Energy

Energy Changes
1
Energy—What is energy?
• Energy - the ability to cause change or
movement
• Examples:
• energy can change the temperature of a pot of
water
• energy can change the direction and speed of a
baseball.
• https://www.youtube.com/watch?v=_uLSFigtLKg

Energy

• Word “energy” comes from Greek
“energos” which means “active”
• Energy is the ability to cause change
– Can cause a physical change (state of matter)
– Can allow a chemical reaction to occur
• Change in the arrangement of atoms in a molecule

Energy Changes
1 Energy—What is energy?

Examples: continued
• energy in a thunderstorm
produces lightning and
thunder
• energy can change the
arrangement of atoms in
molecules and cause
chemical reactions to occur

Energy Changes
1 Forms of Energy
• Energy comes in different forms from a variety of
sources.
• chemical energy in the
form of food energy
• nuclear energy contained
in the nucleus of the atom
to produce electricity

Types of energy
• Kinetic and potential (mechanical)
All energy is kinetic or potential but there are
different kinds of kinetic and potential
energy
1. Electrical (movement of electrons)
2. Electromagnetic (light/radiation energy)
3. Chemical (energy in chemical bonds)
4. Thermal (heat)
5. Nuclear (energy stored in atoms)
6. Sound energy

Kinetic energy
• The energy an object has due to its motion
• The amount of kinetic energy of an object
depends on its speed and mass
– What is speed
_____________________________
– What is mass
_____________________________
• Higher speed or higher mass = more
kinetic energy
• https://www.youtube.com/watch?v=4CWlNoNpXCc

Energy Changes
1
Energy Transformations
• An energy transformation occurs if energy
changes from one form to another.
• Example:
• energy stored in the
chemical compounds in
your muscles changes to
energy of motion

Energy Changes
1 Energy Transformations: continued
• a car sits in sunlight all day, the energy in
sunlight (radiant energy) changes to heat energy
that warms the inside of the car
• energy used to stretch and move a rubber band
changes into heat energy that raises the
temperature of the rubber band
• During energy transformations:
• the total amount of energy stays the same
• energy is never lost or gained—it only
changes form

Energy Changes
1
Using Energy Transformations
• An electric current in a wire has electrical energy
that can be used in many ways.

Example:
A light bulb converts electrical energy into heat
and light energy when you flip on a switch.

Energy Changes
1
Kinetic Energy (KE)
• kinetic (kih NE tihk) energy (KE) -
the energy an object has due to its
motion
Examples of kinetic energy (KE):
• a moving ball due to its motion
• a football thrown by a quarterback
• a sky diver or a leaf falling toward
Earth

Energy Changes
1 Mass, Speed, and Kinetic Energy (KE)
• moving objects have kinetic energy (KE)
• not all moving objects have the same amount of
kinetic energy
• amount of kinetic energy (KE) an object has
depends on the mass & speed of the object
• Example:
• Mass: a small rock and a large boulder rolling down
a hill at the same speed
• the large boulder could cause more damage – the
large boulder has more kinetic energy
• larger the mass of the object the more kinetic
energy (KE)

Energy Changes
1
Mass, Speed, and Kinetic Energy (KE)
Example:
Speed: The faster a bowling ball moves, the more
pins it can knock down - the more kinetic energy
(KE) it has
• kinetic energy (KE)
increases as speed
increases
• https://www.youtube.com/watch?v=-dpBVtAbKJU

Energy Changes
1
Transferring Kinetic Energy (KE)
• Kinetic energy (KE) can be transferred from one
object to another when they collide.
• Example
• Even if the bowling ball does not touch all of the
pins, it still can knock them all down with one
roll.
• The bowling ball transfers kinetic energy (KE)
to a few pins.
• These pins transfer the kinetic energy (KE) to
the remaining pins and knock them down.

Energy Changes
1
Potential Energy (PE)
• The skier has no kinetic energy (KE) when she is
standing at the top of the hill.
• But as she skis down and moves faster, her
kinetic energy (KE) increases.
• Gravity pulls the skier down the hill.
• When the skier’s position is at the top of the hill,
she has a form of energy called potential energy
(PE).

