Download Chapter 15 Energy

10/11/2016
The Nature of Energy
4.1
Pearson Prentice Hall
Physical Science: Concepts in Action
What is energy? - Bellringer
• What is Energy?
Chapter 15
Energy
15.1 Energy and Its Forms
• Objectives:
• 1. Describe and compare how energy
and work are related
• 2. Explain what factors kinetic energy
of an object depends on
• 3. Discuss how gravitational potential
energy is determined
• 4. Summarize the major forms of
energy
How Energy & Work are Related + Kinetic
Energy
• Def: energy is the ability to do work or cause change
• Work is a transfer of energy
The Nature of Energy
4.1
Different Forms of Energy
• Energy has several different forms
• Examples?
Kinetic Energy
Potential Energy
• Work with your elbow partner and
discuss any forms of energy you can
think of and an example.
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What is Mechanical Energy?
o Energy due to a
object’s motion (kinetic)
or position (potential).
Radiant
Electrical
Chemical
Mechanical
Thermal
Sound
Magnetic
Nuclear
The bowling ball has
mechanical energy.
When the ball strikes
the pins, mechanical
energy is transferred to
the pins!
Potential energy + Kinetic energy = Mechanical energy
Mechanical energy is the
movement of machine parts.
Mechanical energy is also the
total amount of kinetic and
potential energy in a system.
Wind-up toys, grandfather
clocks, and pogo sticks are
examples of mechanical energy.
Wind power uses mechanical
energy to help create
electricity.
Example of energy
changes in a swing
or pendulum.
Potential energy + Kinetic energy =
Mechanical energy
Examples of Mechanical Energy
Radiant energy is also called electromagnetic energy.
Radiant energy is the movement of photons. All life on earth
is dependent on radiant energy from the sun. Examples of
radiant energy include radio waves (AM, FM, TV),
microwaves, X-rays, and plant growth. Active solar energy
uses photovoltaic panels and light to turn radiant energy into
chemical energy.
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What is Electrical Energy?
Electrical energy is the
movement of elections.
Lightning and static
electricity are examples of
electrical energy that occur
naturally. Science hasn't
found a way to use natural
forms of electrical energy,
like lightning. Instead, we
use different energy sources
to create electrical energy
by using generators and
turbines.
o Energy caused by
the movement of
electrons
o Easily transported
through power lines
and converted into
other forms of energy
What is Chemical Energy?
o Energy that is
available for release
from chemical
reactions.
The chemical bonds in
a matchstick store
energy that is
transformed into
thermal energy when
the match is struck.
Examples of Chemical Energy
Chemical energy is the energy
stored in the bonds of atoms
and molecules. This a form of
potential energy until the bonds
are broken. Fossil fuels and
biomass store chemical energy.
Products that contain chemical
energy include: TNT, baking
soda, and a match. Biomass,
petroleum, natural gas, propane
and coal are examples of stored
chemical energy.
The Nature of Energy
4.1
Bellringer
• What is one of the forms of energy covered
yesterday, and explain how it works?
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What is Thermal Energy?
Nuclear energy is the energy
stored in the nucleus of an
atom. Nuclear energy is
unusual in that it can give
off energy in the form of
light or heat, but it is the
change in the atom's makeup
that produces the energy.
Submarines, power plants,
and smoke detectors all use
nuclear energy. Nuclear
power plants use uranium, a
radioactive element, to
create electricity.
Thermal energy is the internal
energy in substances-the
vibration and movement of atoms
and molecules within substance.
Thermal energy is created in the
movement of atoms. Boiling
water, burning wood, and rubbing
your hands together really fast
are all examples of heat energy.
Geothermal and passive solar are
sources of heat energy, but
biomass (a type of chemical
energy) can be burned to produce
heat energy.
o Heat
energy
o The heat energy of an
object determines how
active its atoms are.
A hot object is one whose atoms
and molecules are excited and
show rapid movement.
A cooler object's molecules and
atoms will show less movement.
Sound energy is the
movement molecules in the
air that produces vibrations.
