Living Things

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Energy and Heat
Table of Contents What Is Energy? Forms of
Energy Energy Transformations and
Conservation Temperature, Thermal Energy, and
Heat The Transfer of Heat
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8.1 Vocabulary

• Energy
• Kinetic energy
• Potential energy
• Gravitational potential energy
• Elastic potential energy

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How are energy, work, and power related?

• Work is done when a force moves an object.
• When you do work on an object, some of your
  energy is transferred to that object.
• Energy is measured in joules, the same unit as
  work.

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• Power is the rate at which work is done.
• Since the transfer of energy is work, the power
  is the rate at which energy is transferred, or
  the amount of energy transferred in a unit of
  time.
• Power Energy Transferred / Time
• Using a machine to do work allows the same amount
  of energy in a shorter amount of time
• What is energy?

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What are two types of energy?

• The two basic types of energy are kinetic energy
  and potential energy.
• Whether energy is kinetic or potential depends on
  the motion, position, and shape of the object.

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What Is Energy?

• A moving object can do work when it strikes
  another object and moves it.

Kinetic Energy The kinetic energy of an object
depends on its speed and mass.
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Factors Affecting Kinetic Energy

• The faster an object moves, the more kinetic
  energy it has.
• Kinetic energy also increases as mass increases.

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Calculating Kinetic Energy

• Formula for KE
• KE (1/2)(Mass)(Speed)2
• So, a boy pulling a 10-kg wagon at a speed of 2
  m/s
• KE (1/2)(10kg)(2m/s)2
• Note that 1 kgm2/s2 1 joules (J)

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Do changes in the mass and speed have the same
effect? KE (1/2)(10kg)(2m/s)2 20 J

• Double the mass
• KE (1/2)(20kg)(2m/s)2

• Double the speed
• KE (1/2)(10kg)(4m/s)2

Why does this work this way?
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Potential Energy

• An object does not have to be moving to have
  energy.
• Some objects have energy as a result of their
  shapes or positions.
• You can transfer energy and the object can store
  it for future movement.
• It has the potential to do work.

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What Is Energy?
Gravitational Potential Energy The rock climbers
have gravitational potential energy, which is
potential energy related to an object's height.

• The gravitational potential energy of an object
  is equal to the work done to lift it to that
  height.

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Gravitational Potential Energy

• Since work is equal to force multiplied by
  distance, you can calculate an objects
  gravitational potential energy
• gravitational potential energy weight x height
• So if a book has a weight of 10 N and is lifted 2
  m off the ground, how much gravitational
  potential energy does it have?

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Elastic Potential Energy

• Objects that can be compressed or stretches have
  a different type of energy.
• When a rubber band is stretched or a spring is
  squeezed, it has elastic potential energy.
• The more the object is stretched or compressed,
  the more elastic potential energy it has.

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What Is Energy?
Elastic Potential Energy The energy stored in a
stretched object, such as the trampoline, is
elastic potential energy. Using 1 as the
greatest, how would you rank the amount of
elastic potential energy of the trampoline from
greatest to least?
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What Is Energy?
What is the SI unit for each quantity?
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8.2 Forms of Energy

• The form of energy associated with the motion,
  position, or shape of an object is called the
  mechanical energy.
• It is a combination of its potential energy PE
  and its kinetic energy KE.
• The higher an object moves, the greater the PE
  and the faster an object moves, the greater the
  KE. You find the total mechanical energy by
  adding its KE and PE.

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Mechanical Energy

• An object with mechanical energy can do work on
  another object, so the mechanical energy, like
  all forms of energy, is the ability to do work.
• The more mechanical energy an object has, the
  more work it can do.

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What are other forms of energy?

• An object can have other forms of KE and PE
  associated with the particles that make up the
  object.
• Forms of energy associated with the particles of
  objects include nuclear energy, thermal energy,
  electrical energy, and electromagnetic energy,
  and chemical energy.

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Nuclear Energy

• A type of potential energy called nuclear energy
  is stored in the nucleus of an atom.
• Nuclear energy is released during a nuclear
  reaction.
• Nuclear fission occurs when a nucleus splits at a
  nuclear power plant.
• Nuclear fusion occurs when the nuclei of atoms
  fuse, or join together. This occurs constantly at
  the surface of the sun, but only a small portion
  of this energy reaches the Earth.

