Encyclopedia of Energy Volume IV (Encyclopedia of Energy Series)

802 Pages·2004·18.477 MB·English

by  Robert U Ayres, Robert Costanza, Jose Goldemberg, Marija D Ilic, Eberhard Jochem, Robert Kaufmann, Amory B Lovins, Mohan Munasinghe, R K Pachauri, Claudia Sheinbaum Pardo, Per Peterson, Lee Schipper, Margaret Slade, Vaclav Smil, Ernst Worrell, Cutler J. Cleveland

Mechanical Energy
JOSEPH PRIEST
Miami University
Oxford, Ohio,United States
The physical concepts of work, kinetic energy as
1. Mechanical Energy energyduetomotion,andpotentialenergyasenergy
2. Work due to some favorable position are discussed in this
3. Kinetic Energy article. Added together, kinetic energy and potential
4. Work–Energy Principle energy are called mechanical energy. In the absence
ofnonconservativeforces(e.g.,friction),themechan-
5. Conservative andNonconservative Forces
ical energy of an object does not change with time
6. Potential Energy
andissaidtobeconserved.Themotionofachildon
7. Conservation ofMechanical Energy
a swing is discussed in light of the conservation of
8. EnergyConversion
energy. Awide variety of important types of kinetic
9. Applications ofMechanical Energy
energy are derived from the conversion of other
forms of energy. Such is the case in a hydroelectric
Glossary system that is discussed in some detail in the article.
conservative force When the net work done by a force is
zero forevery paththatendsup atthe starting point.
energy The capacity or ability of an object to do work, 1. MECHANICAL ENERGY
with thejoule(J)as the measuringunit.
Hooke’s Law When an elastic object exerts a force
Energy has some meaning to everyone. A person
proportional to the displacement of the object and in
often does not have energy following a bout with a
theopposite direction.
joule(J) Theunitofworkandenergy;aforceof1newton cold. Concerns about depletion of our energy
(N) actingover a distanceof1m does1J of work. resources, solar energy, wind energy, and nuclear
kinetic energy The ability of an object to do work as a energy are common topics in newspapers and on
result of having mass and speed; in terms of mass (m) television.Althoughenergyhasseveralmeanings,ina
andspeed (v),kineticenergy is1mv2: physical sense it is considered ‘‘a capacity for doing
2
mechanical energy The sum of the kinetic energy and work.’’Anobjectcanhaveacapacityfordoingwork
potential energy ofanobject.
due to its motion and by virtue of an advantageous
nonconservativeforce Whenthenetworkdonebyaforce
position. The combination of these two types of
isnotzero ina paththat endsupatthe starting point.
energy is called mechanical energy. The implications
potential energy The ability of an object to do work as a
ofmechanicalenergyaretiedtothemeaningofwork.
result of anadvantageousposition.
power The rate of doing work or converting energy; the
watt (W) is the metric measuring unit, where 1W is
equal toa rateof 1Jper second. 2. WORK
restoringforce Aforceonanobjectthattendstorestorethe
objecttoitsconditionpriortoapplicationoftheforce.
A person does physical work when cleaning a room.
watt (W) A rate of doing work or converting energy; the
A student does mental work when preparing for an
wattisthemetricmeasuringunit,wherearateofdoing
exam. Whether physical or mental, work involves
work of1J per secondisa watt ðP¼work=tÞ:
an effort directed toward producing some outcome.
work Theresultofaforceactingonanobjectastheobject
movesfromonepositiontoanother;inone-dimensional In the physical sense, effort is associated with force
motion, work is the product of the force (F) and (pushorpull),andworkisdonewhenaforceactson
displacement(d). an object as it moves through some distance. The
EncyclopediaofEnergy,Volume4.r2004ElsevierInc.Allrightsreserved. 1
2
MechanicalEnergy
Force (F ) Force (F )
Initial position Later position
Displacement (d )
FIGURE1 Illustrationshowingacarmovingtotherightthathasbeendisplacedbyanamountd.Duringthedisplacement,
thepersonexertsaforceFtotheright.Thework(W)donebythepersonistheproductofforceanddisplacement(W¼Fd).
The net work on anobjectisthe algebraicsum of
the works done by each force acting on the object.
Supposethatasledmoves2meastwardasaresultof
a girl pulling due east with a force of 100 N and a
East boy pulling due west with a force of 50 N. The girl
does
FIGURE2 Illustrationshowingacartravelingeastthatisaided
byapersonpushingeastandhinderedbyapersonpushingwest. þ100 N(cid:5)2m¼200 J of work;
Theworkdonebythepersonpushingeastispositive.Thework
the boy does
donebythepersonpushingwestisnegative.