Alarms, music, speech,
ultrasound medical
equipment all use sound
energy. VCR tapes change
sound energy into electrical
energy. The electrical energy
records the sound using
magnetic tape. Speakers read
the magnetic tape and change
it back into sound.
Forms of Energy
Magnetic energy is the
attraction of objects
made of iron. Medical
equipment, compass,
refrigerator magnets are
all examples of magnetic
energy. Any type of
energy source that uses a
generator in the process
to make electricity uses
magnetic energy.
• The major forms of energy are mechanical
energy, thermal energy, chemical energy,
electrical energy, electromagnetic energy
and nuclear energy
• Def: mechanical energy is the energy
associated with the motion and position
of everyday objects
• Def: thermal energy is the total PE and KE
of all the microscopic particles in an object
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• Def: chemical energy is the energy
stored in chemical bonds
• Def: electrical energy is the energy
associated with electric charges
• Def: Radiant or electromagnetic energy
is a form of energy that travels through
space in the form of waves
• Def: nuclear energy is the energy
stored in atomic nuclei
QUIZ TIME!
Electrical energy is
transported to your house
through power lines.
When you plug an electric fan
to a power outlet, electrical
energy is transform into what
type of energy?
MECHANICAL ENERGY
QUIZ TIME!
What type of energy
cooks food in a
microwave oven?
ELECTROMAGNETIC
ENERGY
What type of energy is
the spinning plate inside
of a microwave oven?
MECHANICAL ENERGY
QUIZ TIME!
What energy transformation
occurs when an electric lamp is
turned on?
ELECTRICAL ENERGY

ELECTROMAGNETIC ENERGY
What types of energy are shown below?
What type of energy is shown below?
Mechanical and Thermal Energy
(Don’t forget friction)
Chemical Energy
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What types of energy are shown below?
What type of energy is shown below?
Electrical, Mechanical and
Electromagnetic Energy
Chemical Energy (yummy)
What type of energy is shown below?
How Energy & Work are Related + Kinetic
Energy
• Def: energy is the ability to do work or cause change
• Work is a transfer of energy
Thermal Energy
Work is the transfer of energy through
motion. In order for work to take place, a
force must be exerted through a distance.
The amount of work done depends on two
things: the amount of force exerted and the
distance over which the force is applied.
There are two factors to keep in mind when
deciding when work is being done:
something has to move and the motion must
be in the direction of the applied force.
Work can be calculated by using the
following formula: Work=force x distance
Si unit for Work is the same as in Energy – Joules
Force is measured in Newtons
Distance is measured in meters
1 J = 1N x 1m
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Work is done on the books
when they are being lifted,
but no work is done on
them when they are being
held or carried
horizontally.
Practice Problems
• Calculate the KE of a 1500kg car moving
at 29m/s.
• A bowling ball traveling at 2.0m/s has 16J
of KE. What is the mass of the bowling
ball in kg?
Practice Problems
• Calculate the PE of a car with a mass of
1200kg at the top of a 42m hill.
How Energy & Work are Related + Kinetic
Energy
• The formula is: KE = ½ mv2 where m = mass and v is
the velocity (which must be squared)
• the units for m are kg & v = (m/s)2 or m2/s2
• the units for PE are kg*m2/s2 which is also called
joules, J
• Calculate the PE of a 55g egg held out of
a 2nd story window, 6m off the ground.
The Nature of Energy
4.1
The Nature of Energy
4.1
Kinetic Energy
• Kinetic energy is the energy a moving object
has because of its motion.
• The kinetic energy of a moving object
depends on the object’s mass and its speed.
Kinetic Energy
• The SI unit of energy is the joule,
abbreviated J.
• If you dropped a softball from a height of
about 0.5m, it would have a kinetic energy of
about one joule before it hit the floor.
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The Nature of Energy
4.1
Potential Energy
The greater the mass or velocity of a moving object, the
more kinetic energy it has.
• Even motionless
objects can have
energy. This
energy is stored
in the object.
