chapter 15: energy. standard sps7. students will relate transformations and flow of energy within a...

Chapter 15: EnergyChapter 15: Energy

StandardStandard

SPS7. Students will relate SPS7. Students will relate transformations and flow of energy transformations and flow of energy within a systemwithin a system– Identify energy transformations within a Identify energy transformations within a

system (e.g. lighting of a match).system (e.g. lighting of a match).

Section 15.1: Energy and Its Section 15.1: Energy and Its FormsForms

EnergyEnergy is the ability to do is the ability to do workwork or or supply supply heatheat..

When When workwork is done on an object, the is done on an object, the energyenergy is is transferredtransferred to that object. to that object.

Both Both workwork and and energyenergy are measured are measured in in Joules (J).Joules (J).

EnergyEnergy

Many forms of Many forms of energyenergy can be can be classified into two general types: classified into two general types: kinetic energy and potential energykinetic energy and potential energy..

Kinetic EnergyKinetic Energy

Kinetic energyKinetic energy is the energy of is the energy of motionmotion..

Formula for kinetic energyFormula for kinetic energy

KE = ½ mvKE = ½ mv22

KE = kinetic energy (J)KE = kinetic energy (J)

m = mass (kg)m = mass (kg)

v = velocity (m/s)v = velocity (m/s)

Kinetic EnergyKinetic Energy Notice that Notice that doublingdoubling the the massmass would would

doubledouble the the kinetic energykinetic energy.. However, However, doublingdoubling the the speedspeed would would

quadruplequadruple the the kinetic energykinetic energy..KE = ½ mvKE = ½ mv22

½ (50kg)(10m/s)½ (50kg)(10m/s)22 = 2500J = 2500J½ (½ (100kg100kg)(10m/s))(10m/s)22 = 5000J (double) = 5000J (double)½(50kg)(½(50kg)(20m/s20m/s))22 = 10000J = 10000J (quadruple)(quadruple)

Remember: 1 kgRemember: 1 kg..mm22/s/s22 = 1J = 1J

Practice ProblemsPractice Problems

A 0.10kg bird is flying at a constant A 0.10kg bird is flying at a constant speed of 8.0m/s. What is the bird’s speed of 8.0m/s. What is the bird’s kinetic energy?kinetic energy?

A 70.0kg man is walking at a speed of A 70.0kg man is walking at a speed of 2.0m/s. What is his kinetic energy?2.0m/s. What is his kinetic energy?

A 50.0kg cheetah has a kinetic energy A 50.0kg cheetah has a kinetic energy of 18,000J. How fast is the cheetah of 18,000J. How fast is the cheetah running?running?

Practice ProblemsPractice Problems

A 0.10kg bird is flying at a constant speed of A 0.10kg bird is flying at a constant speed of 8.0m/s. What is the bird’s kinetic energy?8.0m/s. What is the bird’s kinetic energy?

½ (0.10kg)(8.0m/s)½ (0.10kg)(8.0m/s)22 = 3.2J = 3.2J A 70.0kg man is walking at a speed of A 70.0kg man is walking at a speed of

2.0m/s. What is his kinetic energy?2.0m/s. What is his kinetic energy?

½ (70.0kg)(2.0m/s)½ (70.0kg)(2.0m/s)22 = 140J = 140J A 50.0kg cheetah has a kinetic energy of A 50.0kg cheetah has a kinetic energy of

18,000J. How fast is the cheetah running?18,000J. How fast is the cheetah running?

Square root [2(18,000kgSquare root [2(18,000kg..mm22/s/s22)/50.0kg] = )/50.0kg] = 27m/s27m/s

Potential EnergyPotential Energy

Potential EnergyPotential Energy is energy that is is energy that is storedstored as a result of as a result of positionposition or shape. or shape.

Ex: Lifting a book increases its Ex: Lifting a book increases its stored stored energyenergy, but letting the book go turns , but letting the book go turns the energy into the energy into kinetic energykinetic energy..

Two forms of potential energy are Two forms of potential energy are gravitational potential energygravitational potential energy and and elastic potential energyelastic potential energy..

