Download What is energy?

chapter
23
Energy and Energy Resources
1
section ●
What is energy?
PS 4.1d: Different forms of energy include heat, light, electrical, mechanical, sound, nuclear, and chemical. Energy is transformed in many ways.
4.1e: Energy can be considered to be either kinetic energy, which is the energy of motion, or potential energy, which depends on relative position.
Before You Read
What does the phrase “She has a lot of energy” mean to you?
Read to Learn
The Nature of Energy
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Energy is the ability to cause change. An object that has
energy can make things happen. Look around you. Changes
are happening. Someone might be walking by. Sunshine
might be warming your desk. Maybe you can see the wind
move the leaves on a tree. What changes are happening?
What You’ll Learn
what energy is
the difference between
kinetic energy and
potential energy
■ the different forms of
energy
■
■
Highlight Forms of
Energy As you read this
section, highlight the different
forms of energy. Then write an
example of each type of energy
next to the places you
highlighted.
When is energy noticed?
You have a lot of energy. So does everything around you.
But you only notice this energy when a change takes place.
When a change happens, energy moves from one object to
another. Energy from sunlight moves to the spot on the
desktop and makes it warm. Energy from the wind moves to
leaves. All objects, including desktops and leaves, have energy.
Energy of Motion
Things that move can cause change. Suppose a bowling ball
rolls down the alley and knocks down some bowling pins.
Does this involve energy? A change happens when the pins
fall over. The bowling ball causes this change. Since energy is
the ability to cause change, the bowling ball has energy. The
energy in the movement of the bowling ball makes the pins
fall. The energy an object has because of its motion is kinetic
energy. So as a bowling ball moves, it has kinetic energy. If
an object is not moving, it does not have kinetic energy.
A Organize Information
●
Make the following Foldable to
organize information about the
nature of energy, the energy of
position, and the different forms
of energy.
Reading Essentials
21
How are kinetic energy and speed related?
What would happen to the bowling pins if the bowling
ball rolls faster? More of the pins might fall down or they
might move farther. A faster bowling ball causes more
change to happen than a slower bowling ball. The faster the
bowling ball goes, the more kinetic energy it has. This is
true for all moving objects. Kinetic energy increases as an
object moves faster.
Apply Does a slowermoving object have more
or less kinetic energy than a
faster-moving object?
B Compare and Contrast
●
Make the following Foldable to
compare and contrast kinetic
energy and potential energy.
Picture This
2.
Determine Which vase
on the shelves has the most
potential energy?
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Energy and Energy Resources
How are kinetic energy and mass related?
Suppose you roll a volleyball down the alley at the same
speed as a bowling ball. Will the volleyball move the pins as
far as the bowling ball will? The answer is no. The volleyball
might not knock down any pins.
How are the volleyball and the bowling ball different?
They are moving at the same speed, but the volleyball has
less mass. The volleyball has less kinetic energy than the
bowling ball because it has less mass. Kinetic energy
increases as the mass of an object increases.
Energy of Position
An object can have energy even if
it is not moving. Look at the vase on
top of the bookcase. The vase does not
have any kinetic energy because it is
not moving. What if it accidentally
falls to the floor? Changes happen.
Gravity pulls the vase downward. The
vase has kinetic energy as it falls.
Where did this energy come from?
When the vase was sitting on the
shelf, it had potential (puh TEN chul)
energy. Potential energy is the energy
stored in an object because of its
position. The position of the vase is
its height above the floor. As the vase
falls, the potential energy is
transformed, or changed, from one form to another. It is
transformed into kinetic energy. A vase has more potential
energy if it is higher above the floor. Potential energy also
depends on mass. The more mass an object has, the more
potential energy it has. The objects in the figure have
different amounts of potential energy.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
1.
Forms of Energy
Food, sunlight, and wind have energy. But they have
different kinds of energy. The energy in food and sunlight is
different from the kinetic energy in the wind. The warmth
you feel from sunlight is different from kinetic energy or
potential energy.
What is thermal energy?
When you sit near a sunny window, you get warm. The
feeling of warmth is a sign that you are getting more
thermal energy. Thermal energy is energy of an object that
increases as the object’s temperature increases. All objects
have thermal energy. In the figure below, a cup of hot
chocolate has more thermal energy than a bottle of cold
water. The bottle of cold water has more thermal energy
than a block of ice with the same mass.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Picture This
3.
Identify Circle the object
with the greatest thermal
energy. Put a box around
the object with the least
thermal energy.
4.
Explain What has stored
chemical energy that your
body uses?
Your body makes thermal energy all the time. Chemical
reactions that happen inside your cells make thermal energy.
Where does this energy come from? Thermal energy is
released by chemical reactions. Thermal energy comes from
another kind of energy called chemical energy.
