Chapter 15 Energy. 15.1 Energy and its FormsEnergy 15.1 Energy and its Forms Work is done when a force moves an object through a distance. Energy

Chapter Chapter 1515

EnergyEnergy

15.1 Energy and its Forms15.1 Energy and its Forms EnergyEnergy

15.1 Energy and its Forms15.1 Energy and its Forms

Work is done when a force moves an Work is done when a force moves an object through a distance. object through a distance.

Energy is the ability to do work. Energy is the ability to do work. Energy is transferred by a force Energy is transferred by a force

moving an object through a distance. moving an object through a distance.

Energy and Work


Work and energy are closely related. Work and energy are closely related. When work is done on an object, When work is done on an object,

energy is transferred to that object. energy is transferred to that object. Work is a transfer of energy. Work is a transfer of energy.


Both work and energy are measured Both work and energy are measured in joules. in joules.

The work done when an object is The work done when an object is moved 1 meter by a 1-newton force moved 1 meter by a 1-newton force equals 1 joule. equals 1 joule.

Although energy can take many Although energy can take many forms, it can always be measured in forms, it can always be measured in joules.joules.


Many forms of energy can be Many forms of energy can be classified into two general types:classified into two general types:• kinetic energy kinetic energy • potential energypotential energy


Kinetic EnergyKinetic Energy

The energy of motion is called kinetic The energy of motion is called kinetic energy. (Greek energy. (Greek kinetoskinetos means means moving). moving).

The kinetic energy of any moving The kinetic energy of any moving object depends upon its mass and object depends upon its mass and speed. speed.

KE=½mvKE=½mv22






Potential EnergyPotential Energy

Potential energy is energy stored as Potential energy is energy stored as a result of position, (a result of position, (conditioncondition), or ), or shape. shape.

Two forms of potential energy areTwo forms of potential energy are• gravitational potential energy gravitational potential energy • elastic potential energyelastic potential energy


Gravitational Potential EnergyGravitational Potential Energy Potential energy that depends upon Potential energy that depends upon

an object’s height is called an object’s height is called gravitational potential energy (PEgravitational potential energy (PEgg). ).

This type of energy increases when This type of energy increases when an object is raised to a higher level. an object is raised to a higher level.


An object’s PEAn object’s PEgg depends on its mass depends on its mass (in kg), its height (in m), and the (in kg), its height (in m), and the acceleration due to gravity (9.8 acceleration due to gravity (9.8 m/sm/s22 near Earth’s surface). near Earth’s surface).

PEPEgg=mgh=mgh Gravitational potential energy is Gravitational potential energy is

measured relative to some measured relative to some reference level. reference level.


Elastic Potential EnergyElastic Potential Energy

The potential energy of an object The potential energy of an object that is stretched or compressed is that is stretched or compressed is known as elastic potential energy known as elastic potential energy (PE(PEelasticelastic). ).

An object is said to be elastic if it An object is said to be elastic if it springs back to its original shape springs back to its original shape after it is stretched or compressed. after it is stretched or compressed.

PEPEelastelast=½kx=½kx22. .


k is defined as spring constant and k is defined as spring constant and depends on type of spring materialdepends on type of spring material

x is defined as distance stretched or x is defined as distance stretched or compressedcompressed


Forms of EnergyForms of Energy

All energy can be considered to be All energy can be considered to be kinetic energy, potential energy, or the kinetic energy, potential energy, or the energy in fields such as those produced energy in fields such as those produced by electromagnetic waves. by electromagnetic waves.


The major forms of energy are The major forms of energy are • mechanical energymechanical energy• thermal energythermal energy• chemical energy chemical energy • electromagnetic energy electromagnetic energy • nuclear energynuclear energy

Each of these can be converted into Each of these can be converted into other forms of energy. other forms of energy.


Mechanical EnergyMechanical Energy

The energy associated with the motion The energy associated with the motion and position of objects is mechanical and position of objects is mechanical energy. energy.

Mechanical energy is the sum of an Mechanical energy is the sum of an object’s PE and KE. object’s PE and KE.


Mechanical energy does Mechanical energy does notnot include include thermal energy, chemical energy or thermal energy, chemical energy or other forms of energy associated with other forms of energy associated with the motion or the arrangement of the motion or the arrangement of atoms or molecules. atoms or molecules.