Potential energy
• Energy stored due to an objects location

Energy Changes
1
• Potential energy (PE) - energy that is stored
because of an object’s position

• http://phet.colorado.edu/sims/energy-skate-
park/energy-skate-park_en.jar

Potential energy
• The potential energy depends on the
location of the object and its mass

Energy Changes
1
• By using the ski lift to take her to the top of the
hill, the skier increased her potential energy (PE)
by changing her position.

Energy Changes
1
Increasing Potential Energy (PE)
• When you raise an object above its original
position, it has the potential to fall.
• If it does fall, it has kinetic energy (KE).
• To raise an object, you have to transfer energy to
the object.
• This energy becomes stored as potential energy
(PE).

Energy Changes
1
Increasing Potential Energy (PE)

• If the object were lifted higher, the potential
energy (PE) would increase.

• The higher an object is lifted above Earth, the
greater its potential energy (PE).

Energy Changes
1
Converting Potential (PE) and
Kinetic Energy (KE)
• Kinetic energy (KE) also can be transformed into
potential energy (PE).
Example:
• Suppose you throw a ball straight up into the air.
• The muscles in your body cause the ball to move
upward when it leaves your hand - an energy
transfer
• the moving ball has kinetic energy (KE)

Energy Changes
1
Converting Potential
and Kinetic Energy
• As the ball gets higher and higher, its potential
energy is increasing.
• At the same time, the
ball is slowing down
and its kinetic energy
(KE) is decreasing.

Energy Changes
1
and Kinetic Energy
• At its highest point, the ball comes to a stop for
an instant before it starts to fall downward
again. Here all the
kinetic energy (KE)
the ball had when it
left your hand has
been converted to
potential energy (PE).

Energy Changes
1
and Kinetic Energy
• As the ball falls downward, its potential energy
(PE) is converted back into kinetic energy (KE).
• If you catch the ball at the same height above
the ground as when you
threw it upward, its
kinetic energy will be
the same as when it left
your hand.

Energy Changes
1
Energy Changes in Falling Water
• Just like a ball falling to the
ground, the potential energy
(PE) that water has at the
top of a waterfall is
transformed into kinetic
energy as it falls downward.

Energy Changes
1
Energy Changes in Falling Water
• The kinetic energy (KE) of falling water can be
used to generate electricity.
• Water backs up behind a dam on a river, forming
a lake or reservoir. (PE)
• The water near the top of the dam then falls
downward. (KE)
• The kinetic energy (KE) of the moving water
spins generators, which produce electricity.
• The potential energy (PE) of the water behind the
dam is transformed into electrical energy.

Conserving energy

• James Joule demonstrated the law of
conservation of energy in 1840
– Law states energy can not be created or
destroyed, just transferred from one form to
another
– The total amount of energy in the universe
stays the same
– Energy is measured in “Jules of work”

Energy Changes
1
Conservation of Energy
• Example:
• Kinetic energy (KE) - converts into heat
energy when two objects rub against each
other
• A book slides across a table - it will slow down
and eventually stop
• The book’s kinetic energy (KE) isn’t lost.
• Its kinetic energy (KE) converted into heat
energy as the book rubs against the surface of
the table.

Energy transformation

• Energy transformation- when energy
changes from one form to another form
– The total amount of energy stays the same,
but the type of energy changes
• Chemical energy in a battery is changed
into kinetic energy

Energy transfer
• When you raise an object, you use kinetic
energy which is transferred into potential
energy (because it has the potential to fall)

Other energy transfers
• A waterfall has potential energy at the top
of the waterfall and kinetic as it falls
• Can convert the kinetic energy into
electrical energy or use the kinetic
energy to move other
things

Energy Changes
1
Following the Energy Trail
• Chemical energy in a soccer player’s leg
muscles is converted into kinetic energy (KE)
when she swings her leg.
• When the ball is kicked - kinetic energy (KE) is
transferred to the ball
• After the ball rolls for a while, it comes to a stop.
• As the ball rolled, its kinetic energy (KE) was
transformed into heat energy as the ball rubbed
against the grass.
http://www.youtube.com/watch?v=_uLSFigtLKg

What is Electrical Energy?
o Energy caused by
the movement of
electrons
o Easily transported
through power lines
and then converted
into other forms of
energy

What is Chemical Energy?

o Energy that can be
released during chemical
reactions.
oEnergy stored in chemical
bonds.

