Transcript Section 1 What Is Energy?

Chapter 12
Energy and Energy Resources
Preview
Section 1 What Is Energy?
Section 2 Energy Conversions
Section 3 Conservation of Energy
Section 4 Energy Resources
Concept Mapping
Chapter 12
Section 1 What Is Energy?
Bellringer
Finish the following phrase:
“Energy is the ability to ____.”
Write your completed phrase in your science journal.
People often use the words energy and power
synonymously, but they have specific meanings.
What is the distinction between energy and power?
Chapter 12
Section 1 What Is Energy?
Objectives
• Explain the relationship between energy and work.
• Compare kinetic energy and potential energy.
• Describe the different forms of energy.
Chapter 12
Section 1 What Is Energy?
Energy and Work: Working Together
• Energy is the ability to do work.
• Work is done when a force causes an object to move
in the direction of the force. Work is a transfer of
energy.
• Energy and work are expressed in units of joules (J).
Chapter 12
Section 1 What Is Energy?
Chapter 12
Section 1 What Is Energy?
Kinetic Energy
• Kinetic energy is the energy of motion. All moving
objects have kinetic energy.
• Kinetic Energy Depends on Mass and Speed If
you know an object’s mass (m) and its speed (v), you
can calculate the object’s kinetic energy with the
following equation:
kinetic energy =
mv 2
2
Chapter 12
Section 1 What Is Energy?
Kinetic Energy
Click below to watch the Visual Concept.
Visual Concept
Chapter 12
Section 1 What Is Energy?
Chapter 12
Section 1 What Is Energy?
Potential Energy
• Potential energy is the energy an object has
because of its position.
• Elastic potential energy can be stored in objects
like bowstrings, springs, and rubber bands. The energy
put into stretching becomes elastic potential energy.
• Gravitational Potential Energy The amount of
gravitational potential energy that an object has
depends on its weight and its height.
Chapter 12
Section 1 What Is Energy?
Potential Energy, continued
• Calculating Gravitational Potential Energy The
equation to find gravitational potential energy is:
gravitational potential energy = weight  height
• Gravitational potential energy is equal to the amount
of work done on an object to lift it a certain height.
Chapter 12
Section 1 What Is Energy?
Potential Energy, continued
• Height Above What? When you find out an
object’s gravitational potential energy, the “ground”
that you measure the object’s height from depends
on where it is.
• The height you use in calculating gravitational
potential energy is a measure of how far an object
has to fall.
Chapter 12
Section 1 What Is Energy?
Chapter 12
Section 1 What Is Energy?
Mechanical Energy
• Mechanical energy is the total energy of motion and
position of an object. Both kinetic energy and potential
energy are kinds of mechanical energy.
• The equation to find mechanical energy is:
mechanical energy = potential energy  kinetic energy
Chapter 12
Section 1 What Is Energy?
Mechanical Energy, continued
• The mechanical energy of an object remains the
same unless it transfers some energy to another
object.
• But even if the mechanical energy of an object stays
the same, the potential energy or kinetic energy can
increase or decrease.
Chapter 12
Section 1 What Is Energy?
Other Forms of Energy
• Thermal Energy is all of the kinetic energy due to
random motion of the particles that make up an object.
• All matter is made up of particles that are always in
random motion. So, all matter has thermal energy.
• Thermal energy increases as temperature increases
and increases as the number of particles increases.
Chapter 12
Section 1 What Is Energy?
Chapter 12
Section 1 What Is Energy?
Other Forms of Energy, continued
• Chemical Energy is the energy of a chemical
compound that changes as its atoms are rearranged.
• Chemical energy is a form of potential energy
because it depends on the position and arrangement
of the atoms in a compound.
• The energy in food is chemical energy.
Chapter 12
Section 1 What Is Energy?
Other Forms of Energy, continued
• Electrical Energy is the energy of moving electrons.
Electrical energy can be thought of as potential energy
that is used when you plug in an electrical appliance
and use it.
• Sound Energy is caused by an object’s vibrations.
The object’s vibrations transmit some kinetic energy to
the air particles, which also vibrate. These vibrations
transmit sound energy.
Chapter 12
Section 1 What Is Energy?
Other Forms of Energy, continued
• Light Energy is produced by the vibrations of
electrically charged particles.
• Nuclear Energy is energy that comes from changes
in the nucleus of an atom. Nuclear energy can be
produced when nuclei are joined in a fusion reaction or
when a nucleus is split apart in a fission reaction.