• A hanging apple
in a tree has
stored energy.
The Nature of Energy
Potential Energy
4.1
Potential Energy
• Energy of
Postition.
• Stored energy
• Gravitational
potential energy
(GPE) is energy
stored by objects
due to their
position above
Earth’s surface.
• An object’s gravitational PE depends on its
mass, height & acceleration due to gravity
• The formula for gravitational PE = mgh where
m= mass (kg), g= 9.8 m/s2 (the free fall
acceleration of gravity) & h = height in meters,
m
• When you multiply all the units together you
get kg*9.8m/s2*m or kg*m2/s2 which is J
• Def: elastic PE is the PE of an object that is
stretched or compressed
• An object is elastic if it springs back after being
stretched
• Def: potential energy is stored energy as a
result of position or shape
• PE is energy with the potential to do work
• Two forms of PE are gravitational PE and
elastic PE
• Def: gravitational PE is PE that depends
upon an object’s height
• Gravitational PE increases when an object is
at a higher height
The Nature of Energy
4.1
Gravitational Potential Energy
• On Earth the acceleration of gravity is
9.8 m/s2, and has the symbol g.
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The Nature of Energy
4.1
Elastic Potential Energy
Elastic Potential Energy
• Elastic potential energy- energy stored
by something that can stretch or
compress.
The Nature of Energy
4.1
Chemical Potential Energy
• chemical potential energy- Energy
stored in chemical bonds is.
15.2 Energy Conversion &
Conservation
• Objectives:
• 1. Describe how energy can be converted
from one form to another
• 2. Explain the law of conservation of
energy
• 3. Discuss the energy conversion that
takes place as an object falls toward
Earth
• 4. Discuss how energy and mass are
related
Energy Can be Converted from One
Form to Another
• Def: energy conversion is the process of changing
energy from one form to another
• Sometimes energy is converted to other forms in
a series of steps
• Ex: striking a match uses chemical energy from
your muscles, then friction between match and
box converts KE to thermal energy, thermal
energy triggers a chemical reaction releasing
more chemical energy
• Often energy converts directly from one form to
another
• a wind up toy, for example, is PE to KE
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Conservation of Energy
4.2
Conservation of Energy
4.2
Transforming Electrical Energy
• Lightbulbs transform electrical energy into
light so you can see.
• The warmth you feel around the bulb is
evidence that
some of that
electrical
energy is
transformed
into thermal
energy.
Transforming Chemical Energy
• In a car, a spark plug
fires, initiating the
conversion of chemical
potential energy into
thermal energy.
Conservation of Energy
4.2
Conservation of Energy
4.2
Transforming Chemical Energy
• As the hot gases expand,
thermal energy is
converted into kinetic
energy.
Transforming Chemical Energy
• Some energy transformations are less
obvious because they do not result in
visible motion, sound,
heat, or light.
• Every green plant
you see converts
light energy from the
Sun into energy
stored in chemical
bonds in the plant.
Conservation of Energy
4.2
Conservation of Energy
4.2
Conversions Between Kinetic
and Potential Energy
• Mechanical energy
mechanical energy = potential energy + kinetic energy
Falling Objects
• An apple on a tree has gravitational
potential energy due
to Earth pulling
down on it.
• The instant the apple
comes loose from the
tree, it accelerates
due to gravity.
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Conservation of Energy
4.2
Conservation of Energy
4.2
Falling Objects
• As objects fall, they lose height and
gravitational potential
energy.
• Potential energy is
transformed into
kinetic energy as the
velocity increases.
Falling Objects
• If the potential energy is being converted
into kinetic energy, then the mechanical
energy of the apple doesn’t change as it
falls.
• The potential energy that the apple loses
is gained back as kinetic energy.
• The form of energy changes, but the total
amount of energy remains the same.
Conservation of Energy
4.2
Conservation of Energy
4.2
Energy Transformations in
Projectile Motion
• Energy transformations also occur
during projectile motion when an object
moves in a curved path.