What is chemical energy?
Chemical energy is the energy stored in chemical bonds.
Some of this energy is released when chemicals are broken
apart and new chemicals are made.
For example, food has chemical energy that your body
uses to help you think, move, and grow. Food has chemicals,
such as sugar. The chemicals are made of atoms that are
bonded together. Energy is stored in the bonds between
atoms. These chemical bonds can be broken down in your
body to release energy.
Also, the flame of a candle comes from chemical energy
stored in wax. When the wax burns, chemical energy changes
into thermal energy and light energy.
Reading Essentials
23
What is radiant energy?
5.
Summarize When does
light energy change to
thermal energy?
Light from the candle flame travels very fast through the
air. It moves at a speed of 300,000 km/s. This is fast enough
to circle Earth almost eight times in 1 s. When light hits an
object, three things can happen. The light can be absorbed
by the object, reflected by the object, or be passed through
the object. When an object absorbs light energy, the object
can get warmer. The light energy changes into thermal
energy. You can feel this happening if you wear a black shirt
outside on a sunny day.
The energy carried by light is radiant energy. You can
use electrical energy to make radiant energy. Imagine a
metal heating coil on an electric stovetop. As it is heated,
it becomes red hot. The hotter it gets, the more radiant
energy it gives off. Electrical energy is being used to make
the heating coil warmer.
6.
Compare Which of the
following can carry the
most current?
a.
b.
c.
d.
9-V battery
220-V electrical outlet
12-V battery
110-V electrical outlet
Electrical energy is used in many ways. Electrical energy
is carried by the electric current that comes out of batteries
and electrical outlets. Electrical lighting uses electrical energy.
Look around at all the devices that use electrical energy.
The amount of electrical energy depends on the voltage.
The current out of a 120-V electrical outlet can carry more
energy than the current out of a 1.5-V battery. Large power
plants are needed to make the huge amount of electrical
energy people use every day. About 20 percent of the
electrical energy made in the United States comes from
nuclear power plants.
What is nuclear energy?
Nuclear power plants use the energy stored in the nucleus
of an atom to make electricity. Nuclear energy is the energy
in the nucleus of every atom. Nuclear energy can be
transformed into other kinds of energy. Releasing nuclear
energy is difficult. Complicated power plants are necessary
to produce nuclear energy. Releasing nuclear energy from an
atom is very different from releasing chemical energy from
wood. To do that, all you need is a lighted match.
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Energy and Energy Resources
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
What is electrical energy?
After You Read
Mini Glossary
chemical energy: the energy stored in chemical bonds
electrical energy: the energy carried by the electric current
that comes out of batteries and electrical outlets
energy: the ability to cause change
kinetic energy: the energy an object has because of
its motion
nuclear energy: the energy in the nucleus of every atom.
potential energy: the energy stored in an object because of
its position
radiant energy: the energy carried by light
thermal energy: the energy of an object that increases as
temperature increases
1. Read the key terms and definitions in the Mini Glossary above. On the lines below,
explain the difference between the terms potential energy and kinetic energy.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
2. Match the forms of energy with the correct examples. Write the letter of each example in
Column 2 on the line in front of the form of energy it matches in Column 1.
Column 1
Column 2
1. potential energy
a. the energy that makes a television work
2. kinetic energy
b. a lamp giving off light
3. electrical energy
c. the energy in food
4. thermal energy
d. a ball rolling
5. chemical energy
e. a book sitting on a shelf
6. nuclear energy
f. the energy in a cup of hot tea
7. radiant energy
g. the energy in an atom’s nucleus
3. You were asked to highlight the different forms of energy in this section. What do you
think would be another way to help you remember the different forms of energy?
Visit glencoe.com to access your textbook, interactive games,
and projects to help you learn more about energy.
End of
Section
Reading Essentials
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chapter
23
Energy and Energy Resources
2
section ●
Energy Transformations
PS 4.1c: Most activities in everyday life involve one form of energy being transformed into another. Energy, in the form of heat, is almost always one of the products of
energy transformations. 4.3a: In chemical reactions, energy is transferred into or out of a system. Light, electricity, or mechanical motion may be involved in such
transfers in addition to heat. 4.4d: Electrical energy can be produced from a variety of energy sources and can be transformed into almost any other form of
energy. Also covered: 4.1d, 4.1e, 4.5a, 4.5b.
What You’ll Learn
to apply the law of
conservation of energy
■ energy changes form
■ how electric power
plants make energy
■
Before You Read
Explain how you used one kind of energy today.
Read to Learn
Highlight the main point in each
paragraph as you read this
section. Study the main points,
then state each point in your
own words.