Chapter 12
Section 2 Energy Conversions
Bellringer
What do the following objects have in common: a
plant, a Bunsen burner, a pendulum. Can you think of
three more objects that have same the common link?
Record your guesses in your science journal.
Chapter 12
Section 2 Energy Conversions
Objectives
• Describe an energy conversion.
• Give examples of energy conversions for the different
forms of energy.
• Explain how energy conversions make energy
useful.
• Explain the role of machines in energy conversions.
Chapter 12
Section 2 Energy Conversions
Kinetic Energy and Potential Energy
• An energy conversion is a change from one form of
energy to another. Any form of energy can change into
any other form of energy.
• As the skateboarder on the next slide travels up and
down the half-pipe, his energy changes back and forth
between kinetic energy and gravitational potential
energy.
Chapter 12
Section 2 Energy Conversions
Chapter 12
Section 2 Energy Conversions
Kinetic Energy and Potential Energy,
continued
• Elastic Potential Energy The energy you put into
stretching the rubber band becomes elastic potential
energy.
• When you let the rubber band go, it goes back to its
original shape. It releases its stored-up potential
energy as it does so.
• There is also increased kinetic energy of air particles
as the propeller pushes on them.
Chapter 12
Section 2 Energy Conversions
Conversions Involving Chemical Energy
• Chemical energy is stored in the food you eat. Your
body uses this chemical energy to function.
• Energy Conversion in Plants The chemical energy
in the food you eat comes from the sun’s energy.
Plants use photosynthesis to convert light energy into
chemical energy, as shown on the next slide.
Chapter 12
Section 2 Energy Conversions
Chapter 12
Section 2 Energy Conversions
Conversions Involving Chemical Energy,
continued
• The Process Continues Plants change light energy
into chemical energy. The chemical energy in the food
you eat is changed into another kind of chemical
energy that your body can use.
• Your body then uses that energy to give you kinetic
energy that you use in everything you do.
Chapter 12
Section 2 Energy Conversions
Why Energy Conversions Are Important
• Energy conversions are needed for everything we do.
Heating our homes, getting energy from a meal, and
many other things use energy conversions.
• Machines, such as a hair dryer, help convert energy
and make that energy work for you.
Chapter 12
Section 2 Energy Conversions
Why Energy Conversions Are Important,
continued
• Conversions Involving Electrical Energy Some
common energy conversions that involve electrical
energy are shown in the table below.
Alarm clock electrical energy  light and sound energy
Battery
chemical energy  electrical energy
Light bulb
electrical energy  light and thermal energy
Blender
electrical energy  kinetic and sound energy
Chapter 12
Section 2 Energy Conversions
Energy and Machines
• A machine can make work easier by changing the
size or direction (or both) of the force needed to do the
work. Some machines allow you to use less force over
a greater distance to do the same amount of work.
• Machines as Energy Converters Machines help
you use energy by converting into the form that you
need.
Chapter 12
Section 2 Energy Conversions
Chapter 12
Section 3 Conservation of Energy
Bellringer
Where does the energy come from to make a roller
coaster car move? Where does all the energy go?
Explain the meaning of the sentence, “All of the
energy put into a process still exists somewhere at
the end of that process.”
Use the roller coaster example to illustrate your
explanation in your science journal.
Chapter 12
Section 3 Conservation of Energy
Objectives
• Explain how energy is conserved within a closed
system.
• Explain the law of conservation of energy.
• Give examples of how thermal energy is always a
result of energy conversion.
• Explain why perpetual motion is impossible.
Chapter 12
Section 3 Conservation of Energy
Where Does the Energy Go?
• Friction is a force that oppose motion between two
surfaces that are touching.
• For a roller coaster car to move, energy must be
used to overcome the friction between the car’s wheels
and the track.
• As a result, not all of the car’s potential energy
changes into kinetic energy and not all of the car’s
kinetic energy changes back into potential energy.
Chapter 12
Section 3 Conservation of Energy
Chapter 12
Section 3 Conservation of Energy
Energy Is Conserved Within a Closed System
• A closed system is a group of objects that transfer
energy only to each other.
• The Law of Conservation of Energy states that
energy cannot be created or destroyed.
• Energy can be converted from one form to another.
But all of the different forms of energy in a system
always add up to the same total amount of energy.
Chapter 12
Section 3 Conservation of Energy
Energy Is Conserved Within a Closed System,
continued
• The image below shows energy conservation in a
light bulb.