(cid:6)50 N(cid:5)2m¼(cid:6)100 Jof work;
person cleaning a room does work on the broom by
and the net amount of work is
displacing it through some distance. In the simplest
situation,thedirectionoftheforceiseitherthesame þ200 J(cid:6)100J¼þ100 J:
asthedirectionofthedisplacementoroppositetothe
directionofthedisplacement.Thisbeingthecase,the
3. KINETIC ENERGY
numericalvalueofthework(W)istheproductofthe
force (F) and the displacement (d) (Fig.1):
Adaydoesnotpasswithoutapersonbeinginvolved
W ¼Fd ð1Þ in physical work. The forces that move one in
walking and running perform work. Lifting food to
Measuringforceinnewtons(N)anddisplacementin
one’s mouth and chewing food involves forces doing
meters (m) gives work the units of newton-meters.
work.Onsomedays,apersonworksmoreeasilyand
One newton-meter is called a joule (J).
more efficiently than on other days. One’s activities
The physical definition of work retains much of
maybecastintermsofhisorherabilitytodowork.
the popular notion with one important difference.
Because physical work involves forces and move-
No matter how much force (effort) is exerted, no
ment, one might ask, ‘‘Under what conditions does
work is done in the physics sense if the object does
something have a capacity for moving an object
not move. A person may fret and sweat while
through some distance?’’ A car in motion has this
pushing on a heavy box, but no work is done if the
capacity because if it slams into the rear of a car
box does not move.
stoppedataredlight,thestruckcarwillsurelymove
Aforceinthesamedirectionasthedirectionofthe
some distance. The energy associated with masses in
movement produces an effect that is very different
motion is called kinetic energy. A big car colliding
from that if the directions were opposite. A person
with a stopped car will ‘‘do more work’’ on the
pushing eastward on a car moving eastward tends to
stoppedcarthanwillasmallervehiclecollidingwith
helpthecaralong(Fig.2).However,apersonpushing
a stopped car. Similarly, a fast-moving car colliding
westward on the same car tends to slow the car. We
with a stopped car will ‘‘do more work’’ on the
distinguish these two situations by labeling the work
stopped car than will a slow-moving car of the same
as‘‘positive’’whenforceandmovementhavethesame
type colliding with a stopped car. A numerical
directionandas‘‘negative’’whenforceandmovement
evaluation of kinetic energy should reflect these
have opposite directions. The car is moving eastward
observations. Formally, the kinetic energy (K) of an
underthe action of one personpushing eastwardand
objecthavingmassmmovingwithspeedvisdefined
another person pushing westward. The person push-
asone-halfthe productofmassandsquareofspeed:
ing eastward does positive work. The person pushing
K¼1mv2: ð2Þ
westward does negative work. 2
3
MechanicalEnergy
Both energy and work are measured in joules. lifter because the force and movement are in the
Importantly, Eq.(2) shows that kinetic energy samedirection.Thegravitationalforcedoesnegative
increases if the mass and/or the speed increase. work because the force and movement are in
Doubling the mass of an object while keeping its opposite directions. If the person lowers the box
speed the same will double the kinetic energy. backtothefloor,thegravitationalforcedoespositive
Doubling the speed of an object while keeping its work becausetheforceandmovementnowhavethe
massthesamewillincreasethekineticenergybyfour samedirection.Thenegativeworkdonebygravityin
times. The dependence on speed is especially the upward movement is equal in magnitude, but of
significant. opposite algebraic sign, to the work done by the
gravitational force in the downward movement.
Accordingly, the net amount of work done by the
4. WORK–ENERGY PRINCIPLE gravitational force in the round trip of going up and
back down is zero. When the net amount of work
Atsometime,anobjectsuchasacarmayhavespeed donebyaforceinanytripthatendsupatthestarting
v and kinetic energy K¼1mv2: Later, its speed may point is zero, the force is said to be conservative. If
2
change to V so that its kinetic energy is 1mV2: The thenetamountofworkdonebyaforceinatripthat
2
change in kinetic energy is the later value minus the ends up at the starting point is not zero, the force is
earliervalue,thatis,1mV2(cid:6)1mv2:Thework–energy said to be nonconservative. A friction force is a
2 2
principle states that the net amount of work on the nonconservative force. A friction force acting on an
object between the initial and later times is equal to objectalwaysopposesitsmovementsothatthework
the change in kinetic energy: due to friction is always negative. Consequently, the
W ¼1mV2(cid:6)1mv2: ð3Þ net work due to friction in a trip that ends up at the
net 2 2 starting point is never zero.