Thermal EnergyThermal Energy

The total potential and kinetic energy The total potential and kinetic energy of all the microscopic particles in the of all the microscopic particles in the object make up its thermal energy. object make up its thermal energy.


Chemical EnergyChemical Energy

Chemical energy is the energy stored Chemical energy is the energy stored in chemical bonds. in chemical bonds.

When bonds are broken, the energy When bonds are broken, the energy is released. is released.


Electric EnergyElectric Energy

Electric energy is the energy Electric energy is the energy associated with electric charges. associated with electric charges.

Batteries convert chemical energy to Batteries convert chemical energy to electric energy. electric energy.

Electric energy also occurs in nature Electric energy also occurs in nature in the form of lightning. in the form of lightning.


Electromagnetic EnergyElectromagnetic Energy

Electromagnetic energy is a form of Electromagnetic energy is a form of energy that travels through space in energy that travels through space in the form of waves. the form of waves.

Travel at Travel at



Nuclear EnergyNuclear Energy

The nucleus of an atom is held The nucleus of an atom is held together by strong and weak nuclear together by strong and weak nuclear forces, which store tremendous forces, which store tremendous amounts of potential energy known amounts of potential energy known as nuclear energy. as nuclear energy.

15.2 Energy Conversion and Cons15.2 Energy Conversion and Conservationervation

EnergyEnergy

15.2 Energy Conversion and 15.2 Energy Conversion and ConservationConservation

Energy can be converted from one Energy can be converted from one form to another in a process known form to another in a process known as energy conversion. as energy conversion.

For example light bulbs convert For example light bulbs convert electric energy into thermal energy electric energy into thermal energy and electromagnetic energy. and electromagnetic energy.

Energy Conversion


EnergyEnergy

Conservation of EnergyConservation of Energy

When energy changes from one form to When energy changes from one form to another, the total energy remains another, the total energy remains unchanged even though many unchanged even though many conversions may occur. conversions may occur.

The law of conservation of energy The law of conservation of energy states that energy cannot be created or states that energy cannot be created or destroyed. destroyed.


EnergyEnergy

In a closed system, the amount of In a closed system, the amount of energy present at the beginning of a energy present at the beginning of a process is the same as the amount of process is the same as the amount of energy at the end. energy at the end.


EnergyEnergy

How Can Energy Change Forms?How Can Energy Change Forms?Rube Goldberg was an award-winning Rube Goldberg was an award-winning cartoonist who drew complex series of cartoonist who drew complex series of devices that performed relatively simple devices that performed relatively simple acts. The devices were arranged so that the acts. The devices were arranged so that the output of one device would act as the input output of one device would act as the input of the next. of the next.


EnergyEnergy


EnergyEnergy

1.1. List at least three kinds of energy List at least three kinds of energy in the device.in the device.2.2. Describe one change, in which Describe one change, in which energy from one form is converted energy from one form is converted into energy of another form.into energy of another form.


EnergyEnergy

Energy ConversionsEnergy Conversions

One of the most common energy One of the most common energy conversions is between potential conversions is between potential energy and kinetic energy. energy and kinetic energy.

The PEThe PEgg of an object is converted to of an object is converted to KE as the object falls. KE as the object falls.

Conversions between KE and PEConversions between KE and PEgg can can happen in both directions. happen in both directions.


EnergyEnergy

Energy Conversion in PendulaEnergy Conversion in Pendula

A pendulum consists of a weight A pendulum consists of a weight swinging back or forth from an arm. swinging back or forth from an arm.

Pendulum clocks make use of the Pendulum clocks make use of the fact that the time it takes for a fact that the time it takes for a pendulum to swing back and forth is pendulum to swing back and forth is precisely related to its length. precisely related to its length.

KE and PE undergo constant KE and PE undergo constant conversion as a pendulum swings. conversion as a pendulum swings.


EnergyEnergy

At the highest point in its swing, the At the highest point in its swing, the pendulum is momentarily motionless as it pendulum is momentarily motionless as it changes direction. changes direction.

At this point, the bob has KE=0 and PEAt this point, the bob has KE=0 and PEgg is is at its maximum. at its maximum.


EnergyEnergy

As the pendulum swings downward, the As the pendulum swings downward, the PEPEgg is converted to KE. is converted to KE.

At the bottom of the swing, KE is at its At the bottom of the swing, KE is at its maximum and PEmaximum and PEgg=0. =0.