What is Thermal Energy?
• The microscopic kinetic energy
of atoms and molecules
• A measure of how active the
atoms and molecules are.
• A hot object has excited
molecules and atoms that move
fast
• A cooler object has slower
moving molecules and atoms

Temperature
2 Measuring Temperature
• Temperature - related to the kinetic energy (KE)
of all the atoms or molecules in an object
(average kinetic energy)
• Because atoms or molecules are so small and
objects contain so many of them
- it is impossible to measure the
kinetic energy of each individual
atom or molecule
• A practical way to measure
temperature is to use a
thermometer

Temperature
2
The Fahrenheit Scale
• Fahrenheit scale –
• the freezing point of water = 32°F
• the boiling point of water = 212°F
• The space between is divided into
180 equal degrees
• used mainly in the United States

Temperature
2
The Celsius Scale
• Celsius (SEL see us) temperature scale
• the freezing point of water = 0°C
• the boiling point of water = 100°C
• The space between is divided into
100 equal degrees
• used more widely throughout the
world

Temperature = heat
• Temperature and heat are not the same
thing
– Temperature: measure of how hot something
is
– Heat: flow of energy from a hotter object to a
cooler one
• Measuring temperature and heat
– Temperature units: degrees Fahrenheit,
Celsius, Kelvin
– Heat units: Joule, calorie, BTU, kilocalorie

Heat

• Heat: transfer of energy from one object to
another due to a difference in temperature
• Heat flows from warmer object to cooler
one

• Heat transfer doesn’t mean high
temperature (ex heating beaker of ice)

HOT COLD
HEAT

COLD
VERY More HEAT
HOT

Heat transfer

• Heat flows from hotter objects to colder
objects.
• Heat flow depends on the temperature
difference between objects
• Heat is not temperature
• There are thermal insulators and
conductors

More about heat…
• Thermal Conductors
– Materials through which it is easy to transfer
thermal energy
– Metals are the best thermal conductors
• Thermal insulators
– Poor conductors of heat
– Air is a good insulator, therefore, many
insulating materials have air spaces
– Other good insulators are wood, rubber, and
ceramic

Temperature
2 Heat on the Move
• A transfer of energy occurs if there is a
temperature difference between two areas in
contact.
• Heat is always transferred from warm places to
cooler ones.
• Heat transfers can take place in three ways
• conduction
• convection
• radiation

Temperature
2
Heat on the Move

• Conduction transfers heat mainly through solids
and liquids

• Convection transfers heat mainly through liquids
and gases

• Radiation can transfer energy through space and
air

Temperature
2 Conduction
• Conduction (kun DUK shun) - the transfer of
energy by collisions between the atoms in a
material.
• A spoon in boiling water becomes warmer
because its atoms and molecules moved faster
• faster particles then collided
with slower-moving
particles in the colder of the
spoon
• Kinetic energy (KE) is
transferred up the spoon’s
handle.

Temperature
2
Bumping Along
• In a solid, the particles involved don’t travel
from one place to another.
• They simply move back and forth in place,
bumping into their neighbors transferring
energy from faster-moving
particles to slower-moving
ones.
• Conduction usually occurs in
solids.

Temperature
2
Conductors
• thermal conductors - materials through which it
is easy to transfer energy
• Most metals are good conductors of heat.
• Metals such as gold, silver,
and copper are the best
thermal conductors.
• Copper is widely available
and less expensive than gold
or silver.

Temperature
2
Insulators
• Materials made of plastics also are often good
insulators.
• If you put a plastic spoon in
boiling water, it takes a long
time for it to get hot.
• Many cooking pans have plastic
handles that remain at a
comfortable temperature while
the pans are used for cooking.

