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Chapter 9
Energy: Forms and Changes
Section 1:
What is
Energy?
Essential questions



What is the relationship between
energy and work?
What is the difference between
kinetic and potential energy?
Identify the different forms of
energy and tell about each one.
Nature of Energy
 Energy
is all around you!
You can hear energy as sound.
 You can see energy as light.
 And you can feel it as wind.

Nature of Energy

You use energy
when you:



hit a softball.
lift your book
bag.
compress a
spring.
Nature of Energy
Living organisms need
energy for growth and
movement.
Nature of Energy

Energy is involved
when:




a bird flies.
a bomb explodes.
rain falls from the
sky.
electricity flows in
a wire.
Nature of Energy

What is energy that it can be
involved in so many different
activities?
 Energy can be defined as the
ability to do work.
 If an object or organism does
work (exerts a force over a
distance to move an object) the
object or organism uses energy.
Nature of Energy
 Because
of the direct
connection between energy and
work, energy is measured in
the same unit as work: joules
(J).
 In addition to using energy to
do work, objects gain energy
because work is being done on
them.
States of Energy:
Kinetic and Potential Energy
Kinetic
Energy is the
energy of motion.
Potential Energy is
stored energy.
Mechanical energy is
potential energy +
kinetic energy.
Kinetic Energy




The energy of motion is called
kinetic energy.
The faster an object moves, the
more kinetic energy it has.
The greater the mass of a moving
object, the more kinetic energy it
has.
Kinetic energy depends on both
mass and velocity.
Kinetic Energy

Kinetic Energy = mass times velocity
squared divided by two
K.E. = mass x velocity
2
What has a greater affect on kinetic
energy, mass or velocity? Why?
Potential Energy

Potential Energy is stored energy.


Stored chemically in fuel, the nucleus
of atom, and in foods.
Or stored because of the work done on
it:
Stretching a rubber band.
 Winding a watch.
 Pulling back on a bow’s arrow.
 Lifting a brick high in the air.

Types of Potential Energy

There are 3 types of Potential
Energy



Gravitational
Elastic
Chemical
Gravitational Potential Energy

Potential energy
that is dependent
on height is called
gravitational
potential energy.
Gravitational Potential Energy

A waterfall, a suspension bridge, and a
falling snowflake all have gravitational
potential energy.
Gravitational Potential Energy

If you stand on a
3-meter diving
board, you have 3
times the G.P.E,
than you had on a
1-meter diving
board.
Gravitational Potential Energy


“The bigger they are the harder
they fall” is not just a saying. It’s
true. Objects with more mass have
greater G.P.E.
The formula to find G.P.E. is
G.P.E. = Weight X Height.
Elastic Potential Energy

Energy that is stored due to being
stretched or compressed is called
elastic potential energy.
Chemical Energy
 Chemical
Energy is required to
bond atoms together.
 And when bonds are broken,
energy is released.
 Chemical energy is a form of
potential energy because it
depends on the position and
arrangement of atoms.
Chemical Energy
 Fuel
and food
are forms of
stored
chemical
energy.
Mechanical Energy
 When
work is done to an
object, it acquires energy.
The energy it acquires is
known as mechanical
energy.
 Mechanical energy = potential
energy + kinetic energy
Mechanical Energy
 When
you
kick a
football, you
give
mechanical
energy to the
football to
make it move.
Mechanical Energy
When you throw a
bowling ball, you
give it energy.
When that
bowling ball hits
the pins, some of
the energy is
transferred to the
pins (transfer of
momentum).
Forms of Energy

The other main forms
of energy are:
Thermal (heat)
 Electrical
 Sound
 Light
 Nuclear

Thermal Energy



The internal motion of the atoms is
called thermal energy, because
moving particles produce heat.
Heat energy can be produced by
friction. Faster the particles move,
the more kinetic energy and the
more heat they produce.
Heat energy causes changes in
temperature and phase of any form
of matter.
Electrical Energy



Power lines carry electromagnetic
energy into your home in the form of
electricity.
Electrical energy is the energy of
moving electrons.
Electrons are negatively charged
particles of atoms.
Sound Energy


Sound energy is caused by a
vibrating object.
The vibrations are transferred
through the air to your ear and your
ear deciphers it.
Light Energy




Light is a form of
electromagnetic energy.
Light energy is produced by
the vibrations of electrically
charged particles.
Each color of light (Roy G
BIV) represents a different
amount of electromagnetic
energy.
Electromagnetic Energy is
also carried by X-rays, radio
waves, and laser light.
Nuclear Energy
 The
nucleus
of an atom is
the source of
nuclear
energy.
Nuclear Energy


When the nucleus splits (fission),
nuclear energy is released in the
form of heat energy and light
energy. Power plants use fission to
generate electrical energy.
Nuclear energy is also released
when nuclei collide at high speeds
and join (fusion).
Nuclear Energy
•The sun’s energy
is produced from
a nuclear fusion
reaction in which
hydrogen nuclei
fuse to form
helium nuclei.
•The sun’s heat
and light come
from fusion.
Nuclear Energy
 Nuclear
energy is the
most
concentrated
form of
energy.
Chapter 9
Energy: Forms and Changes
Section 2:
Energy
Conversions
Essential Questions

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What is an energy conversion?
What are some examples of energy
conversion for the different forms of
energy?
How can energy conversions make
energy useful?
What is the role of machines in
energy conversions?
Energy Conversion

Energy can be changed from one
form to another. These changes are
called energy conversions.
Energy conversions

All forms of energy can be
converted into other forms.