Whenahockeyplayerhitsastationary0.16-kgpuck
with a hockey stick and imparts to it a speed of 45
m/s (100 miles per hour [mph]), its kinetic energy
6. POTENTIAL ENERGY
changes from zero to 1 ð0:16 kgÞð45 m=sÞ2 ¼
2
þ162J: The change in kinetic energy is þ162J–
When an object such as a box is in an elevated
0J¼ þ162J,andthenetworkis þ162J.Theglove
position, it has ‘‘a capacity for doing work’’ because
of a baseball catcher receiving a 0.15-kg baseball
if it is dropped and hits something, it can exert a
traveling 40m/s (90mph) reduces the speed of the
force on that something and push it through some
baseball to zero. The change in kinetic energy of the
distance.Theboxatanelevatedheightisanexample
ball is 0 J(cid:6)1ð0:15 kgÞð40 m=sÞ2 ¼(cid:6)120J; and the
2 of potential energy. Potential energy is associated
net work is (cid:6)120J.
withconservativeforces.Bydefinition,thechangein
You see this principle in operation in many
potential energy when moving from one position to
processes. The kinetic energy of water flowing over
another is the negative of the work done by the
adamincreasesasitsspeedincreases.Theincreasein
conservative force acting during the change in
kinetic energy is the result of positive work done on
position. Labeling U the potential energy and DU
the water by the gravitational force. When a car
the change in potential energy, the definition may be
startingfromrestissetintomotion,itskineticenergy
expressed as
increases. This is due to work done by a force in the
directionofmotionofthecar.Likewise,whenthecar DU¼(cid:6)Wconservative: ð4Þ
slows down, its kinetic energy decreases. This is due
to (negative) work by a force on the car acting in a
6.1 Gravitational Potential Energy
direction opposite to the direction of motion.
The gravitational force on a box of mass m is mg,
where g is the acceleration due to the gravitational
5. CONSERVATIVE AND
force.Iftheboxisraisedaheighth,theworkdoneby
NONCONSERVATIVE FORCES gravityisW¼(cid:6)mgh.Thechangeinpotentialenergy
of the box is then DU¼(cid:6)W ¼þmgh. The
conservative
A box being lifted from the floor is acted on by an positive sign means that the potential energy has
upwardforceprovidedbythelifterandadownward increased. When the box falls from the height h, the
force due to gravity. Positive work is done by the work done by gravity is positive and the change in
4
MechanicalEnergy
potential energy becomes DU¼(cid:6)mgh; the potential 7. CONSERVATION OF
energy has decreased. The potential energy acquired MECHANICAL ENERGY
by the box by placing it in an advantageous position
can be recovered by letting it drop to its initial
Frictionisalwayspresentinamechanicalsystem,but
position on the floor. Water atop a dam in a
if it can be ignored, the mechanical energy (i.e., the
hydroelectricplanthaspotentialenergy.Whenitfalls
sum of the kinetic energy and potential energy) does
toward the bottom of the dam, it loses potential
not change with time. To illustrate, a girl waiting to
energy but gains kinetic energy. At some point, the
move down a playground slide has potential energy
waterdoesworkbypushingonthebladesofawater
but no kinetic energy because she is at rest. Moving
turbine, and the kinetic energy of the water is
down the slide, she loses potential energy but gains
converted to rotational energy of the turbine.
kinetic energy. If friction between the girl and the
slide can be ignored, the mechanical energy at any
momentisunchanged.Atthebottomoftheslide,all
6.2 Elastic Potential Energy
of her initial potential energy would have been
A material is said to be elastic if it returns to its converted to kinetic energy. The constancy of
original condition after being stretched or com- mechanical energy is called the conservation of
pressed. A spring, a rubber band, the bow of a bow mechanical energy.
and arrow, and a shock absorber on a car are To the extent that friction can be ignored, the
examples of elastic objects. Somewhat like the earth mechanical energy of a child on a swing is constant
pulling downward on a box that is being lifted at any moment (Fig.3). Held in an elevated position
upward, an elastic object pulls in an opposite waiting for the swing to begin, the child has only
direction to the force that is stretching or compres- potential energy. When released, the child gradually
sing it. The object has potential energy in the loses potential energy but gains kinetic energy. The
stretchedorcompressedconditionduetoitscapacity sumofthetwoenergiesisunchangedatanymoment.
