ENERGY FORMS AND CHANGES
Lesson Objectives
1. Identify different forms of energy.
2. Describe how energy changes form.
Lesson Vocabulary
1. chemical energy
2. electrical energy
3. electromagnetic energy
4. mechanical energy
5. sound energy
6. thermal energy
Introduction
The man below is playing an electric guitar. He plucks the strings of the guitar with great skill. The
sounds of the music thrill the crowd. The bright stage lights add to the excitement. Unfortunately,
the lights can also make it uncomfortable for the musician. It can get really warm on stage. Do
you know why? It has something to do with the lights. This scene represents energy in many
forms. Can you name them all?
[Figure 1]How many different forms of energy can you identify in this picture?
Comparing Forms of Energy
Energy can exist in many forms. It also has the ability to do work. Think about when you do work.
You need a lot of energy. Maybe your energy comes from a good breakfast. Your body turns the
food you eat into energy. This energy gives you the strength to do work. There are many forms
of energy. They all have the ability to do work. From the picture above, can you find six forms of
energy?
The guitarist can play because he eats food. Food contains chemical energy. His body then turns
chemical energy into motion. His hands can move to play the guitar. The motion of the guitar
player's hands is a form of mechanical energy. Chemical energy is just one form of energy. That's
why it's important for you to eat right.
What about some other forms of energy in this picture? How about the stage lights? The stage
lights use electrical energy. The lights give off both light and heat. Heat is sometimes called
thermal energy. The guitar uses electrical energy. The guitar produces sound energy when the
strings are plucked.
Mechanical Energy
Mechanical energy is a combination of the energy of motion or position. This type of energy
describes objects that are moving or could move.
A moving ball can have energy from motion. An arrow can also have the energy of motion. Both
are types of mechanical energy. Can you think of some other examples?
Where does the energy of motion come from? It comes from the energy created by position. This
energy is stored energy. This means it is not moving yet, but it has the potential to move. How
can you store energy?
In the figure below, the arrow gains energy from the drawn bow. As the arrow is released, the
bow releases its stored energy and puts the arrow into motion. Can you think of some other ways
to store energy using position?
[Figure 2]
Kinetic and potential energy add up to mechanical energy.
Chemical Energy
Energy is stored in chemical compounds. This energy is called chemical energy. Chemical energy
is a form of potential energy. When bonds between atoms are broken, energy is released. The
wood in fireplaces has chemical energy. The energy is released as heat and light when the wood
burns.
Most living things get their energy from food. When food molecules are broken down, the energy
is released. It may then be used to do work, like playing ball or studying science. If you have ever
heard, "Eat a good breakfast," that's why. You need energy to do things during the day. To do
those things you need energy. You get your energy from the food you eat. That energy is stored
in your body until you need it.
How did you get to school today? If you walked, you used chemical energy from the food you
ate. What if you rode the bus or were driven in a car? Where did that energy come from? Gasoline
also has potential energy. Just like food, when the bonds between atoms in the gas are broken,
energy is released. Remember, when wood burns it gives off heat and light. When gasoline is
burned in an engine, it also gives off energy. It is this energy that makes the vehicle move.
[Figure 3]
Chemical energy is stored in wood and released when the wood
burns.
Electrical Energy
Electrons are particles in an atom. They have a negative charge. Anything that is moving has
energy, even electrons. We often refer to this motion as electricity. Electricity is the result of the
moving electrons. These electrons can move through wires. This motion is what makes it possible
to watch TV and talk on your cell phone.
Have you ever had to live without electricity? This can happen after big storms. Any type of
natural disaster can cause a loss of electricity. In what ways would a loss of electricity affect your
family?
Most of the electricity we use comes from power plants. It arrives in our homes through wires.
There are also other sources of electricity. You are probably very familiar with two of the most
common sources. You can see both of them pictured in the Figure below.
[Figure 4]
A lightning bolt is a powerful discharge of
electrical energy. A battery contains stored
chemical energy and converts it to electrical
energy.
Nuclear Energy (Advanced Topic)
The center of an atom is held together by powerful forces. This gives them a huge amount of
stored energy. This type of energy is called nuclear energy. This energy can be released and used
to do work. This happens in nuclear power plants where they split apart the nucleus of an atom.
This splitting apart is called nuclear fission.
Another type of nuclear energy happens in the Sun. Here the atoms' nuclei are not split apart.
Instead, the nuclei of the atoms are fused, or joined together. This process is called nuclear
fusion. Some of the sun’s energy travels to Earth. This energy from nuclear fusion warms the
planet and provides the energy for photosynthesis (see Figure below).
[Figure 5]
In the sun, hydrogen nuclei fuse to form helium
nuclei. This releases a huge amount of energy,
some of which reaches Earth.
Thermal Energy
Atoms are in constant motion. They have kinetic energy, the energy of motion. All that motion
gives matter thermal energy. The amount of motion that particles have is what we call
temperature.
