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Chapter 15
Page 446-467
Chapter 15 Section 1
Pg. 446-452
Energy and Work
• Work- done when a force moves an object
through a distance, a transfer of energy
– Measured in joules (J)
• Energy- the ability to do work
– It is known by the changes it causes
– Examples are sound and motion
– Measured in joules (J)
• 1 joule = 1 newton-meter
• When work is done on an object, energy is
transferred to that object
Kinetic Energy
• Kinetic Energy- the energy of motion
– Comes from the Greek work kinetos, meaning
“moving”
– The kinetic energy of any moving object depends
upon its mass and speed.
Math Practice
• Page 448
Potential Energy
• Potential Energy- energy that is stored as a
result of position or shape
– Stored energy gets converted into kinetic energy
– You can store energy just by picking up a book and
holding it. Let go, and that stored energy will turn
into the kinetic energy of motion
Gravitational Potential Energy
• Gravitational Potential Energy- potential
energy that depends upon an object’s height
– The PE increases when an object is raised to a
higher level
– Depends on an object’s mass, height, and
acceleration due to gravity (9.8 m/s2)
Elastic Potential Energy
• Elastic Potential Energy- PE of an object that
is stretched or compressed
– Said to be elastic if it springs back to its original
shape after it is stretched or compressed
– Can also be stored in objects that are compressed,
such as springs
– Broken rubber band: it’s elastic PE is converted
into kinetic energy
Forms of Energy
• All energy can be considered to be
kinetic energy, potential energy, or
the energy in fields such as those
produced by electromagnetic waves
– Ex: fireworks, nuclear energy, lightning bolts, etc.
• The major forms of energy are mechanical
energy, thermal energy, chemical energy,
electrical energy, electromagnetic energy,
and nuclear energy
Mechanical Energy
• Mechanical Energy- the energy associated with
the motion and position of everyday objects
– Not limited to machines
– The sum of an object’s potential energy and kinetic
energy
Mechanical Energy = KE + PE
– Ex: speeding trains, bouncing balls, sprinting athletes
• Does NOT include thermal, chemical or other energy
associated with the motion or arrangement of atoms or
molecules
Thermal Energy
• Thermal Energy- the total potential and
kinetic energy of all the microscopic particles
in an object
• When an object’s atoms move faster, its
thermal energy increases and the object
becomes warmer
Chemical Energy
• Chemical Energy- the energy stored in
chemical bonds
– When bonds are broken, the released energy can
do work
– Example: wood burning, when gasoline is burned
Electrical Energy
• Electrical Energy- the energy associated with
electric charges
– Electric charges can exert forces that do work
– Example: batteries
Electromagnetic Energy
• Electromagnetic Energy- a form of energy that
travels through space in the form of waves
– Radiated by the sun
– Examples: visible light, X-rays
Nuclear Energy
• Nuclear Energy- the energy stored in atomic
nuclei
– Examples: nuclear fission (is a process that
releases energy by splitting nuclei apart) and
nuclear fusion (releases energy when less massive
nuclei combine to form a more massive nucleus)
Chapter 15 Section 2
Page 453-459
Energy Conversion
• Energy can be converted from one form to
another, known as energy conversion
• Examples:
– Wind-up toys: store elastic PE in spring, when
released the PE is converted to KE and the toy
moves
– Light bulbs: convert electrical energy to thermal
and electromagnetic energy
– See more on page 454 of book
Conservation of Energy
• The law of conservation of energy states that
energy cannot be created or destroyed
– Energy can be converted from one form to
another
– In a closed system, the amount of energy present
at the beginning of a process is the same as the
amount of energy at the end
– See example on page 455
Energy Conversions
• Gravitational potential energy of an object is
converted to the kinetic energy of motion as
the object falls
• Conversions between KE and PE can happen in
both directions
Energy Conversion in Pendulums
• Rope swing is an example of a pendulum.
– Pendulum consists of a weight swinging back and
forth from a rope or string
– KE and PE undergo constant conversion as a
pendulum swings.
– At HIGHEST point in swing, pendulum is
momentarily motionless: the weight at the end
has zero KE and maximum PE
– As is swings downward, PE is converted to KE
– At the bottom of the swing, the pendulum has
maximum KE and zero PE
Energy Conversion in the Pole Vault
• Pole-vaulter’s KE is partially converted into
elastic PE as the pole bends. It springs back
into shape, propelling the pole-vaulter upward
– As he soars KE decreases while he gains
gravitational PE
– At the highest point, gravitational PE begins to
convert back to KE
Energy Conversion Calculations
• Conservation of Mechanical Energy
– When friction is small enough to be ignored
• Math Practice pg. 458
Energy and Mass
• Einstein (1879-1955)
– Developed theory of relativity
• E = mc2
(Energy = mass X c-the speed of light squared)
• Einstein’s equation, E =mc2 says that energy
and mass are equivalent and can be
converted into each other
– In other words: energy is released as matter is
destroyed, and matter can be created from
energy
Energy and Mass
• In nuclear fission and fusion reactions, large
amounts of energy are released by the
destruction of very small amounts of matter.
• The law of conservation of energy has been
modified to say that mass and energy
together are always conserved
Chapter 15 Section 3
Page 462-466
Nonrenewable Energy Resources
• Nonrenewable energy resources- exist in
limited quantities, once used, cannot be
replaced except over the course of millions of
years
• Examples: oil, natural gas, coal, and uranium
• Fossil fuels: oil, natural gas, and coal
– Creates pollution
• Many of these resources are being used faster
than they can be replaced
Nonrenewable Energy Resources
Renewable Energy Resources
• Renewable energy resources- resources that
can be replaced in a relatively short period of
time
– Most originate directly/indirectly from the sun
– Example: hydroelectric, solar, geothermal, wind,
biomass
– Challenge is to find efficient ways to make these
energy resources inexpensive and convenient
Renewable Energy Resources
Hydroelectric Energy
• Hydroelectric energy- energy obtained from
flowing water
• As water flows downhill, its gravitational PE is
converted into KE which can be used to turn
turbines that are connected to electric
generators
• Many hydroelectric power plants rely on dams
– Cause a few environmental problems (fish
spawning)
Hydroelectric Energy
Solar Energy
• Solar energy- sunlight that is converted into
usable energy
– nonpolluting
Geothermal Energy
• Geothermal energythermal energy beneath
Earth’s surface
• Steam is used to drive
electric generators
• Nonpolluting
• Not widely available
Other Renewable Resources
• Biomass energy- the chemical energy stored
in living things
– Can be converted directly into thermal energy (ex:
wood burning)
• Hydrogen fuel cell- generates electricity by
reacting hydrogen with oxygen
– End product is water, nonpolluting
Renewable vs. Nonrenewable
Conserving Energy Resources
• Energy resources can be conserved by
reducing energy needs and by increasing the
efficiency of energy use
• Energy conservation- finding ways to use less
energy or to use energy more efficiently
– Turn of lights when not in use
– Energy efficient products (appliances, cars, light
bulbs)