to do work if it is released. For many elastic objects, At the lowest portion of the swing, the potential
the force exerted by the object, called the restoring energy is zero, making the kinetic energy a max-
force, is proportional to the extension or compres- imum. As the swing moves upward from the lowest
sion and in a direction opposite to the extension or position, the child gradually gains potential energy
compression.Thisbeingthecase,theobjectissaidto but loses kinetic energy. The child is momentarily at
obey Hooke’s Law. A force obeying Hooke’s Law rest at the uppermost position of the swing, making
may be expressed as the kinetic energy zero and the potential energy a
maximum. If friction were absent, the back-and-
F ¼(cid:6)kx; ð5Þ forth motion would continue unabated andmechan-
ical energy would be conserved at any moment. But
whereFistheforceexertedbytheelasticobject,xis as anyone who has taken a child to a playground
the extension or compression, and k represents the knows, friction is always present and the motion
strength of the force. For a linear spring, k is called graduallydiesoutunlessthepersonpushestheswing
the spring constant having units of newtons per to replace the energy lost to friction.
meter. The stronger the spring, the larger the spring
constant. The potential energy of a spring obeying
Hooke’s Law is given by
8. ENERGY CONVERSION
U¼1kx2: ð6Þ
2
Anobjectinanelevatedpositionclearlyhaspotential
Elastic potential energy is used in many ways. The energy because if it is dropped and contacts some-
kinetic energy acquired by an arrow has its origin in thing duringitsdownward flight,itmaydowork on
the elastic potential energy in the flexed bow. Pole that something. Similarly, a compressed spring has
vaultersacquiremuchoftheirvaultfromabentpole. potentialenergybecauseifitisreleased,itmaystrike
Toy guns expel projectiles by releasing the elastic something and do work on it. The general idea of
potential energy of a compressed spring. Atoms in a potentialenergyasacapacityfordoingworkandthe
molecule are held together by spring-like forces that rearrangementofthingswhenthepotentialenergyis
lead to a form of potential energy. Release of that converted goes beyond these two mechanical cases.
potential energy often leads to the emission of light. Forexample,gasolinehaspotentialenergybecauseif
5
MechanicalEnergy
At the start At the highest point
P.E. is maximum P.E. is maximum
K.E. is zero K.E. is zero
At the lowest point
P.E. is zero
K.E. is maximum
FIGURE3 Illustrationshowingthat,totheextentthatfrictioncanbeignored,themechanicalenergyofachildinaswing
isunchangedatanymoment.P.E.,potentialenergy;K.E.,kineticenergy.
agasolinevapor/airmixtureisignitedinthecylinder gravitational potential energy. Motors convert elec-
of an internal combustion engine, the expanding gas tric energy to rotational kinetic energy. Whether
pushesagainstapistonanddoesworkonit.Theroot large or small, and whether simple or complex,
ofthepotentialenergyisfoundinthemoleculesfrom converters producing kinetic energy all subscribe to
which the gasoline is formed. Energy is extracted the principle of conservation of energy. Each one
from these molecules when their atoms are rear- converts energy into some form of kinetic energy
ranged into different molecules during the combus- regarded as useful, and each one diverts energy that
tion process. Similarly, the uranium fuel in a nuclear is not immediately useful and might never be useful.
reactor has potential energy that is extracted from Because energy is diverted, the efficiency defined as
rearrangement of neutrons and protons through
useful energy
nuclear fission reactions. The energy produced from efficiency¼
total energy converted
the nuclear reactions is then used to produce steam,
which pushes against the blades of a turbine, can never be 100%.
producing rotational kinetic energy.
An industrial society finds myriad uses for kinetic
energy. Pistons moving up and down in an internal 9. APPLICATIONS OF
combustion engine have kinetic energy. Wheels
MECHANICAL ENERGY
rotating on an automobile or a truck have kinetic
energy. Water falling from atop a dam has kinetic
9.1 Pile Driver
energy. Around a home or in a factory, there are
numerousmotorsprovidingrotationalkineticenergy Apileisalargemetalorwoodenpostdrivenintothe
foramultitudeofpurposes.Inalloftheseexamples, ground. A pile driver (Fig.4) lifts a rather massive
the kinetic energy evolves from a conversion from object (hammer) above the pile and drops it. Each
some other form of energy. The force behind the drop of the hammer drives the pile farther into the
movement of a piston comes from an expanding gas ground until the required depth is reached. Lifting
produced by the ignition of a gasoline/air mixture. the hammer requires mechanical work. In so doing,
The kinetic energy acquired by water rushing to the the hammer acquires potential energy. When re-
bottom of a dam comes from a conversion of leased, the hammer gradually loses potential energy
6
MechanicalEnergy
Inahydroelectricpowerplant,theturbinewoulddrive
anelectricgeneratorandtheenergy(E)wouldbeused
Hammer for generating electricity.