Temperature
2 Insulators
• thermal insulators - materials that are poor
conductors of heat
• Clothes and blankets -
• poor conductors of heat
• heat cannot escape easily from your body by
trapping your body heat around you
• help keep you warm because they are made of
materials that contain many air spaces.

• Air is a good insulator.

Temperature
2
Convection
• Convection (kun VEK shun) transfers heat
when particles move between areas that differ in
temperature.
• most common in gases and liquids
• As temperature increases, particles move around
more quickly, and the distance between particles
increases.
• This causes density to decrease as temperature
increases.
• Cooler, denser material forces the warmer, less
dense material to move upward.

Temperature
2
Examples of Convection
• Sometimes a bird can stay in the air without
flapping its wings because it is held up by a
thermal.
• A thermal
• column of warm air that is
forced up as cold air
around it sinks
• a convection current in
the air

Temperature
2
Convection
• Some homes are heated by convection.

Temperature
2
Examples of Convection
• Convection also occurs in liquids.
• In a pot of boiling water, the warmer, less dense
water is forced up as the cooler, denser water
sinks.
• Convection currents on a larger scale are
formed in oceans by cold water flowing from
the poles and warm water flowing from tropical
regions.

Temperature
2
Radiation
• radiation (ray dee AY shun) - the transfer of
energy by waves
• radiation waves can be visible light waves or
types of waves that you cannot see
• When radiation waves strike an object - their
energy can be absorbed and the object’s
temperature rises
• Radiation waves can travel through air and
even through a vacuum

Temperature
2
Radiation Examples:
• The Sun transfers energy to Earth through
radiation.
• Heat is transferred by radiation from the fire and
you become warmer. You also can use radiation
to cook food.
• A microwave oven cooks food by using
microwave radiation to transfer energy to the
food.

Convection, conduction, radiation
• Thermal energy passes by conduction,
convection, or radiation
• Conduction – transfer of heat by direct
contact to a solid substance.
Example: the
transfer of
thermal energy
from the metal
bar to your hand.

• Radiation – transfers energy by waves
through empty space. Can be visible light
or other types of radiation (fex microwave,
UV radiation).

Heat

• Convection – transfer of heat energy
between a solid surface and the nearby
liquid or gas in motion
• May create a convection
cell

Convection cell

• Heat rises, cool air sinks
– Why?
• What is density?

Expansion, contraction
• Expansion: as an object is heated up, the atoms
are excited and move more quickly. As they
move more quickly, they move farther and
expand.
– If your balloon deflates, heat it up
• Contraction: as an object cools, the atoms move
more slowly and become closer together. They
contract, or take up a smaller space.
– Which will be more dense? A heated balloon or
cooled one?

Examples

• Which is conduction, convection,
radiation? B
A

C

More on types of energy
• Nonrenewable energy
– Made from nonrenewable sources (sources
that don’t renew themselves as fast as they
are consumed)
• Nuclear, fossil fuels, natural gas
• These are created naturally but take millions of
years to form and we use them much more quickly
than they form.

More on energy

• Renewable energy
– Made from renewable sources (can be
replenished naturally at same rate or faster
than they are consumed)
• Solar, wind, tidal, wave, hydroelectric, geothermal,
bio-fuel
• Some renewable sources are not as good as
others…
– Discuss downside of biofuel

• http://www.youtube.com/watch?v=_uLSFigtLKg

• http://www.youtube.com/watch?v=qybUFnY7Y8w

Section Check
1
Question 1
What is energy?

Answer
Energy is the ability to cause change. An
object that has energy can do something or
make something happen.

Section Check
1
Question 2
A book resting on top of a bookshelf has no
kinetic energy. It does, however, have _______
energy.

A. chemical
B. mechanical
C. negative
D. potential

Section Check
1
Answer
The answer is D. If the book falls, its potential
energy will be replaced by kinetic energy.

Section Check
1
Question 3
As the mass of a moving object increases, its
kinetic energy _______.