Gravitational Potential Gravitational Potential EnergyEnergy

Potential energy that depends on an Potential energy that depends on an object’s object’s heightheight is called is called gravitational gravitational potential energypotential energy..

This type of potential energy This type of potential energy increasesincreases when an object is raised to when an object is raised to a a higherhigher level. level.


Formula for potential energyFormula for potential energy

PE = mghPE = mgh

PE = potential energy (J)PE = potential energy (J)m = mass (kg)m = mass (kg)g = acceleration due to gravity (9.8 g = acceleration due to gravity (9.8

m/sm/s22))h = height (m)h = height (m)


Notice that Notice that doublingdoubling either the either the massmass of of the object or its the object or its heightheight doubles its doubles its gravitational potential energygravitational potential energy..

PE = mghPE = mgh

(50kg)(9.8m/s(50kg)(9.8m/s22)(10m) = 4900J)(10m) = 4900J

((100kg100kg)(9.8m/s)(9.8m/s22)(10m) = 9800J )(10m) = 9800J (double)(double)

(50kg)(9.8m/s(50kg)(9.8m/s22)()(20m20m) = 9800J (double)) = 9800J (double)

Elastic Potential EnergyElastic Potential Energy

The potential energy of an object The potential energy of an object that is that is stretched or compressedstretched or compressed is is known as known as elastic potential energyelastic potential energy..

Forms of EnergyForms of Energy

The major forms of energy are The major forms of energy are mechanical energy, thermal energy, mechanical energy, thermal energy, chemical energy, electrical energy, chemical energy, electrical energy, electromagnetic energy, and nuclear electromagnetic energy, and nuclear energyenergy..

Each form of energy can be Each form of energy can be convertedconverted into other forms of energy. into other forms of energy.

Mechanical EnergyMechanical Energy

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

Mechanical energy is the Mechanical energy is the sumsum of an of an object’s object’s kinetickinetic and and potentialpotential energy. energy.

Thermal EnergyThermal Energy

The The totaltotal potential and kinetic energy potential and kinetic energy of all the of all the microscopic particlesmicroscopic particles in an in an object make up its object make up its thermal energythermal energy..

When an object’s atoms move When an object’s atoms move fasterfaster, , its thermal energy its thermal energy increasesincreases and the and the object becomes object becomes warmerwarmer..

Chemical EnergyChemical Energy

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

When bonds are When bonds are brokenbroken, the released , the released energy can do energy can do workwork..

Electrical EnergyElectrical Energy

Electrical energyElectrical energy is the energy is the energy associated with associated with electric chargeselectric charges..

Electromagnetic EnergyElectromagnetic Energy

Electromagnetic energyElectromagnetic energy is a form of is a form of energy that travels through energy that travels through spacespace in in the form of the form of waveswaves..

Nuclear EnergyNuclear Energy

The energy stored in The energy stored in atomic nucleiatomic nuclei is is known as known as nuclear energynuclear energy..

Section 15.1 AssessmentSection 15.1 Assessment

Describe the relationship between Describe the relationship between work and energy.work and energy.

How is the kinetic energy of an object How is the kinetic energy of an object determined?determined?

What factors determine the What factors determine the gravitational potential energy of an gravitational potential energy of an object?object?

When you heat a pot of water over a When you heat a pot of water over a flame, what form of energy is added to flame, what form of energy is added to the water? the water?


What kind of energy is represented by What kind of energy is represented by an archer stretching a bow string?an archer stretching a bow string?

Can an object have both kinetic Can an object have both kinetic energy and potential energy at the energy and potential energy at the same time?same time?

A 60.0kg person walks from the A 60.0kg person walks from the ground to the roof of a 74.8m tall ground to the roof of a 74.8m tall building. How much gravitational building. How much gravitational potential energy does she have?potential energy does she have?(60.0kg)(9.8m/s(60.0kg)(9.8m/s22)(74.8m) = 44,000J)(74.8m) = 44,000J

Section 15.2: Energy Section 15.2: Energy Conversion and ConservationConversion and Conservation

EnergyEnergy can be can be convertedconverted from one from one form to another.form to another.