Hammer
guide
9.3 Pumped Storage Hydroelectric System
Pile The demand for electric energy by a community
varieswiththetimeofdayandwiththetimeofyear.
An electric power utility must be prepared to meet
these demands. This poses an engineering problem
because there is no practical method of storing
FIGURE4 Basiccomponentsofapiledriver.
electricenergyonascalethatwillmeetthedemands
of a large community. To meet short-term increases
in demand, electric utilities employ generators that
and gains kinetic energy. Work is done on the pile
can be turned on and off on short notice. For
duringcontact,causingthekineticenergytodecline,
example, they may use a gas turbine similar to a jet
eventually to zero.
plane engine to drive a generator. Another scheme is
touseapumpedstoragehydroelectricsystem.Sucha
9.2 Hydroelectric System systemdoesnotrelyonnaturetoreplenishthewater
in a reservoir but rather uses electrically run pumps.
Wheneveranobjecthasgravitationalpotentialenergy,
Importantly, the system can generate electricity on
some agent had to do work on the object. In the case
short notice. A schematic diagram of the system is
of a pile driver, there is a hoist of some sort. Water
shown in Fig.6. Water is forced to an elevated
atop a dam has potential energy. Nature provides the
reservoirbyamotor-driventurbine.Thewaterinthe
means to fill the water reservoir through evaporation
reservoir has gravitational potential energy by virtue
followed by condensation and rain. To see the energy
of the work done on it. When electricity is needed,
transformations involved when the water falls from
the water is allowed to flow downward into the
the top of the dam onto the blades
turbine that drives the motor, which now functions
of a turbine, it helps to visualize the motion of an
as an electric generator. The energy required to
object having boundaries. Accordingly, imagine the
elevatethewaterisnevercompletelyrecoveredinthe
motion of a cube of water moving with the stream
process. Nevertheless, the system is economical
(Fig.5). At the top of the dam, the cube of water of
mass(m)andspeed(V)haskineticenergy(cid:1)1mV2(cid:2);and because the reservoir can be filled when electric
2 energy demands and costs are low. It is also possible
potentialenergy(mgh)duetoitspositionatthetopof
to have a system in which water flows from ground
thedam.Asthegravitationalforcepullsthecubefrom
leveltoundergroundturboelectricgenerators.Inthis
the top of the dam to the bottom, it
case, work has to be done to restore the water to
loses potential energy but gains kinetic energy. At
ground level.
the bottom of the dam, all of the potential energy
(mgh) has been converted to kinetic energy (cid:1)1mv2(cid:2):
2
Thetotalkineticenergynowincludesitskineticenergy 9.4 Warning
beforefallingplusthekineticenergygainedbyfalling:
Steelisaveryhardmetalthatbehaveslikeaverystiff
12mv2 ¼12mV2þmgh: ð7Þ spring when compressed or stretched. Bolting two
steel plates together compresses each plate to some
The cube of water arrives at the paddle wheel with
energy (cid:1)1mv2(cid:2): The force of the cube on the paddle extent. Although the compression may be small, the
2 elastic potential energy (cid:1)1k x2(cid:2) in the plates can be
wheel causes work to be done on the wheel. 2
large because the spring constant (k) is large. If the
Accordingly, the paddle wheel rotates, acquiring
nutontheboltholdingtheplatestogetherisreleased
energy(E)whilethecubeofwaterloseskineticenergy.
gradually, the elastic potential energy declines
The kinetic energy of the cube after it passes by the
gradually. But if for some reason the nut cannot be
paddle wheel (K) equals the kinetic energy it had
turned and the bolt is freed by chiseling the bolt in
before striking the paddle wheel minus the energy
two, the elastic potential may be released suddenly,
acquired by the paddle wheel:
causing the nut to spring away. So violent is the
K¼1mv2(cid:6)E ð8Þ
2 separation that a person may be seriously injured if
7
MechanicalEnergy
1mv 2 + mgh
2
1
1mv 2 = 1mv 2 + mgh 1mv 2 − E
2 2 2
2 E 3
FIGURE5 Energytransformationsinvolvedinwaterflowingoveradam.(Position1)Atthetopofthedam,thecubeof
waterhaskineticenergy(cid:1)1mv2(cid:2)duetoitsmotionandpotentialenergy(mgh)duetoitspositionabovethebottomofthedam.