In Figure below, you can see two items. They have different amounts of thermal energy, but the
same temperature. How can this be?
Thermal energy depends on two factors. The first is how fast the atoms are moving, or its
temperature. The second is how many atoms the object contains. Therefore, an object with more
mass has greater thermal energy. An object with less mass has less thermal energy.
Think of it this way. You have a small cup of warm water. You also have a large barrel of warm
water. Each are the same temperature. Which has the most energy? If you said the large barrel,
you would be correct. The more mass there is, the more thermal energy. If you were in a bath
tub and needed to warm the water, would you add a little warm water or a lot? Of course, you
would add the larger amount. This is because it has more thermal energy.
[Figure 6]
Atoms are moving at the same speed in the soup
on the spoon as they are in the soup in the pot.
However, there are more atoms of soup in the pot,
so it has more thermal energy.
Electromagnetic Energy
Our sun and other stars release light energy. At least this is what we see. Our Sun and stars also
emit more than just light. Scientists call the type of energy that our Sun and stars release
electromagnetic energy. This form of energy travels through space. Electromagnetic energy
includes the light we see. It also includes much more. Many of these things we know about, but
don't always think about. Electromagnetic energy includes radio waves, microwaves, and X rays.
We now have devices in our homes and offices that release these same forms of energy. We use
electromagnetic energy to make our lives better.
[Figure 7]
Radio waves, microwaves, and X rays are examples of electromagnetic energy.
Sound Energy
The drummer in Figure below is hitting the drumheads with drumsticks. This causes the
drumheads to vibrate. The vibrations pass to surrounding air particles. Vibrations then pass from
one air particle to another in a wave of energy called a sound wave. We hear sound when the
sound waves reach our ears. Sound energy can travel through air, water, and other substances.
Sound cannot travel through empty space. Sound needs particles of matter to pass it on.
You can think of sound moving through matter like falling dominoes. If they are lined up, one will
fall, hitting the next and making it fall, and so on. What if the dominoes were too far apart to
touch when they fell? This is what happens if there are no particles for sound to travel through.
Fortunately for us, space is the only place sound cannot be transmitted.
[Figure 8]
Vibrating objects such as drumheads
produce sound energy.
How Energy Changes Form
Energy often changes from one form to another. For example, the drummer transfers motion to
sound energy. When the moving drumstick strikes the drum head, the drum starts to vibrate. The
motion of the vibrating drum head creates the sound you hear. Any form of energy can change
into any other form. Frequently, one form of energy changes into two or more different forms.
Have you ever sat in front of a campfire? What are two things you notice? The fire creates light.
It is also warm by the fire, meaning it creates heat. The energy of the fire comes from the stored
energy in the wood. The wood contains chemical energy. As it burns, the chemical energy is
changed into light and heat. Not all chemical energy changes produce light and heat. Our cars
use gasoline as a fuel. Gasoline contains chemical energy. When our cars burn gasoline in their
engines, it is converted into motion and heat.
[Figure 9]
Energy is constantly changing form. Can you think of
other examples of energy conversions?
When energy changes forms, energy is conserved. What does this mean? It means that no energy
is lost. That does not mean all the energy that changes form goes where we want it. For example,
when our cars burn gasoline, all the energy does not go into motion. Some is turned into heat.
For us, this energy is wasted. Although you may start with the same amount as you end up with,
some of the energy is not useful. In the case of a car engine, some energy may turn into heat
energy due to friction. For example, not all of the energy put into a steam turbine
in Figure above changes to electrical energy. Some changes to thermal energy. This, too, happens
because of friction. In this case, it is because of the turning blades and other moving parts. The
more efficient a device is, the less thermal energy is lost. Some new appliances are very efficient.
These devices have the "Energy Star" label. You can see an Energy Star label in Figure below.
These labels tells us the appliance is efficient and reduces the use of energy.
[Figure 10]
The U.S. government’s Energy Star program certifies the energy
efficiency of appliances. Look for this label to identify those that are
energy efficient.
Lesson Summary

Forms of energy include mechanical, chemical, electrical, nuclear, thermal,
electromagnetic, and sound energy. These forms of energy can occur as either kinetic or
potential energy.

Energy often changes from one form to another. Any form of energy can change into any
other, and one form may change into two or more different forms. Energy is always
conserved when it changes form.
GUIDE QUESTIONS
Recall
1. Define mechanical energy.
2. Give an example of chemical energy.
3. What is electrical energy?
4. Name two processes that release nuclear energy (Advanced Topic).
Apply Concepts
5. If you were on the moon, no sound energy would be able to reach your ears. Explain why.
(Hint: The moon has no atmosphere.)
6. State how energy is converted by the following electrical devices: light bulb, alarm clock,
hair dryer.
Think Critically
7. Relate the thermal energy of an object to the object’s atoms.