The pendulum continues upward and the The pendulum continues upward and the process repeats. process repeats.


EnergyEnergy

The period of a pendulum is the time The period of a pendulum is the time to it takes to make one complete to it takes to make one complete swing and return to its starting swing and return to its starting position.position.

The period (T) depends only on the The period (T) depends only on the length (l) of the pendulum armlength (l) of the pendulum arm

glT 2


EnergyEnergy

Energy Conversion CalculationsEnergy Conversion Calculations

When friction is small enough to be When friction is small enough to be ignored, and no mechanical energy is ignored, and no mechanical energy is added to a system, the mechanical added to a system, the mechanical energy does not change. energy does not change.

MEMEii=(KE=(KEii + Pe + Peii) = (KE) = (KEff + PE + PEff) = ME) = MEff


EnergyEnergy


EnergyEnergy


EnergyEnergy


EnergyEnergy


EnergyEnergy

Energy and Mass Energy and Mass

Einstein’s equation, Einstein’s equation, E=mcE=mc22, says that , says that energy and mass are equivalent and energy and mass are equivalent and can be converted into each other. can be converted into each other.

The law of conservation of energy The law of conservation of energy has been modified to say that mass has been modified to say that mass and energy are always conserved. and energy are always conserved.

15.3 Energy Resources15.3 Energy Resources EnergyEnergy

15.3 Energy Resources 15.3 Energy Resources

Nonrenewable Energy Resources Nonrenewable Energy Resources Nonrenewable energy resources exist Nonrenewable energy resources exist

in limited quantities and, once used, in limited quantities and, once used, cannot be replaced except over cannot be replaced except over millions of years. millions of years.

Nonrenewable resources include fossil Nonrenewable resources include fossil fuels and uranium.fuels and uranium.


Renewable Energy ResourcesRenewable Energy Resources Renewable energy resources are Renewable energy resources are

those that can be replaced in a those that can be replaced in a relatively short period of time (one relatively short period of time (one life span). life span).

Most renewable energy resources Most renewable energy resources originate either directly or indirectly originate either directly or indirectly from the sun. from the sun.


Renewable energy resources includeRenewable energy resources include• hydroelectrichydroelectric• solarsolar• geothermal geothermal • windwind• biomass biomass



Hydroelectric EnergyHydroelectric Energy

Energy obtained from flowing water Energy obtained from flowing water is known as hydroelectric energy. is known as hydroelectric energy.

As the water flows downhill, its PEAs the water flows downhill, its PEgg is is converted into KE. converted into KE.

This kinetic energy can be used to This kinetic energy can be used to turn turbines that are connected to turn turbines that are connected to electric generators. electric generators.




Solar EnergySolar Energy Sunlight that is converted into usable Sunlight that is converted into usable

energy is called solar energy. energy is called solar energy. Passive solar designs use sunlight to Passive solar designs use sunlight to

heat a building heat a building withoutwithout using using machinery. machinery.



In an active solar energy system, In an active solar energy system, sunlight heats collection plates sunlight heats collection plates through which water flows. through which water flows.

Sunlight can also be converted Sunlight can also be converted directly into electrical energy by directly into electrical energy by means of solar cells, or photovoltaic means of solar cells, or photovoltaic cells. cells.

The benefits of solar energy depend The benefits of solar energy depend on the climate. on the climate.




Geothermal EnergyGeothermal Energy

Geothermal energy is thermal energy Geothermal energy is thermal energy beneath Earth’s surface. beneath Earth’s surface.

It is nonpolluting but not widely It is nonpolluting but not widely available. available.



Other Renewable ResourcesOther Renewable Resources

The chemical energy stored in living The chemical energy stored in living things is called biomass energy.things is called biomass energy.

A hydrogen fuel cell generates A hydrogen fuel cell generates electricity by reacting hydrogen and electricity by reacting hydrogen and oxygen. oxygen.


Conserving Energy Resources Conserving Energy Resources

Energy resources can be conserved Energy resources can be conserved by reducing energy needs and by by reducing energy needs and by increasing the efficiency of energy increasing the efficiency of energy use. use.

Finding ways to use less energy or to Finding ways to use less energy or to use energy more efficiently is known use energy more efficiently is known as energy conservation. as energy conservation.

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Chapter 15 Energy. 15.1 Energy and its FormsEnergy 15.1 Energy and its Forms Work is done when a force moves an object through a distance. Energy