2
(Position2)Atthebottomofthedam,allofthepotentialenergy(mgh)hasbeenconvertedtokineticenergy.Theenergyofthe
cubeofwateriskinetic(cid:1)1mv2(cid:2)andincludesthekineticenergyithadatthetopofthedamplusthekineticenergyacquiredby
2
fallingoverthedam.(Position3)Passingbythepaddlewheel,thecubeofwatertransfersenergy(E)tothewheel.Itsenergy
afterpassingthewheelisstillkineticandisequaltoitsenergybeforeimpingingonthewheel(cid:1)1mv2(cid:2)minustheenergy(E)
2
impartedtothewheel.
Electricity to
consumers
Electricity
transmission
lines
Electric
power
station
Water reservoir
Electrical wires
from generator to
power station
Motor-generator Valve
River or stream
Turbine
FIGURE 6 Principleofapumpedstoragehydroelectricsystem.Waterinanelevatedreservoirhaspotentialenergyasa
result of being pumped from a river or stream. Electricity is generated when the water flows through a turbine–generator
combinationonitswaybacktotheriverorstream.
heorshehasthemisfortuneofencounteringthenut. (cid:7) Storage of Energy, Overview (cid:7) Thermodynamic
Such incidences have actually happened and have Sciences, History of (cid:7) Thermodynamics, Laws of (cid:7)
prompted warnings to workmen who may have to Work, Power, and Energy
free a frozen nut.
Further Reading
SEE ALSO THE
Hobson,A.(2002).‘‘Physics:ConceptsandConnections,’’3rded.
FOLLOWING ARTICLES PrenticeHall,UpperSaddleRiver,NJ.
Priest,J.(2000).‘‘Energy:Principles,Problems,Alternatives,’’5th
Conservation of Energy Concept, History of (cid:7) ed.Kendall/Hunt,Dubuque,IA.
Serway, R. A., and Beichner, R. J. (2000).‘‘Physics for Scientists
Electrical Energy and Power (cid:7) Energy in the History
andEngineers.’’Brooks/Cole,PacificGrove,CA.
andPhilosophyofScience(cid:7)FormsandMeasurement Serway,R.A.,andFaughn,J.S.(1999).‘‘CollegePhysics.’’Brooks/
ofEnergy(cid:7)HeatTransfer(cid:7)HydropowerTechnology Cole,PacificGrove,CA.
Media Portrayals of Energy
JAMES SHANAHAN
Cornell University
Ithaca, New York, United States
power sensitized society to the potential importance
1. Introduction of conserving energy. These issues were also fre-
2. Media Coverageof Energy:History quentlymentionedinthemedia.Intheseearlierdays
oftheenvironmentalmovement,itwasbelievedthat
3. PublicOpinion about Energy
mass media could be prominent tools to encourage
4. Media Effectson PublicOpinion andPolicy
conservation of energy, through adoption of energy-
saving measures in the home, driving smaller and
more fuel-efficient vehicles, and promoting alterna-
Glossary
tive energy source use. The attitudes of this period
environmentalism A social movement of the 20th century highlightedthefactthatmediacanplayanimportant
focusing on the threats to human health posed by a
roleinpeople’sindividualchoices.Influencessuchas
variety of pollutants. Includes a broad swath of
advertising, journalism, television programs, and
concerns, such as air and water pollution, climate
othermedianeedtobeconsideredwhendetermining
change, wilderness protection, endangered species
how people make choices in energy use behavior.
protection, andsustainability.
massmedia Thesystemofcommunicationbywhichlarge,
commercial organizations produce entertainment and
news content for large, heterogeneous audiences. The
term usually includes television, radio, newspapers/ 1. INTRODUCTION
magazines,popular music,publishing,and films.
muckraker A name for a type of investigative newspaper In general, the influence of media on energy use has
or magazine journalist of the early 20th century.
been considered within the wider field of study of
Muckrakersexaminedsocialproblems,workingcondi-
media effects on environmental concerns. This field
tions, environmental pollution, and other threats
ofresearchhasshownthatmediadohavebothdirect
associated with theactivityof largeindustry.