A. decreases
B. increases
C. stays constant
D. terminates

Section Check
1
Answer
The answer is B.

Section Check
2
Question 1
The two most common temperature scales are
the _______ and the _______ scale.

A. absolute and Kelvin
B. Fahrenheit and Kelvin
C. Fahrenheit and Celsius
D. Kelvin and Celsius

Section Check
2
Answer
The answer is C. In science you will also
encounter the Kelvin scale but it is not
commonly used in everyday temperature
readings.

Section Check
2
Question 2
Explain how temperature is related to the
motion of molecules in a material.

Answer
Temperature is a measure of the average value
of the kinetic energy of the molecules in a
substance.

Section Check
12-2
Question 3
How are temperature and pressure
related?

Section Check
12-2 Answer
When air is heated, its molecules move faster
and the air expands
This makes the air less dense and it rises.
As this less dense air rises and exerts less
pressure on anything below it.
Cooled air becomes denser and sinks as the
molecules slow down and move closer
together.
This cool air exerts more pressure on anything
below it.

Section Check
2
Question 4
Heat can move from place to place in different
ways. When heat moves from one object to
another as a result of direct contact, the process
is known as _______.

A. conduction
B. convection
C. radiation
D. thermal transfer

Section Check
2
Answer
The answer is A. An everyday example of
conduction occurs when you pick up a cup of
coffee and feel the warmth in your fingers.

Chemical Energy
3
Chemical Reactions and Energy—
What is a chemical reaction?
• In a chemical reaction-
• compounds - broken down
• new compounds - formed

Chemical Energy
3
Energy in Reactions
• After the hydrogen and oxygen atoms are
bound together to form a water molecule, it is
difficult to split them apart.

• Energy—usually supplied by electricity, heat, or
light—is required to break the chemical bonds.

Chemical Energy
3
Energy-Absorbing Reactions
• Some chemical reactions need a constant supply
of energy to keep them going. These reactions
absorb energy. A chemical reaction that absorbs
heat energy is called an endothermic (en duh
THUR mihk) reaction.
• Examples:
• preparation of food
• photosynthesis

Chemical Energy
3
Energy-Absorbing Reactions
(endothermic chemical reaction)
• Chemical reactions occur when sunlight strikes
the leaves of green plants.
• These chemical reactions convert the energy in
sunlight into chemical energy contained in a
type of sugar. Oxygen also is produced by
these chemical reactions.
• When the plant is deprived of sunlight, the
reactions stop.

Chemical Energy
3 Energy-Absorbing Reactions
• This process is
called
photosynthesis
.

Chemical Energy
3
Energy-Releasing Reactions
• Endothermic chemical reactions are usually
important because of the compounds the
reactions produce.
• Other reactions are important because they
release energy.
• Exothermic (ek soh THUR mihk) reactions
are chemical reactions that release heat
energy.

Chemical Energy
3 Energy-Releasing Reactions
• When a substance burns, atoms in the
substance combine with oxygen atoms in
the air.
• An exothermic reaction
occurs & energy in the
form of heat and light is
released.
• The exothermic reaction that occurs when a
material burns by combining with oxygen is
called combustion.

Chemical Energy
3
Rate of Reaction

• Chemical reactions can occur at different rates.
Examples:
• fireworks explode -
very fast chemical
reaction rate
• rust - very slow
chemical reaction
rate

Chemical Energy
3 Changing the Rate of Reaction
• Two ways to change the rate of a chemical
reaction are:
• changing the temperature
• adding a type of compound called a catalyst
• A catalyst (KA tuh list) - a substance that
changes the rate of a chemical reaction
without any permanent change to its own
structure.
• enzymes – protein catalysts that control
many cell processes in your body

Chemical Energy
3
Changing the Rate of Reaction

• Enzymes are found
throughout your body and
are important for growth,
respiration, & digestion.

Chemical Energy
3
Changing the Rate of Reaction
• When you chew a piece of
bread, glands in your
mouth produce saliva that
contains an enzyme
(amylase).
• The enzyme in saliva acts
as a catalyst to help break
down starches in food into
smaller molecules.

