National Teacher Enhancement Project

## Middle School Home Energy Audit

### ENERGY

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WHAT IS ENERGY?

• Do you use energy?
• What items require more energy that others?
• How would your life be different without energy to make things go?

Energy lets us do work

Energy is the ability to do work. As such, energy is important to all living things in order to maintain life functions from the smallest part of a cell to the organism as a whole. Humans, on the other hand, use energy to modify their environment and perform work. Energy is measured by the amount of work it is able to do. The units for measuring energy are joules (J).

Work involves a change in a system. This might be changing something's position like moving things as you pick up a room. Other types of changes that requires work would be heating or cooling a building, generating a image on the television screen, and moving a speaker cone back and forth the make sound (like on headphones or a stereo). Since different tasks require different amounts of work, some things require more energy than others.

The work that energy allows us to do can typically be divided into five main tasks:

1. Energy produces light.

2. Energy produces heat.

3. Energy produces motion.

4. Energy produces growth.

5. Energy powers technology.

Work is expressed as a force applied over a distance. The units used to describe work are joules, which equal the amount of energy needed to accomplish a particular task. The equation for work (W) is force (F) multiplied by distance (d):

Energy exists in different forms

Have you ever been at the top of a steep hill on a bicycle? It was probably fun to coast down the hill expending (using) little effort as the bike moved. In that case, you experienced both forms of energy: potential energy and kinetic energy.

Kinetic energy is the energy of moving objects. As you sped down the steep hill on your bicycle, you were moving and therefore had kinetic energy. But where did this energy come from? You probably already know that it came from your position at the top of the hill. At the top of the hill, you had the ability to do work (move the bicycle) purely because of where you were. This resting or waiting energy is potential energy. You had the potential or possible ability to perform the work of moving the bicycle.

Whenever you work with energy, you probably are dealing with both forms together in the same system. The ratios of potential energy to kinetic energy may be different in different types of energy. The combination of kinetic and potential energies result in the different types of energy we see and use in daily life. Some different types of energy are:

• Mechanical energy (moving objects and their positions)
• Radiant energy (light and solar energy)
• Sound energy (compression waves of air or another medium)
• Chemical energy (including the food you eat and fuels we burn)
• Thermal or heat energy (molecules moving faster means more heat)
• Electrical energy (electrons moving through a wire)
• Nuclear energy (energy locked in the nucleus of an atom)

Energy can be transferred, but not destroyed

In the example of riding a bicycle down a steep hill, you begin with a lot of potential energy at the top of the hill and gain kinetic energy as you coast down the hill. According to the First Law of Thermodynamics, energy cannot be created or destroyed. If you are not making the kinetic energy (movement down the hill), where does it come from? The answer is simple: your potential energy at the top is transformed into kinetic energy as you speed along.

Energy can be transferred from one form to another. Energy forms can be changed to make the energy useful to us. For example, fossil fuels like coal and oil can be burned to heat water (kinetic energy since the molecules of water move faster as they heat) that turns a turbine to generate electricity that you use to operate a stereo. Each step involves a transformation of energy from one type to another. But remember, the energy is not being created or destroyed, just transferred. This means that if you begin with 1000 joules of energy and transfer it several times, the total amount of energy at the end must equal 1000 joules.

Electrical Energy

Electricity is one of the most common energy sources we use. Electricity is the movement of electrons. So what are electrons? They are tiny charged particles found in atoms. Electrons must flow in closed loops called circuits. The path must be complete before electrons can move. These circuits are found everywhere you find electrical energy in use. If you break the loop, the circuit is incomplete and the electrons stop flowing. This is why when you flip a switch, electrical devices turn on and off. Simply put, closing a circuit turns the device on, and opening the circuit stops the flow of electrons turning the device off.

As these electrons flow through circuits, they are capable of doing work. Turning a fan blade on an electric fan, heating a wire filament inside a lightbulb so it glows to produce light, and directing an electron beam to create an image on the screen of a television are all types of work that can be done with electricity.

Electrical energy originates from the conversion of several different energy sources. These original sources can be chemical as in a battery, mechanical as in moving water that turns a generator, radiant as with solar electric cells, and thermal as with steam turning generators in electrical power plants. These are only a few of the energy conversions you will learn about later.

Electricity is converted to other energy forms as it does work. Here are a few ways it is converted for our use:

• Electricity passing through the coils on an electric stove is converted to thermal energy allowing us to cook on the hot surfaces.
• Electricity is converted to kinetic energy as it passes through an electric motor.
• Electricty is converted to radiant energy as it passes through a lightbulb filament.

Students: Click on the button at the left to connect to the Energy Worksheet.

Created for the NTEP II Fermilab LInC program sponsored by Fermi National Accelerator Laboratory Education Office and Friends of Fermilab, and funded by United States Department of Energy, Illinois State Board of Education, North Central Regional Technology in Education Consortium which is operated by North Central Regional Educational Laboratory (NCREL), and the National Science Foundation.

Authors: Sue Emmons, Powell Middle School, Littleton, CO; Kevin Lindauer, John F. Kennedy High School, Denver, CO; Linda Lung, National Renewable Energy Laboratory, Golden, CO; John Sepich, Scott Carpenter Middle School, Westminster, CO; ; Janet Stellema, Monarch K-8, Louisville, CO.
Created: September 9, 1998 - Updated: June 29, 2001.
URL: http://www-ed.fnal.gov/ntep/f98/projects/