The process of changing The process of changing energyenergy from from one form to another is one form to another is energy energy conversionconversion..

Ex: Ex: Light bulbsLight bulbs convert convert electrical electrical energyenergy into into thermal energythermal energy and and electromagnetic energy.electromagnetic energy.

Conservation of EnergyConservation of Energy

The The law of conservation of energylaw of conservation of energy states that energy cannot be states that energy cannot be createdcreated or or destroyeddestroyed..

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

Energy ConversionsEnergy Conversions

The The gravitational potential energygravitational potential energy of an of an object is converted to the object is converted to the kinetic kinetic energyenergy of motion as the object of motion as the object fallsfalls..

A A pendulumpendulum consists of a consists of a weightweight swinging back and forth from a rope or swinging back and forth from a rope or string.string.

Kinetic energyKinetic energy undergoes undergoes

constant conversion as aconstant conversion as a

pendulumpendulum swings. swings.

Energy ConversionsEnergy Conversions

When When frictionfriction is small enough to be is small enough to be ignored, the total mechanical energy ignored, the total mechanical energy remains remains constantconstant..

Formula for conversion of mechanical Formula for conversion of mechanical energyenergy

(KE + PE)(KE + PE)11 = (KE + PE) = (KE + PE)22

Sample ProblemSample Problem At a construction site, a 1.50kg brick At a construction site, a 1.50kg brick

is dropped from rest and hits the is dropped from rest and hits the ground at a speed of 26.0m/s. ground at a speed of 26.0m/s. Calculate the gravitational potential Calculate the gravitational potential energy of the brick before it was energy of the brick before it was dropped.dropped.

(KE + PE)(KE + PE)11 = (KE + PE) = (KE + PE)22

KEKE11 = 0J = 0J 0J + PE0J + PE11 = KE = KE2 2 + 0J+ 0J

PEPE11 = ? = ? KEKE22 = ½ mv = ½ mv22

KEKE22 = ½ mv = ½ mv22 PEPE11 = ½ = ½ (1.50kg)(26.0m/s)(1.50kg)(26.0m/s)22

PEPE22 = 0J = 0J PEPE11 = 507J = 507J

Practice ProblemsPractice Problems A 10kg rock is dropped and hits the A 10kg rock is dropped and hits the

ground below at a speed of 60m/s. ground below at a speed of 60m/s. Calculate the gravitational potential Calculate the gravitational potential energy of the rock before you energy of the rock before you dropped it.dropped it.

A pendulum with a 1.0kg weight is set A pendulum with a 1.0kg weight is set in motion from a position of 0.40m in motion from a position of 0.40m above the lowest point on the path of above the lowest point on the path of the weight. What is the kinetic energy the weight. What is the kinetic energy of the pendulum at the lowest point?of the pendulum at the lowest point?

0J + PE0J + PE11 = KE = KE22 + 0J PE + 0J PE11 = ½ (10kg)(60m/s) = ½ (10kg)(60m/s)22 = 18000J = 18000J

0J + PE0J + PE11 = KE = KE22 + 0J + 0JKEKE22 = mgh = 1.0kg x 9.8m/s = mgh = 1.0kg x 9.8m/s22 x 0.40m = 4J x 0.40m = 4J

Energy and MassEnergy and Mass

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

In other words, In other words, energyenergy is released as is released as matter is matter is destroyeddestroyed, and , and mattermatter can can be be createdcreated from energy. from energy.

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


What does the law of conservation of What does the law of conservation of energy state?energy state?

As an object falls in free fall, what As an object falls in free fall, what energy change is taking place?energy change is taking place?

What did Einstein conclude about the What did Einstein conclude about the relationship between mass and relationship between mass and energy?energy?

What type of energy change results What type of energy change results when friction slows down an object?when friction slows down an object?


Describe the energy of a playground Describe the energy of a playground swing at its highest position.swing at its highest position.

A 0.15kg ball is thrown into the air A 0.15kg ball is thrown into the air and rises to a height of 20.0m. How and rises to a height of 20.0m. How much kinetic energy did the ball much kinetic energy did the ball initially have?initially have?