andindirectimpactsonhowpeopledevelopconcep-
public opinion A collective indication or measurement of
tions of the environment. However, these effects are
how the public feels about given issues. Usually
measured using scientific random sampling techniques not always consistent; they do not always move in
and opinion questionnaires or surveys. The term also the same direction. Thus, it has been shown
refers to a more general, impressionistic perception of repeatedly that information derived from the media
publicsentiment ona givenissue. is an important factor in how people develop
awareness about the environment. Because people
directly experience only a small portion of the
The mass media, especially newspapers, magazines, environment,knowledgeaboutglobalenvironmental
television,andmovies,playaroleintheportrayalof issues and problems must come from mediated
energy issues. Since the energy crisis of 1973, the sources. People who are more attentive to news-
attention of scholars has been turned to how media papers and other journalistic sources are more likely
shape, frame, and influence audience perceptions of to be informed and knowledgeable about environ-
energy and the environment. During the period mental issues and problems. Those who are particu-
following the energy crisis, especially throughout larly attentive to environment-specific media sources
the 1980s and early 1990s, issues of energy (such as environmental magazines or television
conservation were frequent topics of scholars’ atten- programs) are better informed about environmental
tion. Oil crises and the perceived dangers of nuclear issues and are more concerned about them. On the
EncyclopediaofEnergy,Volume4.r2004ElsevierInc.Allrightsreserved. 9
10
MediaPortrayalsofEnergy
other hand, general media attention (especially to firmly cemented after the Civil War. How did this
entertainment media) is associated with less knowl- affect coverage of energy issues?
edge and concern about environmental issues.
Frequent viewers of television programs, for in-
2.1 Coal and Oil
stance,arelessconcernedaboutenvironmentalissues
in general. Further, they are more supportive of Attitudesaboutsourcesofenergysuchascoalandoil
materialist ideologies that tend to promote higher are recoverable from publications of the 19th
energy consumption. century, which followed the development of new
Thesecountervailingexamplesshowthatitcanbe energy sources with close attention. However, as
dangerous to lump all ‘‘media’’ together under one with media coverage of any major issue, it is not
umbrella. Sometimes media outlets promote con- possible to determine a single prevailing attitude
servationofenergyandconcernfortheenvironment; toward an energy source such as coal or oil.
specific campaigns aimed at reducing energy con- Certainly, many of the major media sources adhered
sumption are often studied with this as the goal. toagenerallynationalisticideology,orientedtoward
Meanwhile, a more general attitude of promotion of goals such as economic progress, westward expan-
consumption seems to guide the overall media sion, and even imperial aspirations. Within this
atmosphere, which is built on advertising-supported context, fossil fuel sources obviously played an
ideologies of material growth. Given these tenden- important role in the development of America as a
cies, it is necessary to try to disentangle the various world power. Thus, one major current of the media
mediaeffects,inordertogetsomeideaaboutthekey mainstream was oriented toward a view of fossil
questions of interest. The main question that is the fuels as expanding the possibilities for America,
focusinthisarticleconcernshowthemediainfluence withoutworryingtoomuchaboutpotentialnegative
public conceptions of energy within an environmen- consequences.
tal framework. But worrisome themes also appeared in the press.
Theeconomicboomsandbustsofoildiscoverieswere
linked to boom-and-bust media cycles: high-hoped
optimism followed by cautionary tales was a not
2. MEDIA COVERAGE OF
uncommon cycle in the press. Stories told of those
ENERGY: HISTORY who made and lost fortunes were as characteristic of
newscoverageintheoilyearsastheywereinthedays
Beforediscussingcurrentissuesinmediacoverageof followingtheInternetbubble.Oilwasoftenpresented
energy, some of the main historical aspects of how as something ridiculously easy to obtain and sell,
media have treated the energy issueare summarized. violatingallpreviousrulesofthemarketplace.Aftera
This discussion will be contexted within the wider boom had gone bust, the national dailies turned to
theme of how the media treat the environment. tales of woe and ghost towns in their coverage.
