Energy
= the ability to do work.
Energy
• The energy released by
a supernova is capable
of destroying a nearby
solar system in just a
few hours. A supernova
is one of the greatest
concentrations of
energy in the universe.
Nature of Energy
Energy is all around you.
• You hear energy as sound, you see
energy as light, you can feel energy in
wind.
• Living organisms need energy for
growth and movement.
• You use energy when you hit a tennis
ball, compress a spring, or lift a
grocery bag.
Because energy is the
ability to do work, it is
measured in Joules.
Units of Energy
= Joules (J)
What is Energy?
Energy
THE ABILITY TO CHANGE OR MOVE MATTER
 The ability to produce change in itself or the
environment
THE ABILITY TO DO WORK
Other ways to explain it:
 “The ability of a system to produce change in itself or
the environment”
 “The capacity or actuality of change in a system”
 When energy is released or absorbed something
changes in the system. (and surroundings!)
 When energy is stored in a system, the capacity for
spontaneous change is inherent.
 Potential Energy
 Stored energy
 Kinetic Energy
 Energy of motion
 Mechanical Energy
 Total Energy of a System (PE + KE)
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2 Types of Energy:
Kinetic Energy (KE)
(Energy of Movement)
and
Potential Energy (PE)
(Stored Energy)
Elastic
Potential Energy
= Energy
stored in a
stretched or
compressed
material
(spring,
rubber band,
bungee cord,
bow, etc.)
We will concentrate on
Gravitational Potential Energy
gravitational PE = Weight x Height
Remember, Weight is defined as
W = mg
So, gravitational PE can be written as (mg) x h
PE = mgh
Gravitational
Potential Energy
= Energy stored
due to height
from the
ground
(depends on
weight and
height)
Kinetic Energy (KE)
• The energy of motion.
• The faster the object
moves – the more kinetic
energy.
• The motion of molecules is
what causes HEAT, so:
HEAT is a form of kinetic energy.
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Kinetic Energy
Formulas:
Kinetic Energy:
KE = ½ mv2
KE = ½ mv2
KE depends on
mass and velocity.
•KE = ½(mass x
v=
velocity2)
kg m2/s2 =Newton*meter=
Joules
Potential Energy:
m=

PE = mgh
2KE
Weight = mg
(g = 9.8 m/s2)
m
2KE
PE
v2
m g h
PE Sample Problem:
PE Sample Problem:
This person, who
weighs 725
Newtons, is
currently 20.0
meters above the
ground. What is
their gravitational
PE ?
KE Sample Problem:
This 8,200kg
roller coaster
is moving at
7.6 m/s.
What is the
kinetic energy
of the
coaster ?
This coaster must
have a PE of no
more than 824,000
Joules to survive
this 12.0 meter
drop. What is the
greatest mass the
coaster can have?
KE Sample Problem:
This roller coaster has a total of
604,800 J of kinetic energy when it
is travelling at its fastest, 12 m/s .
What is the mass of the coaster?
3
KE Sample Problem:
This 45,000kg
roller coaster has
a total of
840,000 J of
kinetic energy.
What is the
velocity of the
coaster ?
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Mechanical Energy
Conservation of Energy
= the total energy of a system
Energy cannot be created or destroyed.
KE + PE = ME
•Energy MAY be
converted from one
form to another…
…but the total
mechanical energy
of a system remains
the same.
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Energy MAY be converted from one form to another.
Energy Transformation for a Dart
Here, gravitational potential energy is converted
to kinetic energy, but energy is conserved;
the total mechanical energy (TME) remains unchanged.
Energy Transformation on a Roller Coaster
v=0
KE = 0
PE = max
PE = ME
ME = PE h=max = KE h=0
h=0
PE = 0
KE = max
KE = ME
KE + PE = ME
How High Will It Go?
Energy Transformation for a Pendulum
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Forms of Energy
Energy Transformation for a Dart
• There are many types of
kinetic and potential
energy:
• Heat (KE)
• Chemical (PE)
• Electromagnetic (PE/KE)
• Nuclear (KE/PE)
The skiier begins at an elevated position, thus possessing
a large quantity of potential energy (i.e., energy of vertical
position
Heat Energy
• Remember, heat is a form of kinetic energy…
…the faster the molecules move, the more
heat energy is produced.
This energy state is maintained until the skiier meets a
section of unpacked snow and skids to a stop under
the force of friction
Chemical Energy
• Energy that exists in the bonds
that hold atoms together.
• When bonds are broken,
chemical energy is released.
Examples:
• Digesting food…bonds are
formed to release energy for
your body to store and use.
• Sports… your body uses energy
stored in your muscles obtained
from food.
• Fire–a chemical change.
Often, the usable energy of a system will
be “lost to friction”; the energy is still
there, but it has been converted into heat.
Nuclear Energy
• When the nucleus of an atom splits, nuclear
energy is released.
• Nuclear energy is the most concentrated
form of energy.
• Fission/fusion
Sodium metal reacts with water.
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Electromagnetic Energy
Moving electric charges.
Examples:
• Power lines carry
electricity
• Electric motors are driven
by electromagnetic energy
• Light is this form of
energy (X-rays, radio
waves, laser light etc.)
A
1.
2.
3.
4.
B
What is the velocity of the coaster when it is at point A?
What is the KE of the coaster when it is at point A?
What is the height of the coaster when it is at point B?
What is the PE of the coaster when it is at point B?
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