Changing Forms of Energy
Energy can have different forms such as chemical,
thermal, radiant, and electrical. All around you, at all times,
energy is being transformed. This means it is changing from
one form to another. You see some of these transformations
when you notice a change in your environment. Forest fires
are an example of a change involving energy. They can
happen naturally because of lightning strikes. Changes also
happen as a mountain biker pedals up a hill.
How can you track energy transformations?
C Describe Make the
●
following Foldable. Inside,
describe the law of conservation
of energy and give examples.
Law of
Conservation
of Energy
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Energy and Energy Resources
A mountain biker’s leg muscles transform chemical energy
into kinetic energy as he pedals. The kinetic energy of his
leg muscles is transformed into kinetic energy of the bicycle
as he pedals. As he moves up the hill, some of this energy is
transformed into potential energy.
Some energy also is transformed into thermal energy. His
body is warmer because chemical energy is being released.
The parts of the bicycle are warmer too because of friction.
When energy is transformed, heat energy usually is made.
People exercising, cars running, and living things growing
all produce heat.
The Law of Conservation of Energy
The law of conservation of energy states that energy is
never created or destroyed. The only thing that changes is
the form of the energy.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Identify Main Ideas
When the biker is resting at the top of the hill, all of his
original energy is still around. Some of his energy changed
into potential energy. Some changed into thermal energy.
No energy is missing. It can all be accounted for.
Changing Kinetic and Potential Energy
The law of conservation of energy can be used to identify
energy changes in a system. For example, tossing a ball into
the air and catching it is a simple system. As the ball leaves
your hand, most of its energy is kinetic. As it rises, it gets
slower. It loses kinetic energy. The kinetic energy is changed
into potential energy. The amount of kinetic energy that it
loses equals the amount of potential energy that it gains.
The total amount of energy stays the same.
1.
Draw Conclusions
At what point does the ball
have the most potential
energy?
a. when it reaches its
highest point
b. when it leaves your hand
c. just before you catch
the ball
d. halfway up in the air
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Energy Changes Form
Energy changes form all the time all around you. Many
machines transform energy from one kind to another. For
example, an automobile engine transforms the chemical
energy in gasoline into kinetic energy. Some of the chemical
energy also is transformed into thermal energy, making the
engine hot. An engine that converts chemical energy into
more kinetic energy and less thermal energy is a more
efficient engine. New kinds of cars use an electric motor
along with a gasoline engine. These engines are more
efficient so the car can travel farther on a gallon of gas.
How is chemical energy transformed?
Chemical energy can be transformed into kinetic energy
inside your body. This happens in muscle cells. Chemical
reactions take place and cause certain molecules to change
shape. Many of these changes make your muscles contract.
This makes a part of your body move.
Biomass Biomass is the matter in living organisms.
Biomass contains chemical energy. When organisms die,
chemical compounds in their biomass break down. Bacteria,
fungi, and other organisms help change these chemical
compounds into simpler chemicals. These simpler chemicals
are used by other living things.
Thermal energy also is released when these biomass
breaks down. For example, as a compost pile decomposes,
chemical energy is changed into thermal energy. The
temperature of a compost pile can reach 60°C.
2.
Summarize What kind
of energy does bacteria and
fungi help transform?
Reading Essentials
27
How is electrical energy transformed?
You use electrical energy every day. When you flip a light
switch or turn on a radio, electrical energy is transformed
into other forms of energy. You use electrical energy when
you plug something into an electrical outlet or use a battery.
Hearing Sounds The figure shows how electrical energy is
transformed into other kinds of energy when you listen to a
radio. A loudspeaker in the radio changes electrical energy
into sound waves. The sound waves travel to your ear. This is
energy in motion. The energy carried by the sound waves
makes parts of your ear move too. This energy of motion is
transformed into chemical and electrical energy in nerve
cells. The nerve cells send the energy to your brain. Your
brain figures out that the energy is a voice or music. Where
does the energy go after the brain? It finally is transformed
into thermal energy.
Picture This
3.
Identify What kind of
What changes into thermal energy?
4.
Check Understanding
How can thermal energy be
used to make kinetic energy?
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Energy and Energy Resources
Different kinds of energy can be transformed into thermal
energy. When something burns, chemical energy changes into
thermal energy. Electrical energy changes into thermal energy
when a wire that is carrying an electrical current gets hot.
Thermal energy can be used to heat buildings and keep
you warm. Thermal energy also can be used to heat water.
If you heat water to its boiling point, it changes to steam.
Steam can be used by steam engines to make kinetic energy.
Steam engines were once used on steam locomotives to pull
trains. Thermal energy also can be transformed into radiant
energy. This happens when you heat a metal bar until it is
so hot that it glows and gives off heat.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
energy travels through the
air from a radio?