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th
7
Grade Energy Unit
Chapter Five, Section One
What is Energy?
What is Work?
• Work is done on an object when the object moves in the same
direction in which the force is exerted.
Requirements for work to occur:
1.
2.
Object that the force is being applied to has to move
Force is in the same direction as the object moving.
Object is moving in the
same direction as the
force.
Energy, Work, and Power
• The ability to do work or cause a change is called energy.
What are some examples of work that you have done today?
Work and Energy
• When one thing does work on another some of its energy is
transferred to that object.
Work and Energy
• In other words, work is the transfer of energy.
• The object which the work is done upon gains energy.
• Energy is measured in JOULES (J)
• http://www.brainpop.com/science/motionsforcesandtime/work/p
review.weml
What is the origin of all energy?
•THE ORIGIN OF ALL
ENERGY IS THE SUN AND
THE EARTH’S CORE
Kinetic Energy
• Two basic kinds of energy are:
1. Kinetic energy
2. Potential energy
•
To determine if energy is potential or kinetic, you must first
determine if the object is in motion.
Kinetic Energy
Kinetic Energy
• Because the moving object does work, it has energy.
• The energy that an object has due to its motion is called kinetic
energy
• The word kinetic comes from the Greek word kinetos, which
means moving.
• http://www.brainpop.com/science/energy/kineticenergy/preview
.weml
Factors Affecting Kinetic Energy
• There are two main factors that affect the amount of kinetic
energy that an object has:
1. Mass
2. Velocity
Which rock would have the greater amount
of kinetic energy when rolled down a hill?
Factors Affecting Kinetic Energy
Factor
How the Kinetic Energy is Affected
Increase in Mass
Increases the amount of Kinetic Energy
Decrease in Mass
Decreases the amount of Kinetic Energy
Increase in Velocity
Increases the amount of Kinetic Energy
Decrease in Velocity
Decreases the amount of Kinetic Energy
A Good Hint
• If you do not know the mass and velocity of an object and want to
know if it has a lot of a little kinetic velocity, ask yourself the
following question:
“How hard would it be to stop the object from moving?”
• The harder it is to stop an object from moving the more kinetic
energy it is going to have.
Calculating Kinetic Energy
Kinetic Energy = ½ × Mass × Velocity²
• The formula above means that Mass and Velocity do not have the
same effect on the kinetic energy of an object.
• The velocity will have a greater impact than the mass of the
object.
Potential Energy
• The second basic type of energy is Potential Energy
• Stored energy that results from the position or shape of an object
is called potential energy.
• This type of energy has the potential to do work.
Potential Energy
• There are two main divisions of potential energy:
• Gravitational Potential Energy
• Elastic Potential Energy
http://www.brainpop.com/science/energy/potentialenergy/preview.weml
Forms of Energy
Chapter Five, Section Two
Types of Potential Energy
Potential Energy is stored Energy
1.
2.
3.
4.
Gravitational Potential Energy
Elastic Potential Energy
Chemical Energy
Nuclear Energy
Gravitational Potential Energy
• Potential Energy that is related to an object’s height is called
gravitational potential energy.
• Gravitational potential energy = do the work needed to lift it
Gravitational Potential Energy = Weight × Height
Gravitational Potential Energy
• Examples of Gravitational Potential Energy:
1. Rollercoaster at the top of the hill
2. Water being held back by a dam
3. Rock on the edge of a cliff
Question
• Which has greater gravitational potential energy ---a book lifted
1 meter off the ground or the same book lifted 10 meters off the
ground?
• Can you prove it?
Calculations
• Wrecking ball (A) has a weight of 700N and hangs at a height of
100 meters.
• Wrecking ball (B) has a weight of 800N and hangs at a height of
80 meters.
Which has more gravitational potential energy?
Elastic Potential Energy
• An object gains a different type of potential energy when
stretched.
• The potential energy associated with objects that can be
stretched or compressed is called elastic potential energy
• Also known as stored mechanical energy.
Elastic Potential Energy
• Examples of Elastic Potential Energy:
1. Rubber bands
2. Springs
3. English long bow
Chemical Energy
• Chemical compounds are made up of
atoms and molecules
• Bonds hold atoms and molecules
together.
