quantity or variable is found to remain a constant; it cannot change. Energy is one of the physical quantities that is conserved in our universe. This can be stated as follows: Energy cannot be created nor destroyed. The one exception is in nuclear reactions where mass is turned into energy, and as we have seen, this occurs only in the center of stars and in nuclear reactors.
Let's look at an example of an electric light bulb. A light bulb changes electrical energy into light energy. If we were to measure these energies for one second, we might get energy numbers that look something like this:
 Electrical Energy In 100 J (joules) Light Energy Out 70 J (joules) This would suggest that energy is not conserved? Where did the other 30 J of energy go?

Remember that energy can change into more than one form simultaneously. And if you feel a light bulb it is very hot. The "missing" energy must have gone into heat energy. So, the actual energies were more like this:
 Electrical Energy In 100 J (joules) Light Energy Out 70 J (joules) + Heat Energy Out 30 J (joules)

This propensity for energy to change into more than one type of energy is extremely common. And the most common energy for this "missing" energy to go to is heat energy. Since our goal for the light bulb is for all of the electrical energy to go into light energy, the heat energy is really "lost" energy. We can rate our light bulb by measuring its efficiency, or percentage of energy that goes where we want it to go. The equation for efficiency is:

So for our light bulb above, the efficiency would be 70% as shown below:
Even though we may "lose" energy in the form of heat, the total energy is still the same. Energy is conserved. So, if all energy is conserved, we can never run out of energy! Right? As we will see, our lives and the lives of energy are not that simple.

The animation below requires the Macromedia flash player. If you don't see the animation, you can download and install the flash player from the following site: Download Flash Player

In the animation below of a spring bouncing up and down, energy is constantly changing types. The three energies involved are: spring, or elastic potential energy (EPE); gravitational potential energy (or GPE), and kinetic energy (KE). The energies are all changing in differnet ways depending on how much the spring is stretched and how high the object attached to the spring is. Note, however, that energy is conserved, the total energy stays the same (the bar on the right).

Created by Tom Chandler, OME educator, 2001-02

For more information on the law of conservation of energy and other conservation laws, check out the websites below.

 Basics of Life Law of Conservation of Energy. Conservation Laws Some diagrams of conservation laws and info on isolated systems.