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Chapter 9 Notes
Energy and Energy
Resources
Energy is the ability to do
work.
Work is a transfer of energy,
and like work, energy is
measured in Joules (J).
Forms of energy:
Kinetic energy
 is the energy of motion.
 Kinetic Energy (KE) depends
on mass (m) and speed (v).
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Kinetic Energy = mass x velocity2
2
KE = mv2
2
example#1
What is the kinetic energy of a
car that has a mass of 1200 kg
and is moving at a speed of 20
m/s ?
KE = mv2
2
KE = 1200 kg * (20 m/s)2
2
KE = 1200 kg * 400 m2/s2
2
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KE = 480,000 kg*m2/s2
2
KE = 240,000 kg m2/s2
or
240,000 J
Practice problems:
#2 What is the kinetic energy
of a car that has a mass of
2400 kg and is moving at 20
m/s?
KE = mv2
2
KE = 2400 kg * (20 m/s)2
2
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KE = 2400 kg * 400 m2/s2
2
KE = 960,000 kg*m2/s2
2
KE = 480,000 kg m2/s2
or
480 000 J
How does the kinetic
energy compare to the
example problem above?
#3 What is the kinetic energy
of a car that has a mass of
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1200 kg and is moving at a
speed of 40 m/s ?
KE = mv2
2
KE = 1200 kg * (40 m/s)2
2
KE = 1200 kg * 1600 m2/s2
2
KE = 1,920,000 kg*m2/s2
2
2
KE = 960,000 kg m /s
2
or
960,000 J
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What is the kinetic energy of a
4,000 kg elephant that is
running at 2 m/s?
At 4 m/s?
How do the two kinetic
energies compare to one
another? QUADRUPLES !
#3 What is the kinetic energy
of a 2,000 kg bus that is
moving at 30 m/s?
Potential energy
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 is energy of position or
condition.
 It is stored energy held in
readiness to do work.
 Gravitational, chemical, and
Elastic potential energy
Elastic PE is when an object is
stretched or compressed.
examples rubber band,
ball, spring
Gravitational potential
energy depends on the
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height of an object. It is
measured in Joules.
GPE = weight * height
example:
A book is placed on a shelf 2.5
meters off the floor. It has a
weight of 0.65 N, what is the
potential energy?
GPE = weight * height
GPE = 0.65 N * 2.5 m
GPE = 1.625 N * m
(or 1.625 J)
**If you don’t know weight,
but know mass of object use:
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GPE = mass * acceleration * height
of gravity
GPE = M * 9.8 m/s2 * H
example: A glass with a mass
of 0.5 kg is on the edge of a
table 1 m off the floor. What is
the potential energy?
GPE = M * 9.8 m/s2 * H
2
GPE = .5 kg * 9.8 m/s * 1m
GPE = 4.9 kg* m/s2 *m
GPE = 4.9 N*m
(or 4.9 J)
 Other forms of energy:
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 Mechanical Energy is the
total energy of motion and
position of an object. It
could be pushing, pulling, or
throwing.
examples: moving bike,
running, jumping frog, sound
 thermal (energy of
particles)
 chemical energy is stored
in chemical bonds of the
foods we eat, in a match,
batteries, fossil fuels (coal,
petroleum, natural gas)
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 electrical energy is energy
from moving electrons
 electromagnetic energy is
radiant or light energy.
visible light, microwaves,
ultraviolet and infrared
radiation, x-rays, radio
waves
 nuclear energy is stored in
the nucleus of an atom.
Released when nucleus splits
(fission) like in reactors,
or when nuclei join (fusion)
like in stars.
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The Law of Conservation of
Energy
When one form of energy is
converted to another, no
energy is destroyed in the
process.
**Energy can be transformed
from one type to another.
***In any conversion, some of
the energy is lost to the
environment as heat.
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