Transcript Section 1 What Is Energy?

Chapter 9
Energy and Energy Resources
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Section 1 What Is Energy?
Section 2 Energy Conversions
Section 3 Conservation of Energy
Section 4 Energy Resources
Concept Mapping
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Chapter 9
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).
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Chapter 9
Section 1 What Is Energy?
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Chapter 9
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:
mv 2
kinetic energy =
2
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Chapter 9
Section 1 What Is Energy?
Kinetic Energy
Click below to watch the Visual Concept.
Visual Concept
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Chapter 9
Section 1 What Is Energy?
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Chapter 9
Section 1 What Is Energy?
Potential Energy
• Potential energy is the energy an object has
because of its position.
• Gravitational Potential Energy The amount of
gravitational potential energy that an object has
depends on its weight and its height.
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Chapter 9
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.
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Section 1 What Is Energy?
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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.
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Chapter 9
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
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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.
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Chapter 9
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.
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Section 1 What Is Energy?
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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 potential energy.
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Chapter 9
Section 2 Energy Conversions
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Chapter 9
Section 2 Energy Conversions
Kinetic Energy and Potential Energy,
continued
• Elastic Potential Energy Stretching a rubber band
stores elastic potential energy in the rubber band.
• 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.
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Chapter 9
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.
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Chapter 9
Section 2 Energy Conversions
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Chapter 9
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.
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Chapter 9
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 harness energy
and make that energy work for you.
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Chapter 9
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
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Chapter 9
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 Some machines
help you use energy by converting it into the form of
energy that you need.
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Chapter 9
Section 2 Energy Conversions
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Chapter 9
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.
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Chapter 9
Section 3 Conservation of Energy
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Chapter 9
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.
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Chapter 9
Section 3 Conservation of Energy
Energy Is Conserved Within a Closed System,
continued
• The image below shows energy conservation in a
light bulb.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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Section 4 Energy Resources
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Chapter 9
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.
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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.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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Chapter 9
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.
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