It is a common conceptionthat environmentalism As oil became an industry, it attracted a different
in the public mind and in the media frame is a kind of attention, that of the ‘‘muckrakers.’’ Muck-
phenomenon of the latter 20th century. However, rakers were the forerunners of today’s ‘‘investigative
there are clear examples of how the mass media journalist.’’ Their reformist spirit led them to attack
providedastageforadiscussionofenvironmentand industry on issues ranging from child labor to food
energy issues well back into the 19th century. safety to environmental issues. Ida Tarbell (see
Preservationists such as John Muir, for example, Fig.1), writing in the pages of McClure’s, a national
wereusingthenationalmediaintheirattemptstoset magazine,attackedtheStandardOilCompanyforits
aside lands for national parks. Muir’s articles in monopolisticandpredatorypractices.Herfamilylife
magazinessuchasCentury attractedthe attentionof in the Pennsylvania oil patch had been disrupted by
Eastern elite audiences to issues that were mainly Rockefeller’s South Improvement scheme. Published
situated in the West. These strategies helped develop serially from 1902 to 1904, Tarbell’s ‘‘History of
national attention for environmental issues in the Standard Oil’’ is considered a founding piece of
context of a nationally emerging mass media investigative journalism. But not all media contro-
structure. Though a national mass media system versies resulted in immediate change. Concerns
had emerged as early as the 1830s, especially with about ethyl leaded gasoline were covered fairly
the development of mass newspapers in major cities extensively, especially in the New York City area,
served by wire services, this structure was most from 1924 to 1926. Worker deaths from lead
11
MediaPortrayalsofEnergy
century, but the atmospheric impacts of fossil fuel
consumption began receiving a closer look in the
media in the 1960s. This peaked with the passage of
national environmental legislation (the National
Environmental Protection Act) in 1970.
FossilfuelsandAmericanindustryingeneralcame
under further media scrutiny in the 1960s. Rachel
Carson’s Silent Spring (1962), though not focused
directlyonfuelsorenergysources,drewattentionto
the chemical industry and its promotion of danger-
ouschemicalssuchasdichlorodiphenyltrichloethane
(DDT). Silent Spring sensitized Americans to risks
both known and unknown in and about the general
environment. Carson arguably inaugurated the age
of environmentalism, in which the media played an
important role in turning people’s attention to a
variety of environmental issues, with fossil fuel
consumption at or near the top of the list of
problems. Carson’s book, serialized in the New
Yorker magazine, received wide media attention,
building on the earlier model for journalistic crusad-
ing that had been successfully tested by both John
FIGURE 1 IdaTarbell(1857–1944). Muir and Ida Tarbell.
This touched off a frenzy of popular publishing
poisoning led crusading scientists to point out that activity focused on energy consumption and envir-
leadadditivescouldbeharmfultothepublicatlarge, onmental issues. Books such as The Waste Makers
due to risks from lead deposition in exhaust. (Vance Packard, 1960), The Quiet Crisis (Stewart
Although a committee was formed by the Surgeon Udall, 1963), The Population Bomb (Paul Ehrlich,
General to look at the issue, no action was taken, 1968), The Closing Circle (Barry Commoner, 1971),
evenwithsignificantattentionfromnewspaperssuch The Limits to Growth (Donella Meadows et al.,
astheNewYorkWorldandTheNewYorkTimes.It 1972), The Poverty of Power (Barry Commoner,
was not until the 1970s that the Environmental 1975), The Eco-Spasm Report (Alvin Toffler, 1975),
Protection Agency (EPA) would take action to and The Fate of the Earth (Jonathan Schell, 1985)
remove lead from gasoline. Still other themes were are examples of popular publications that made
developed earlier than one might expect. Recogniz- some impact on public sensibilities and opinions
ing American dependence on oil led to journalistic about energy consumption problems. These efforts
callsforconservationanddevelopmentofrenewable were strengthened by press attention to the oil crises
energy sources long before the onset of the environ- of the 1970s, which caused a great deal of concern
mental era in the 1970s. The concern was not about energy dependence. With energy issues boun-
environmental in nature, but stemmed from a worry cingaroundthepressthroughoutthe1970s,theissue
about maintaining America’s preeminence despite was often at the top of the public agenda, particu-
dependence on oil. larlywhengasolinepriceswererising.Withacastof
Typically,mediaattentiontoenvironmentalissues villainous characters [the Organization of Petroleum
is driven by both journalistic cycles and events. Exporting Countries(OPEC) oil sheiks]andan issue
Events are spectacular disasters or phenomena with striking at the heart of the American economy,
widespread impact. A ‘‘killer smog’’ in Donora, foreignoilwasthebiggestnewsitemin1973,andto
Pennsylvania in 1948 drew enough media attention alesserextentin1979.However,specificeventsalso
to catalyze the development of smoke-abatement masked cycles of press concern about energy issues.
programsincitiesaroundtheUnitedStates.Thiswas These cycles are generated not by specific external
anearlyprecursortothemorefar-reachingprograms motivating factors, but by tendencies to adhere to
of air pollution control that were eventually enacted narrative structure embedded within journalistic
in the 1970s. Indeed, air pollution themes had practice. For instance, in the late 1980s and early
received sporadic attention throughout the 20th 1990s,journalistsinbothnewspapersandmagazines