Raymond A. Serway
John W. Jewett
Chapter 7
Conservation of Energy

7.1 Analysis Model: Nonisolated
System (Energy)
•
In a nonisolated system:
•
Energy crosses boundary of the system due to
interaction with the environment
•
For example, the work-kinetic energy
theorem:
•
Interaction of system with environment is work
done by external force
•
Quantity in system that changes is kinetic energy

7.1 Analysis Model: Nonisolated
System (Energy)
Methods of energy transfer:
•
Work
: transfers energy by applying a force
and causing a displacement of the point of
application of the force
•
Mechanical Waves
: allow a disturbance to
propagate through a medium
•
Heat
: is driven by a temperature difference
between two regions in space

7.1 Analysis Model: Nonisolated
System (Energy)
•
Matter Transfer
: matter physically crosses
the boundary of the system, carrying energy
with it
•
Electrical Transmission
: transfer is by
electric current
•
Electromagnetic Radiation
: energy is
transferred by electromagnetic waves

7.1 Analysis Model: Nonisolated
System (Energy)

7.1 Analysis Model: Nonisolated
System (Energy)
•
Energy is conserved
•
This means that energy cannot be created or
destroyed
•
If the total amount of energy in a system
changes, it can only be due to the fact that
energy has crossed the boundary of the system
by some method of energy transfer

7.1 Analysis Model: Nonisolated
System (Energy)
•
Mathematically,
E
system
=
•
E
system
is the total energy of the system
•
T
is the energy transferred across the system
boundary
•
Note:
T
work
=
W
and
T
heat
=
Q
•
Others do not have standard symbols, so we use:
•
T
MW
(mechanical waves)
•
T
MT
(matter transfer)
•
T
ET
(electrical transmission)
•
T
ER
(electromagnetic radiation)

7.1 Analysis Model: Nonisolated
System (Energy)
•
The primary mathematical representation of
the energy analysis of a nonisolated system
is
•
If any of the terms on the right are zero, the
system is an
isolated system
•
The Work-Kinetic Energy Theorem (
K
=
W
) is a
special case of the more general equation above

7.2 Analysis Model: Isolated System
(Energy)
•
Isolated system: no energy crosses the
system boundary by any method
•
Example: lifting a book in a gravitational field
•
System consists of the book and the Earth
•
Mechanical energy:
•
System is isolated, so
•
Mechanical energy is conserved for isolated
system with no noncosernvative forces acting

Problem-Solving Strategy: Isolated System with No
Noncoservative Forces: Conservation of Mechanical
Energy
1. Conceptualize -
Study the physical situation
carefully and form a mental representation of
what is happening.
•
As you become more proficient working energy
problems, you will begin to be comfortable
imagining the types of energy that are changing
in the system.

Problem-Solving Strategy: Isolated System with No
Noncoservative Forces: Conservation of Mechanical
Energy
2. Categorize -
Define your system, which may
consist of more than one object and may or

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