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HIGH SCHOOL SCIENCE
Physical
Science 5:
Energy
WILLMAR PUBLIC SCHOOL
2013-2014 EDITION
C HAPTER 5
Energy
In this chapter you will:
1. Describe the relationship between work and energy
2. Relate kinetic energy to mass and speed
3. Analyze how potential energy is related to an
object’s position
4. Define gravitational potential energy and elastic
potential energy
5. Describe the major forms of energy
6. Describe the law of conservation of energy
7. Classify renewable and nonrenewable energy
resources
S ECTION 5.1
Imagine you have been swimming for a long time. You are
tired. Some friends ask you to play volleyball, but you say that
you do not have the energy. What exactly do you mean?
What is energy?
Energy
Energy is the ability to do work. In other words, energy is
transferred by a force moving an object through a distance.
When you hit a volleyball, you move it. When you jump and
run, you move yourself. Playing volleyball, jumping and
running all take energy. Sound and motion are examples of
energy in action.
O BJECTIVES :
1. Describe the relationship between work and
energy.
2. Relate kinetic energy to mass and speed.
3. Analyze how potential energy is related to an
object’s position.
4. Define gravitational potential energy and
elastic potential energy.
Vocabulary:
energy
work
joule
kinetic energy
potential energy
elastic potential energy
gravitational potential energy
Work and energy are closely related. Work is a transfer of
energy. When work is done on an object, energy is transferred
to that object.
Both work and energy are typically measured in joules (J).
Recall that 1 joule equals 1 newton-meter, the work done
when an object is moved 1 meter by a 1-newton force.
Although energy can take many different forms, it can always
be measured in joules.
All energy can be considered to be kinetic energy, potential
energy, or the energy in fields such as those produced by
electromagnetic waves. Many forms of energy can be
classified into two general types: kinetic energy and potential
energy.
The energy of motion is called kinetic energy. The kinetic
energy of any moving object depends upon its mass and
speed. To calculate the kinetic energy of an object in joules,
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multiply ½ by the object's mass (m) in kilograms and the
square of its speed (v) in meters per second.
Kinetic Energy = 1/2 mv2
Potential energy is energy that is stored as a result of
position or shape. Plucking a string and lifting a book are two
examples of stored energy—energy with the potential to do
work. Two forms of potential energy are gravitational
potential energy and elastic potential energy. Potential energy
that depends upon an object's height is called gravitational
potential energy. This type of potential energy increases
when an object is raised to a higher level. An object's
gravitational potential energy depends on its mass (m), its
height (h), and the acceleration due to gravity (g). The
potential energy of an object that is stretched or compressed
is known as elastic potential energy.
Potential Energy = mgh
Section Review:
1. How are energy and work related?
2.What unit used to measure work and/or energy?
3. What can all energies be considered?
4.What does kinetic energy depend on?
5. What is the equation for kinetic energy?
6.What are some examples of potential energy?
7. What are the two forms of potential energy?
8.What does gravitational potential energy depend on?
9.How is mechanical energy related to potential energy and
kinetic energy?
10.Can an abject have both kinetic energy and potential
energy at the same time? Explain.
Objects can have both potential energy and kinetic energy.
The total amount of potential energy and kinetic energy that
an object has is called mechanical energy.
Energy is not matter, because it does not have mass or take up
space. You cannot see energy, but you can see what energy
does. Each kind of energy can change into other kinds of
energy.
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S ECTION 5.2
Energy & Its Forms
O BJECTIVES :
1. Describe the major forms of energy.
Vocabulary:
mechanical energy
thermal energy
conduction
convection
radiation
chemical energy
electric energy
electromagnetic energy
nuclear energy
The major forms of energy are mechanical energy, thermal
energy, chemical energy, electrical energy, electromagnetic
energy, and nuclear energy. Each of these forms of energy can
be converted into other forms of energy.
The energy associated with the motion and position of
everyday objects is mechanical energy. Mechanical energy
is the energy associated with the motion and position of
everyday objects and the sum of an objects potential energy
and kinetic energy. A roller coaster has potential energy at
the top of each hill. Each time that roller coaster moves
downhill, it has kinetic energy. As it moves down the hill it
has both kinetic energy, since it is moving, and potential
energy, since it has the potential to keep moving> The
coaster’s energy keeps changing from kinetic to potential, but
the total mechanical energy stays the same.
The total potential and kinetic energy of all the microscopic
particles or atoms in an object make up its thermal energy.