Energy Transformations in
Projectile Motion
• However, the mechanical energy of the ball
remains constant as it rises and falls.
Conservation of Energy
4.2
Energy Transformations in
a Swing
• When you ride on a swing part of the fun is
the feeling of almost falling as you drop
from the highest
point to the lowest
point of the swing’s
path.
Conservation of Energy + Energy
Conversions and Gravity
• The Law of Conservation of Energy states that
energy cannot be created or destroyed
• The gravitational PE of an object is converted to
the KE of motion as an object falls
• Pendulums constantly convert PE to KE and KE to
PE as the pendulum swings
• At the bottom of the swing, the pendulum has
maximum KE and zero PE
• On either side the pendulum will have a
combination of PE + KE
• Q: Where is the PE the greatest and KE zero?
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Conservation of Energy
Energy and Mass
4.2
The Law of Conservation
of Energy
• Energy can change from one form to
another, but the total amount of energy
never changes.
•
•
•
•
Mechanical energy = KE + PE
Mechanical energy is also conserved
(KE + PE)beginning = (KE + PE) end
Einstein has an equation: E = mc2 where E is energy
(J), m is mass (kg) & c2 is the speed of light squared
(3 x 108 m/s)2
• This equation says that energy and mass are
equivalent and can be converted into each other
• It also means that a tiny amount of matter can
produce enormous amounts of energy
• Mass and energy together are always conserved
Conservation of Energy
4.2
Conservation of Energy
4.2
The Effect of Friction
• You know from
experience that if
you don’t continue
to pump a swing
or be pushed by
somebody else,
your arcs will
become lower and
you eventually
will stop swinging.
The Effect of Friction
• The mechanical (kinetic and potential)
energy of the swing seems to decrease, as if
the energy were being destroyed.
• Is this a violation of the law of conservation
of energy?
Conservation of Energy
4.2
Conservation of Energy
4.2
The Effect of Friction
• With every movement, the swing’s ropes or
chains rub on their hooks and air pushes on
the rider.
• Friction causes
energy to change to
thermal energy.
The Effect of Friction
• With every pass of the swing, the
temperature of the hooks and the air
increases a little, so the mechanical
energy of the swing is not destroyed.
• Rather, it is transformed into thermal energy.
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15.3 Energy Resources
Nonrenewable and Renewable
• Objectives:
• 1. Give examples of the major
nonrenewable and renewable
energy sources
• 2. Explain how energy
resources can be conserved
• Nonrenewable energy resources
include oil, natural gas, coal and
uranium
• Oil, natural gas and coal are fossil fuels
• Fossil fuels were formed underground
from once living organisms
• Most nonrenewable resources are
considered inexpensive, available and
are known to cause pollution
• Renewable energy resources include
hydroelectric, solar, geothermal, wind, and
biomass
• Def: hydroelectric energy is energy obtained from
flowing water
• Hydroelectric energy production usually involves
the building of a dam
• Hydroelectric is available, used today and
generally nonpolluting
• Def: solar energy is sunlight converted to usable
energy
• Solar energy is expensive and its use is limited
until technology improves
• Def: geothermal energy is thermal energy
beneath the earth’s surface
• It is nonpolluting and available in this area due to
naturally occurring hot springs
• most places are not near a volcano or hot springs
• Def: biomass energy is the energy stored in living
things
• Biomass can be converted directly to thermal
energy
• Agricultural waste such as turning corn into
ethanol for auto fuel is an example
• This technology is moderately expensive
• Wind energy requires a lot of land and a
place that has a lot of wind
• It is expensive and not practical at this time
although research continues
• Hydrogen fuel cells are being used in some
places to generate electricity by reacting
hydrogen with oxygen
• The main source of hydrogen is water
• This technology is expensive and considered
to be a research and development project
for future energy sources
Conservation of Resources
• Energy resources can be conserved by
reducing energy needs and by
increasing the efficiency of energy use
• Def: energy conservation is finding
ways to use less energy or use energy
more efficiently
• Q: Can you think of some ways we can
conserve energy resources?
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