Transcript Chapter 7

Chapter 7
Potential Energy and
Energy Conservation
PowerPoint® Lectures for
University Physics, Twelfth Edition
– Hugh D. Young and Roger A. Freedman
Lectures by James Pazun
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Gravitational potential energy
• The path of the
basketball can
demonstrate many
principles of
potential and kinetic
energy.
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Athletes and the conservation of energy
• Refer to Figure 7.3.
• Notice how potential and kinetic energy interchange as the
athlete jumps.
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Athletes and energy II—Example 7.1
• Refer to Figure 7.4 as you follow Example 7.1.
• Notice how velocity changes as forms of energy
interchange.
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Forces other than gravity doing work
• Refer to
Problem-Solving
Strategy 7.1.
• Follow the
solution of
Example 7.2.
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Work and energy along a curved path
• Notice the same
expression for
gravitational
potential energy is
the same along
either a curved or
straight path.
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Consider projectile motion using energetics
• Consider the speed
of a projectile as it
traverses its
parabola in the
absence of air
resistance.
• Refer to
Conceptual
Example 7.3 and
Figure 7.8.
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What’s the speed in a vertical circle?
• Refer to Example 7.4 and Figure 7.9.
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Speed in a vertical circle with friction
• Consider how
things change
when friction is
introduced.
• Refer to
Example 7.5
and Figure 7.10.
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The energy of a crate on an inclined plane
• Refer to Example
7.6 and Figure
7.11.
• The force of
friction does
negative work
decreasing the
total mechanical
energy.
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Work and energy in the motion of a mass on a spring
• Notice the work done as the spring expands and
contracts at right in Figure 7.13.
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Work and energy in the motion of a mass on a spring II
• See the parabolic potential energy curve in Figure
7.14 below.
• Problem-Solving
Strategy 7.2
requires that we
follow gravitational
potential energy,
kinetic energy, and
elastic band
potential energy.
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Motion with elastic potential energy—Example 7.7
• Example
7.8 also
examines
elastic
potential
energy.
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Bring together two potential energies and friction
• Example 7.9
considers the
emergency stop
system on an
elevator.
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Conservative forces
• The work by a conservative force like gravity does
not depend on the path your hiking team chooses,
only how high you climb.
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Friction does depend on the path taken
• Consider Example 7.10
where the nonconservative
frictional force changes with
path.
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Energy diagrams give us insight
• Figure 7.23 shows the
situation and the
resulting energy
diagram. Information
may be discerned
about limits and zeros
for the physical
properties involved.
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The potential energy curve for motion of a particle
•
Refer the potential energy function and its corresponding components of force.
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