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7 Conservation of Energy and

an Introduction to Energy and Work

Ted Kinsman/Science Source

YOU WILL LEARN TO:
• Explain what it means for a quantity • Describe how the work-energy
to be conserved. theorem relates to conservation of
• Describe what conditions must energy for an object or a system.
be met for work to be done on • Explain the meaning of potential
an object, for both positive and energy and how conservative
negative work. interactions, such as those described
• Explain the relationship between by the gravitational and spring
work and kinetic energy for an object. forces, give rise to potential energy.
• Explain why something modeled • Recognize why the work-energy
as an object can have only kinetic theorem applies even for curved
energy, and why a system can have paths and varying forces such as
other types of energy. the spring force.

The ideas of work and energy are intimately related,
7-1 and this relationship is based on a conservation

principle

In Chapter 1 we introduced system and object; the distinction between these will
be foundational to our understanding of energy. In Chapters 2 and 3, we learned to
describe the motion of an object, with some guidance on how that description is a
simplification for the motion of a system. In Chapters 4 and 5, we explored how to
use the concept of force to describe the interactions between objects and systems. In
this chapter, we will begin applying one of the most fundamental ideas (and one of the
NEED TO REVIEW? most useful tools) in physics: The changes that occur as a result of interactions between
Turn to the Glossary in the objects and systems are constrained by conservation laws.
back of the book for definitions What does this mean? Conservation is often a poorly understood concept because
of bolded Key Terms. of the use of the word in everyday life. We all try to conserve energy, switching off
the lights when we leave a room, or turning down the thermostat in the winter. When
we use the word conservation in science, however, we mean something much more pro-
found than “using less.” In science, a conserved quantity is a quantity that can be trans-
ferred between objects or systems, or converted from one type to another, but is neither
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Uncorrected proofs have been used in this sample. Copyright © Bedford, Freeman & Worth Publishers.
Distributed by Bedford, Freeman & Worth Publishers. For review purposes only. Not for redistribution.

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