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Forms of Energy
Nuclear Energy Use the Venn diagram to compare
and contrast nuclear fission and nuclear fusion.
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Thermal Energy

• Since particles of objects are always in constant
  motion, the object always has KE.
• If heat is applied to an object, the particles
  move faster. The faster they move, the greater
  the KE and thermal energy it has.

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Electrical Energy

• The energy of electric charges is electrical
  energy.
• Depending upon whether the charges are moving or
  stored, electrical energy can be a form of KE or
  PE.
• We rely on electrical energy from batteries or
  electrical lines to run devices.

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Electromagnetic Energy

• The light we see is one type of electromagnetic
  energy, a form of energy that travels through
  space in waves.
• The source of these waves is vibrating electrical
  charges, and they can travel through a vacuum or
  empty space.
• Other forms of electromagnetic energy are
  microwaves, x-rays, UV waves, infrared waves, and
  radio waves.

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Chemical Energy

• Chemical energy is potential energy stored in
  chemical bonds, holding atoms together.
• The food we eat, matches used to light fire, and
  the cells in our body all use chemical energy.
  These bonds are broken and release energy.

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Forms of Energy
Forms of Energy Many objects in this restaurant
have more than one form of energy. Find three
objects.
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8.3 Energy Transformations Conservation

• All forms of energy can be transformed into other
  forms of energy.
• Single transformation is changing one form of
  energy into another a toaster transforms
  electrical energy into thermal energy body
  transforms chemical energy into mechanical energy.

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Multiple Transformations

• Often, a series of energy transformations is
  needed to do work mechanical energy is used to
  strike a match, that is transformed first to
  thermal energy, then to chemical energy then to
  more thermal energy and to electromagnetic energy
  (light).

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Energy Transformations and Conservation
Multiple Transformations A series of energy
transformations must occur for you to ride your
bike. What are the forms of energy involved in
each transformation?
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Kinetic and Potential Energy

• The transformation between potential and kinetic
  energy is one of the most common energy
  transformations.
• Falling Object An object that is dropped changes
  from PE (at the highest point) to KE as it moves
  to the ground.
• Pendulum As an object swings, at the highest
  point in the swing, it looses its KE and gains
  gravitational PE. At the lowest point, the object
  has its greatest KE and no PE.

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Energy Transformations and Conservation
Pendulum A continuous transformation between
potential and kinetic energy occurs in a
pendulum. What are the types of energy the
pendulum has at positions A, B, and C?
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• Pole Vault As a person plants the pole to jump,
  the speed decreases and the pole bends created
  elastic PE. This pushes the jumper up to
  gravitational PE at his highest point. KE then
  brings him back to Earth.

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What is the Law of Conservation of Energy?

• The Law of Conservation of Energy states that
  when one form of energy is transformed to
  another, not energy is lost in the process.
• Energy cannot be created or destroyed.
• So what happens to the energy when an object
  stops moving?

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• Whenever a moving object experiences friction,
  some of its kinetic energy is transformed into
  thermal energy.
• Friction is the reason why no machine is 100
  efficient. The output is always less than the
  input because some mechanical energy is always
  transformed into thermal energy due to friction.

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Energy Transformations and Conservation
Conserving Energy While You Ride Transformations
between potential and kinetic energy occur during
a roller coaster ride. How much potential and
kinetic energy does the coaster have at each
point?
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Temperature, Thermal Energy, and Heat
Temperature Scales The chart shows a weather
report, but it does not identify the temperature
scale. Which row of temperatures do you think
represents Celsius?
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Temperature, Thermal Energy, and Heat
Thermal Energy The total amount of thermal energy
in an object depends on its temperature and how
many particles it contains. In the top two
diagrams, which chicken pot pie contains more
thermal energy? How should the bottom diagram be
completed to show three pies with more thermal
energy than the first?
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The Transfer of Heat
Where Does Heat Transfer on This Beach? Heat
transfer goes on all around you all the time,
even on the beach.
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The Transfer of Heat
Type of Heat Transfer Describe the different
types of heat transfer in the illustration.
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