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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
8.1 Vocabulary
•Energy
•Kinetic energy
•Potential energy
•Gravitational potential energy
•Elastic potential energy
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.
•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?
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.
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.
Factors Affecting Kinetic Energy
•The faster an object moves, the more
kinetic energy it has.
•Kinetic energy also increases as mass
increases.
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 kg·m2/s2 = 1 joules (J)
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?
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.
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.
Gravitational Potential Energy
•Since work is equal to force multiplied by
distance, you can calculate an object’s
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?
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.
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?
What Is Energy?
What is the SI unit for each quantity?
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.
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.
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.
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.
Forms of Energy
Nuclear Energy
Use the Venn diagram to compare and contrast nuclear fission and
nuclear fusion.
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.
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.
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.
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.
Forms of Energy
Forms of Energy
Many objects in this restaurant have more than one form of energy.
Find three objects.
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.
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).
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?
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.
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?
• 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.
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?
• 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.
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?
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?
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?
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.
The Transfer of Heat
Type of Heat Transfer
Describe the different types of heat transfer in the illustration.