Tiny particles, or molecules, that make up matter are always
moving the energy created by their movement is called
thermal energy. Thermal energy is the energy of heat.
When an object's atoms move faster, its thermal energy
increases and the object becomes warmer. Thermal energy
passes hear from one object to anther. Thermal energy can be
passed from one object to another. Heat always passes from a
hotter object to a cooler object. The heat energy makes the
molecules in the cooler object more faster. Heat can be
passed three ways: conduction, convection, and radiation.
Heat passes through solids by conduction. When one object
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passes to another by conduction, the heat keeps flowing until
both objects are equally hot. Convection is the way heat
passes through liquids and gases. Molecules in liquids and
gases move apart when they are heated. Radiation moves in
waves. Solar heat comes to you in radiation or
electromagnetic energy.
Chemical energy is the energy stored in chemical bonds.
When bonds are broken, the released energy can do work.
When there is a chemical reaction, the bonds break and
chemical energy is released. All chemical compounds,
including fuels such as coal and gasoline, store energy.
Gasoline has chemical energy. When gasoline is burned in a
car’s engine, the chemical energy is changed to mechanical
energy. The mechanical energy moves the car. Wood released
stored chemical energy when it is burned.
energy that travels through space in the form of waves.
Radiation is electromagnetic energy. Electromagnetic energy
can move through empty space. All the energy in the world
comes from the sun. The sun’s energy is called solar energy.
Solar energy is a type of electromagnetic energy On Earth,
solar energy is changed to other kinds of energy. Nothing on
Earth could live without energy from the sun.
The nucleus of an atom is held together by strong and weak
nuclear forces, which can store an enormous amount of
potential energy. The energy stored in atomic nuclei is known
as nuclear energy. Nuclear energy is given off when the
nucleus breaks apart or fuses with the nucleus of another
atom. Nuclear energy is produced in nuclear power plants.
Many devices you use every day use electricity, or electrical
energy. The particles in matter have positive and negative
charges. Electrons are the negatively charged particles. The
movement of electrons produces electrical energy.
Electrical energy is the energy associated with electric
charges. Electric charges can exert forces that do work. The
wires in home carry electrical energy. Electrical energy makes
light bulbs light up and radios play. Lightning is a form of
electrical energy.
The sun radiates electromagnetic energy into space and is the
source, either directly or indirectly, of most of the world's
energy supplies. Electromagnetic energy is a form of
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Section Review:
1. When you heat a pot of water over a flame, what form of
energy is added to the water?
2.Give an example of each form of energy.
3. When you eat food, which form of energy are you
getting?
4.Which form of energy travels through space in the form
of waves?
5. Which form of energy increases as atoms within an object
move faster?
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S ECTION 5.3
Converting Energy
Energy cannot be created or destroyed, but it can be
converted from one form to another. The process of changing
energy from one form to another is energy conversion.
Energy conversions are constantly taking place all around
you, often without you noticing. Energy from the sun, or solar
energy, travels as light, or electromagnetic energy, to Earth.
Green plants trap light energy and change it into chemical
energy. When an animal eats the plants, the chemical energy
is released.
When energy changes from one form to another, the total
energy remains unchanged even though many energy
conversions may occur. This is one of the most important
concepts in science, the law of conservation of energy. The
law of conservation of energy states that energy cannot
be created or destroyed. According to the law of conservation
of energy, energy can be converted from one form to another.
O BJECTIVES :
1. Describe the law of conservation of energy.
Vocabulary:
energy conversion
law of conservation of energy
One of the most common energy conversions is between
potential energy and kinetic energy. The gravitational
potential energy of an object is converted to the kinetic energy
of motion as the object falls.
Physicist Albert Einstein (1879–1955) developed his special
theory of relativity in 1905. This theory included the nowfamous equation E = mc2. In Einstein's equation, E is energy,
m is mass, and c is the speed of light. E = mc2 says that energy
and mass are equivalent and can be converted into each other.
In other words, energy is released as matter is destroyed, and
matter can be created from energy.
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Section Review:
1. What happens to the total amount of energy as it changes
from one form to another?
2.What is the law of conservation of energy?
3. What is the most common energy conservation?
4.What does E = mc2 say about energy and mass?
5. In the equation E = mc2, what does the c represent?
6.What happens when matter is destroyed?
7. Can matter be created from energy?
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S ECTION 4
Conserving Energy
O BJECTIVES :
1. Classify renewable and nonrenewable energy
resources.