Chapter 12
Section 3 Conservation of Energy
No Conversion Without Thermal Energy
• Any time one form of energy is converted into another
form, some of the original energy always gets
converted into thermal energy.
• The thermal energy due to friction that results from
energy conversions is not usually useful energy.
Chapter 12
Section 3 Conservation of Energy
No Conversion Without Thermal Energy,
continued
• Perpetual Motion? No Way! A perpetual motion
machine is a machine that would run forever without
any additional energy.
• But perpetual motion machines are impossible
because some waste thermal energy always results
from energy conversions.
Chapter 12
Section 3 Conservation of Energy
No Conversion Without Thermal Energy,
continued
• Making Conversions Efficient Some systems
transform energy with less loss of heat than others do.
Such systems are more efficient than others are.
• Improving the efficiency of machines is important
because greater efficiency results in less waste. If less
energy is wasted, less energy is needed to operate a
machine.
Chapter 12
Section 4 Energy Resources
Bellringer
Write the names of several different energy
resources in your science journal. Predict which
ones are nonrenewable (a finite supply) and
renewable (an endless supply) resources.
Chapter 12
Section 4 Energy Resources
Objectives
• Name several energy resources.
• Explain how the sun is the source of most energy
on Earth.
• Evaluate the advantages and disadvantages of
using various energy resources.
Chapter 12
Section 4 Energy Resources
Nonrenewable Resources
• Nonrenewable resources cannot be replaced or are
replaced much more slowly than they are used.
• Fossil fuels are nonrenewable energy resources that
formed from the remains of organisms that lived long
ago. Oil, natural gas, and coal are the most common
fossil fuels.
Chapter 12
Section 4 Energy Resources
Chapter 12
Section 4 Energy Resources
Nonrenewable Resources, continued
• Uses of Fossil Fuels All fossil fuels contain stored
energy from the sun, which can be converted into
other kinds of energy.
• Burning coal is a common way to generate electrical
energy. Petroleum is used to make gasoline, wax, and
plastics. Natural gas is often used in home heating.
Chapter 12
Section 4 Energy Resources
Nonrenewable Resources, continued
• Electrical Energy from Fossil Fuels Electric
generators convert the chemical energy in fossil fuels
into electrical energy by the process shown below.
Chapter 12
Section 4 Energy Resources
Nonrenewable Resources, continued
• Nuclear Energy Another way to generate electrical
energy is to use nuclear energy.
• In a process called nuclear fission, the nucleus of a
radioactive atom is split into two smaller nuclei, which
releases nuclear energy.
• Because the supply of radioactive elements is limited,
nuclear energy is a nonrenewable resource.
Chapter 12
Section 4 Energy Resources
Renewable Resources
• Renewable resources are naturally replaced more
quickly than they are used.
• Solar Energy Sunlight can be changed into
electrical energy through solar cells.
• Solar cells can be used in devices such as
calculators. They can also be placed on the roof of a
house to provide electrical energy.
Chapter 12
Section 4 Energy Resources
Renewable Resources, continued
• Energy from Water The potential energy of water in
a reservoir can be changed into kinetic energy as the
water flows through a dam.
• In a hydroelectric dam, falling water turns turbines.
The turbines are connected to a generator that
changes kinetic energy into electrical energy.
Chapter 12
Section 4 Energy Resources
Renewable Resources, continued
• Wind Energy The kinetic energy of wind can turn
the blades of a windmill or a wind turbine.
• A wind turbine changes the kinetic energy of the air
into electrical energy by turning a generator.
Chapter 12
Section 4 Energy Resources
Renewable Resources, continued
• Geothermal Energy is thermal energy caused by the
heating of Earth’s crust. This energy can be converted
into electrical energy at geothermal power plants.
• Biomass is organic matter, such as plants, wood,
and waste, that can be burned to release energy.
Some countries depend on biomass for energy.
Chapter 12
Section 4 Energy Resources
The Two Sides to Energy Resources
• All energy resources have advantages and
disadvantages. Many factors determine when one
energy source is a better choice than another.
• Choosing the Right Energy Source Energy
planning in all parts of the world requires careful
consideration of energy needs and the availability and
responsible use of resources.
Chapter 12
Energy and Energy Resources
Concept Mapping
Use the terms below to complete the concept map
on the next slide.
potential energy
position
mechanical energy
motion
kinetic energy
mass
machines
Chapter 12
Energy and Energy Resources
Chapter 12
Energy and Energy Resources