• THESE BONDS HAVE STORED
CHEMICAL ENERGY.
• https://www.youtube.com/watch?v=
y_omJiYB2gk
Chemical Energy
• Chemical Energy is potential energy stored in chemical bonds that
hold chemical compounds together.
• Examples of chemical Energy
1. Food
2. Fossil Fuels
3. Batteries
Nuclear Energy
• Nuclear Energy – is a type of potential energy that is stored in the
nucleus of an atom.
• Nuclear Energy is released during a nuclear reaction.
• https://www.youtube.com/watch?v=zsTRxXvQY0s
Nuclear Energy
• Examples of Nuclear Energy:
1. The sun
2. Atomic bomb
3. Nuclear Power plants
Types of Kinetic Energy
• Kinetic Energy is the energy of motion.
1.
2.
3.
4.
Electrical Energy
Electromagnetic Energy
Thermal Energy
Mechanical Energy
Electrical Energy
• The energy of electric charges is electrical energy
• Electrical Energy is caused by the movement of electrons.
Electrical Energy
• Examples of Electrical Energy:
1. Lightning
2. Electric current
3. Appliances that run on electricity
Electromagnetic Energy
• Electromagnetic Energy is energy that comes in form of the
electromagnetic spectrum.
• The electromagnetic spectrum is the range of all possible
Electromagnetic radiation.
Types of Electromagnetic Energy
• Electromagnetic Energy is also called radiant energy.
• Examples:
1.
2.
3.
4.
5.
6.
7.
Light
X-rays
Radio rays
Infrared rays
Microwaves
Gamma rays
Ultraviolet radiation
Thermal Energy
• All objects are made up of atoms and molecules and because
these particles are constantly in motion, they have kinetic energy.
Which box below has more kinetic energy? Why?
Thermal Energy
• The faster they more the more kinetic energy an object has.
• The total potential and kinetic energy of the particles of an object
are called thermal energy.
Thermal Energy
Examples:
Lava – Lava moving down the side of the hill may be moving slowly but its
particles that make up the lava are moving quickly. Because the particles
have a large amount of kinetic energy the lava has a large amount of
thermal energy.
Mechanical Energy
• The form of energy that is a associated with the position and
motion of an object is called mechanical energy.
• An objects mechanical energy is a combination of its potential
energy and kinetic energy.
Mechanical Energy = Potential Energy + Kinetic Energy
Thermal Energy and Heat
Chapter Six, Section One
Thermal Energy and Heat
Different objects at the same
temperatures CAN have different
energies.
Thermal Energy
• Remember that the total energy of all particles in an object is the
thermal energy.
• Thermal energy depends on:
1. The number of particles in the object
2. The arrangement of the object’s particles.
Thermal Energy
• The more particles an object has at a
given temperature, the more
thermal energy it has.
The containers to the right are
identical temperature, which the
least thermal energy? Why?
Heat
• Thermal energy that is transferred from matter at a higher
temperature to a lower temperature is called heat
• Only when thermal energy is transferred is it called heat
• Heat is thermal energy moving from a warmer object to a cooler
object.
Heat
Energy Transformation and Conservation
Chapter Five, Section Three
Energy Transformation
• Most forms of energy can be transformed into other forms.
• A change from one form of energy to another form of energy is
called an energy transformation.
• Types of energy transformation:
1. Single transformations
2. Multiple transformations
Single Transformations
• Sometimes one form of energy needs to be transformed into
another to get work done.
• Remember: work is force exerted on an object causing it to move
• Examples:
1. Turbines moving in the dam turning mechanical energy into electrical
energy
2. Your body converts the chemical energy in food into thermal energy that
your body uses to maintain its temperature.
What is the single transformation?
Multiple Transformation
• Often a series of energy transformations are needed to do
work(make something move).
• Examples:
1. The energy needed to strike a match is transformed first to thermal
energy. The thermal energy causes particles in the match to release the
stored chemical energy, which is transferred into thermal energy and the
electromagnetic energy you see as light
Energy Chains
• Energy cannot be created or destroyed it is never transformed just
once.
• Energy is transformed from one type to another to another and so
on.
• When we follow these transformations we get an energy chain.