Section Check
3
Question 1
A substance that speeds up a chemical reaction
is known as a _______

Section Check
3
Answer
A catalyst can be added to speed up a
chemical reaction. A catalyst changes the
rate of a chemical reaction without any
permanent change to its own structure.

Section Check
3
Question 2
What occurs when a chemical compound is
broken apart?

Section Check
3
Answer
When a chemical compound is broken apart,
the bonds between the atoms that make up the
compound are broken.

Section Check
3
Question 3
Where is the energy stored in a compound?

Answer
Energy is stored in the bonds between the
atoms. In order to release that energy the bonds
must be broken.

Reviewing Main Ideas
1
Energy Changes
• Energy is the ability to cause change.
• Energy can have different forms. Energy can
be transformed from one form into another.
• Kinetic energy is the energy an object has
due to its motion. Kinetic energy increases as
the speed of an object increases.
• Potential energy is stored energy that
increases as an object’s height increases.

2
Temperature

• Temperature is a measure of the average
kinetic energy of the particles in a material.

• The movement of energy from a warmer
object to a cooler one is called heat.

• Heat can be transferred by conduction,
convection, and radiation.

3
Chemical Energy
• The energy stored in chemical bonds is
chemical energy.
• Chemical reactions can release or absorb
energy. Exothermic reactions are chemical
reactions that release energy. Endothermic
reactions absorb energy.
• Changing the temperature and adding
catalysts can change the rate of chemical
reactions.

Chapter Review

Question 1
Why does convection usually occur in liquids
and gases, but not in solids?

Chapter Review

Answer
In liquids and gases, atoms and molecules are
free to move from place to place. As a result,
they can transfer energy by moving from a
warmer place to a cooler place in a material. In
solids, atoms and molecules don’t move from
place to place within the solid.

Chapter Review

Question 2
In an exothermic reaction, heat energy is
_______.

A. absorbed
B. created
C. destroyed
D. released

Chapter Review

Answer
The answer is D. Exothermic reactions release
heat energy.

Chapter Review

Question 3
How does the Sun’s energy reach Earth?

Answer
The Sun’s energy reached Earth by radiation.
The other forms of heat transfer can’t occur
through empty space.

Chapter Review

Question 4
One of the reasons the handle of a pan is made
of wood rather than metal is that wood does not
transfer heat as quickly from the hot pan to your
hand. In other words, wood is a poor _______.

A. conductor
B. coolant
C. insulator
D. thermometer

Chapter Review

Answer
The answer is A. Wood is a poor conductor of
heat energy.

Chapter Review

Question 5
Chemical energy is a form of which type of
energy?

A. kinetic energy
B. nuclear energy
C. heat energy
D. potential energy

Chapter Review

Answer
The answer is D. Chemical energy is a form of
potential energy that is stored in the binds
between atoms in a compound.

Standardized Test Practice

Question 1
Burning is a(n) _______ chemical reaction.

A. endothermic
B. exothermic
C. photosynthesis
D. kinetic


Answer
The answer is B. Because heat is released, the
chemical reaction is exothermic.


Question 2
The temperature of a material increases when
the atoms in the material _____.

A. move closer together
B. move farther apart
C. move faster
D. move slower


Answer
The answer is C. When temperature increases,
the atoms are moving faster and have more
kinetic energy.


Question 3
As the height of a ball increases, its _____
energy increases.

A. kinetic
B. electrical
C. heat
D. potential


Answer
The answer is D. When the height of an object
increases, its potential energy increases.


Question 4
As water falls from the top of a waterfall, which
forms of energy are changing?

A. electrical and chemical
B. kinetic and potential
C. kinetic and electrical
D. potential and nuclear


Answer
The correct answer is A. Kinetic energy is
the energy of motion.


Question 5
What determines the kinetic energy of an
object?

A. only its mass
B. only its speed
C. both its mass and speed
D. both its mass and speed as well as its
direction


Answer
The answer is C. Mass and speed are the two
factors you need to know to determine the
kinetic energy of an object.

Energy

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