The sun’s energy through solar cells
can be converted directly into
electricity.
Green plants convert the sun’s energy
(electromagnetic) into starches and
sugars (chemical energy).
States of Energy


Most often, the conversion is
between potential and kinetic
energy.
All forms of energy can be in either
of two states:


Potential
Kinetic
Kinetic-Potential Energy Conversion
Roller coasters work because of the energy that is
built into the system. Initially, the cars are pulled
mechanically up the tallest hill, giving them a great
deal of potential energy. From that point, the
conversion between potential and kinetic energy
powers the cars throughout the entire ride.
Kinetic vs. Potential Energy
At the point of maximum potential energy, the car has
minimum kinetic energy.
Kinetic-Potential Energy Conversions

As a basketball
player throws the
ball into the air,
various energy
conversions take
place.
Ball slows down
Ball speeds up
Conversions Involving Chemical Energy


Chemical energy comes from the
food you eat.
Your body uses chemical energy to
function.
Energy Conversions in Living Things

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Photosynthesis uses the sun’s light
energy to create chemical energy
for the plant.
In this way, light energy is changed
into chemical energy.
When you eat, that chemical energy
is converted into kinetic energy for
you to use.
Other energy conversions

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In an electric motor, electromagnetic
energy is converted to mechanical
energy.
In a battery, chemical energy is
converted into electromagnetic energy.
The mechanical energy of a waterfall is
converted to electrical energy in a
generator.
Energy Conversions

In an automobile
engine, fuel is
burned to convert
chemical energy
into heat energy.
The heat energy is
then changed into
mechanical
energy.
Chemical  Heat Mechanical
Who cares?

Energy conversions are needed for
everything we do.
Energy and Machines


Machines make work easier by
changing the size or direction of
force.
Some machines change the energy
put into them into other kinds of
energy.
Review for fun!

Roller coaster energy
Chapter 9
Energy: Forms and Changes
Section 3:
Conservation of
Energy
Essential Questions
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How is energy conserved in a closed
system?
What is the law of conservation of
energy?
What are some examples of how
thermal energy is always a result of
energy conversion?
Why is perpetual motion impossible?
The Law of Conservation of Energy

Energy can be neither created nor
destroyed by ordinary means.


It can only be converted from one form
to another.
If energy seems to disappear, then
scientists look for it – leading to many
important discoveries.
Where Does the Energy Go?


Energy can not be lost.
Roller coaster example: Some of
the potential and kinetic energy is
released as thermal energy because
of FRICTION
A Closed System


A closed system – a group of
objects that transfer energy only to
each other
If all types of energy are added up,
you can see none is lost, just
changed
Law of Conservation of Energy
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Energy cannot be created or
destroyed.
The total amount of energy in a
closed system is always the same.
Any number of conversions could
take place, though.
Thermal Energy


Any time an energy conversion
takes place, some is converted to
thermal energy. This is why there
is no such thing as perpetual
motion.
This thermal energy is due to
FRICTION.
Energy Efficiency

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
Energy efficiency is a comparison
before and after conversion
Energy conversions that waste less
energy are efficient
Aerodynamic cars are an example
Chapter 9
Energy: Forms and Changes
Section 4:
Energy
Resources
Essential Questions

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
What are some energy resources?
How is the sun the source of most
energy on Earth?
What are the advantages and the
disadvantages of using various
energy resources?
Energy resources


Energy resources are natural
resources that can be converted
into other forms of energy to do
work.
Non-renewable resources cannot be
replaced or can only be replaced
very slowly.
Fossil Fuels


Fossil fuels – energy resources
formed from buried plant and
animal remains millions of years
old.
Nonrenewable resources:
petroleum (gasoline, plastics, etc);
natural gas; coal
Electrical Energy from Fossil Fuels

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Fossil fuels are the main source of
electrical energy in the U.S.
Electrical generators convert a fossil
fuels’ chemical energy into electrical
energy
Fossil fuels are burned, thermal
energy turns water to steam, steam
converts to kinetic energy by
powering a turbine, creating
electricity
Nuclear Energy

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Like fossil fuel power plants, nuclear
power plants use thermal energy,
using steam
Nuclear energy is generated from
radioactive elements
Nuclear fission occurs when nuclei
of atoms are split into smaller
nuclei, releasing nuclear energy
Non-renewable resource
Renewable Resources

Renewable resources are replaced
faster than they are used.
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Solar energy (solar cells)
Hydroelectric energy (water-produced)
Wind energy (wind turbines)
Geothermal energy (thermal energy
caused by the heating of the Earth’s
crust)
Biomass (organic matter burned to
release energy)
Non-renewable vs. renewable


Both have advantages and
disadvantages
Copy and study the table on page
262 of the classroom textbook.