Energy Chain
Transformation Between Potential and Kinetic
Energy
• The most common energy transformations is the transformation
between potential and kinetic energy.
Transformation Between Potential and Kinetic
Energy Example
Energy Transformation in Juggling:
• Any object that rises or falls experiences a change in gravitational potential
energy and kinetic energy.
1. As the ball rises it slows down-kinetic energy decreases. Since the ball is
going higher in the air, the potential energy increases.
2. At the highest point the ball stop moving for a split second, at that point
there is no kinetic energy, and its potential energy is at the highest point.
3. As the ball falls there is a loss in altitude, so the potential energy
decreases, at the same time the ball is moving faster and faster, so the
kinetic energy increases.
Energy Transformation in Juggling
Energy Transformation in a Pendulum
• Can you explain how
kinetic and potential
energy change in
the picture to the
left?
Energy Transformation in a Pole Vault
• Can you explain how
kinetic and potential
energy change in
the picture to the
left?
Conservation of Energy
• The Law of Conservation of Energy states that when one form of
energy is transformed into another, no energy is destroyed in the
process.
• According to the law of conservation of energy, energy cannot be
created nor can it be destroyed.
https://www.youtube.com/watch?v=LrRdKmjhOgw
Conservation of Energy
• This means:
1. Energy is the same before and after the
transformation
2. If you add up all the new forms of energy = the old
forms of energy
Energy and Friction
• Whenever a moving object experiences friction, some the kinetic
energy is transformed into thermal energy.
Energy and Fossil Fuels
Chapter Five, Section Four
Formation of Fossil Fuels
•
The plants of vast forests that at one time covered Earth
provide the energy stored in fuels.
• A fuel is a material that contains stored potential energy.
• Examples:
1. Gas
2. Lumber
Formation of Fossil Fuels
• Some fuels used today were made hundreds of millions of years
ago.
• These fuels, which include coal, petroleum, and natural gas are
known as fossil fuels.
Formation of Fossil Fuels
• Fossil Fuels are made of hydrocarbons
• Hydrocarbons – are chemical compounds that contain hydrogen
and carbon atoms.
• The combustion of fossil fuels provides more energy per kilogram
than does the combustion of other fuels.
Relative Amounts of Energy
• Coal
• twice the energy of wood
• Oil and natural gas
• three times the energy of wood
Coal
• Coal is a solid fuel formed from plant remains.
Coal
• Coal is the most plentiful fossil fuel in the United States.
• Advantages
• Easy to transport
• Provides a lot of energy
• Disadvantages
• Causes erosion
• Runoff causing water pollution
• Air pollution
Oil
• Oil is a thick, black, liquid fossil fuel.
Oil
• Oil forms from the remains of small animals, algae, and other
organisms that lived in oceans and shallow inland seas hundreds of
million years ago.
• Petroleum is another name for oil
Oil
• Petroleum accounts for more then 1/3 of energy produced in the
world.
• What uses petroleum:
•
•
•
•
•
Cars
Homes
Boats
Airplanes
Trains
Where is Oil Located?
• Most oil deposits are located underground in tiny holes in
sandstone or limestone.
Where is Oil Located?
• Located deep below the surface
• Finding oil is difficult
• Use sound waves to find oil
• One of every six wells drilled produces oil of useable amount
Origins of U.S. Oil
Natural Gas
• Natural Gas is a mixture of methane and other gases.
• Formed from the same organisms as oil
• Less dense than oil so it is normally found directly above it in deposits
Natural Gas
Natural Gas
• Can be compressed and made into a liquid to put in tanks for fuel.
• Advantages:
• Large amount of energy
• Low pollution
• Easy to transport
• Disadvantages
• Highly flammable
Fuel Supply and Demand
• Oil is essential to modern day life
• Since fossil fuels take hundreds of millions of years to form they
are considered nonrenewable resources.
• The oil we have today took about 500 million years to form.
• ¼ of the oil we have is already gone
• Eventually all the oil on earth will be used up.
Fuel Supply and Demand
• Many nations consume huge amounts of fossil fuels and have a
very small reserve.
• United States:
• Uses 1/3 of all oil used in the world
• Only has 3% of the world’s oil supply