Vocabulary:
nonrenewable energy
fossil fuels
nuclear fission
nuclear fusion
renewable energy
hydroelectric energy
turbine
generator
solar energy
geothermal
wind energy
Most of Earth’s resources are used as energy resources.
Energy is used for transportation, manufacturing, and
countless other things that are important to life as we know it.
Energy resources can be classified as either nonrenewable or
renewable.
Nonrenewable energy resources exist in limited quantities
and, once used, cannot be replaced except over the course of
millions of years. Nonrenewable energy resources include oil, natural gas, coal,
and nuclear energy. Such resources are currently being used
much faster than they can be replaced, creating concern about
how long they will last.
Some of the most important nonrenewable resources are
buried within the Earth’s curst and are know as fossil fuels.
Oil, natural gas, and coal are known as fossil fuels because
they were formed underground from the remains of onceliving organisms. Fossil fuels consist primarily of compounds
of carbon and hydrogen. These compounds contain stored
energy originally obtained from the sunlight by plants and
animals that lived millions of year ago. Currently, fossil fuels
account for the great majority of the world's energy use.
Energy that is produced by bombarding atomic nuclei with
high energy particles is called nuclear energy. One form of
nuclear energy is produced by splitting the nuclei of heavy
atoms, like uranium, is called nuclear fission. Nuclear
power plants use nuclear fission and burn not fossil fuels or
produce no air pollution. However, nuclear fission produces
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radioactive materials. Radiation an make people very sick.
All of the energy that reaches Earth from the sun is produced
by nuclear fusion. During nuclear fusion, the nuclei of
hydrogen atoms combine to form larger nuclei of helium and
releases energy.
Renewable energy resources are resources that can be
replaced in a relatively short period of time. Most renewable
energy resources originate either directly or indirectly from
the sun. The sun and Earth are constantly releasing large
amounts of energy. This energy could be used for generating
electric power, heating buildings, or other purposes.
Renewable energy resources include hydroelectric, solar,
geothermal, wind, biomass, and, possibly in the future,
nuclear fusion. The challenge for engineers and scientists is to
find efficient ways to make these energy resources inexpensive
and convenient.
One of the oldest sources of energy comes from moving water.
Hydroelectric energy is energy obtained from flowing
water. As water flows downhill, its gravitational potential
energy is converted into kinetic energy. This kinetic energy
can be used to turn turbines that are connected to electric
generators. A turbine is like a waterwheel, but turns very
fast. A generator makes electricity. Most hydroelectric
power plants rely on natural flow of water in a river. But most
modern power plants rely on dams across rivers. The major
advantages of hydroelectric energy include its low cost to
produce and lack of pollution; however, dams cause a variety
of environmental problems.
Another source of renewable energy is the sun. Solar
energy is the sun’s energy converted into usable energy.
Solar energy can be collected by passive systems or active
systems. The benefits of solar energy depends on the climate.
Solar energy is nonpolluting, but for areas where cloudy days
are frequent, solar energy is less practical.
Geothermal is the heat from beneath Earth’s surface. Water
is pumped into the ground, where it turns into steam then
drives a generator. Geothermal energy is nonpolluting, but is
not widely available.
Wind is the movement of air over Earth’s surface. Wind
results from air pressure differences caused by the sun’s
uneven heating of the Earth’s surface. Wind energy is
energy obtained from the movement of wind. Wind turbines
converts the kinetic energy into electric energy using the
turbine and generator. Wind energy does not pollute;
however, area with little wind cannot benefit from it.
Fossil fuel supplies may become increasingly scarce and
expensive in the future. An important way to make these
energy resources last longer is to use them more slowly. Energy resources can be conserved by reducing energy needs
and by increasing the efficiency of energy use. Finding ways to
use less energy or to use energy more efficiently is known as
energy conservation.
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People can reduce the use of these resources by making
energy-saving decisions, for example turning off lights when
they are not being used. Because cars consume an enormous
amount of energy, the decisions that people make about
transportation are very important. Walking or biking on short
trips and carpooling can save considerable energy.
Making appliances, cars, and even light bulbs more energy
efficient is a way of reducing energy use while still enjoying its
benefits. Much has already been done to make appliances
more energy efficient. Light bulbs have been developed that
provide superior lighting at a lower energy cost. The
technology for further improvement, including more fuelefficient cars, is already known in many cases.
Section Review:
1. What resources are considered nonrenewable?
2.What is the concern about nonrenewable resources?
3. What are fossil fuels?
4.What resources are considered renewable?
5. Which energy resource would be best used in the dessert?
Why?
6.How can you conserve energy?
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