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Chapter 15
Sections 1-2
Energy is the ability to do work.
 Energy is measured in Joules, just like
work.
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The energy of motion is called kinetic energy.
To calculate the kinetic energy of an object,
multiply half the object’s mass (m) by its speed
(v) squared. FORMULA: KE = ½ mv2
Potential energy is energy that is stored as a
result of position or shape.
The potential energy of an object that is
stretched or compressed is known as elastic
potential energy.
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Potential energy that depends on an
object’s height is called gravitational
potential energy.
Gravitational potential energy is calculated
by multiplying the object’s mass (m) by the
acceleration due to gravity (g) and its height
above the ground (h).
FORMULA: GPE = mgh
g = 9.8 m/s/s
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Find the kinetic energy of a 0.1kg toy truck
moving at a speed of 1.1 m/s.
KE = ½ mv2
KE = ½ (0.1kg)(1.1m/s)2
KE = 0.0605 Joules
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A book on a shelf 2m above the floor has a
mass of 1.5kg. What is the gravitational
potential energy of the book?
GPE = mgh
GPE = (1.5kg)(9.8m/s/s)(2m)
GPE = 29.4 Joules
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Which runner has the greater kinetic energy: a
46kg runner moving at a speed of 8 m/s or a 92kg
runner moving at a speed of 4 m/s?
Runner 1
KE = ½ mv2
KE = ½ (46kg)(8m/s)2
KE= 1472 Joules
Runner 2
KE = ½ mv2
KE = ½ (92kg)(4m/s)2
KE = 736 Joules
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If a 6kg box is moved from the floor to a
storage compartment 2m above the floor, by
how many joules does its potential energy
change?
GPE = mgh
GPE = (6kg)(9.8m/s/s)(2m)
GPE = 117.6 Joules
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The total energy of motion (KE) and position (PE) of
any object is its mechanical energy (ME).
FORMULA: ME = PE + KE
Sound energy is a form of mechanical energy. It
involves the compression and expansion of air
particles, thus has both kinetic and elastic
potential energy.
The total potential and kinetic energy of all the
microscopic particles in an object make up its
thermal energy. This is also known as heat energy.
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Chemical energy is the energy stored in chemical
bonds.
Electrical energy is the energy associated with
electrical charges.
Electromagnetic energy is a form of energy that
travels through space in the form of waves. This
includes light energy, x-rays, microwaves, and
other forms of electromagnetic waves.
Nuclear energy is energy stored in the nuclei of
atoms (fission, fusion).
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The process of changing energy from one
form to another is energy conversion.
Every energy conversion involves some
conversion to thermal energy due to
friction.
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When energy changes from one form to another,
the total amount of energy stays the same.
The gravitational potential energy of an object is
converted to the kinetic energy of motion as an
object falls.