0J + KE0J + KE11 = PE = PE22 + 0J + 0JKEKE11 = mgh = 0.15kg x 9.8m/s = mgh = 0.15kg x 9.8m/s22 x 20.0m = 29J x 20.0m = 29J

Section 15.3: Energy Section 15.3: Energy ResourcesResources

Nonrenewable energy resourcesNonrenewable energy resources exist in limited quantities and cannot exist in limited quantities and cannot be replaced except over the course be replaced except over the course of of millions of yearsmillions of years..

Nonrenewable energy resources Nonrenewable energy resources include include oil, natural gas, coal, and oil, natural gas, coal, and uraniumuranium..

Fossil FuelsFossil Fuels Oil, natural gas, and coal are known Oil, natural gas, and coal are known

as as fossil fuelsfossil fuels because they were because they were formed underground from the formed underground from the remainsremains of once-living of once-living organismsorganisms..

Fossil fuels are relatively Fossil fuels are relatively inexpensiveinexpensive and are usually readily available, but and are usually readily available, but their use creates their use creates pollutionpollution..

Renewable Energy Renewable Energy ResourcesResources

Renewable energy resourcesRenewable energy resources are are resources that can be replaced in a resources that can be replaced in a relatively relatively shortshort period of time. period of time.

Renewable energy resources include Renewable energy resources include hydroelectric, solar, geothermal, hydroelectric, solar, geothermal, wind, biomass, and, in the future, wind, biomass, and, in the future, nuclear fusionnuclear fusion..

Hydroelectric EnergyHydroelectric Energy Energy obtained from Energy obtained from flowing waterflowing water

is known as is known as hydroelectric energyhydroelectric energy.. As water flows downhill its As water flows downhill its kinetic kinetic

energyenergy can be used to turn can be used to turn turbinesturbines that are connected to that are connected to electricelectricgeneratorsgenerators..

The downside is that The downside is that damsdams prohibit prohibit fishfish from from swimming upstream toswimming upstream tospawnspawn..

Solar EnergySolar Energy

SunlightSunlight that is converted into usable that is converted into usable energy is called energy is called solar energysolar energy..

Sunlight can be converted directly Sunlight can be converted directly into electrical energy by into electrical energy by solarsolarcells (photovoltaic cells).cells (photovoltaic cells).

Solar energy is Solar energy is nonpollutingnonpolluting,,but for areas where but for areas where cloudy dayscloudy days are frequent, are frequent, solar energy is less solar energy is less practicalpractical..

Geothermal EnergyGeothermal Energy

Geothermal energyGeothermal energy is thermal energy is thermal energy beneath the beneath the Earth’s surfaceEarth’s surface..

Geothermal energy is Geothermal energy is nonpollutingnonpolluting, , but is not but is not widely availablewidely available..

Biomass EnergyBiomass Energy

The chemical energy stored in The chemical energy stored in living living thingsthings is called is called biomass energybiomass energy..

Many people around the world burn Many people around the world burn woodwood to heat their to heat their homeshomes or for or for cookingcooking..

Hydrogen Fuel CellHydrogen Fuel Cell

A A hydrogen fuel cellhydrogen fuel cell generates generates electricity by reacting electricity by reacting hydrogen with hydrogen with oxygenoxygen..

The end product of fuel cells is The end product of fuel cells is waterwater, , so they are so they are nonpollutingnonpolluting..

Conserving Energy Conserving Energy ResourcesResources

Energy resources can be Energy resources can be conservedconserved by by reducingreducing energy needs and by energy needs and by increasing the increasing the efficiencyefficiency of energy of energy use.use.

Finding ways to use Finding ways to use less energyless energy or to or to use energy more use energy more efficientlyefficiently is known is known as as energy conservationenergy conservation..


List the major nonrenewable and List the major nonrenewable and renewable sources of energy.renewable sources of energy.

What could be done to make present What could be done to make present energy resources last longer?energy resources last longer?

Why are coal, oil, and natural gas Why are coal, oil, and natural gas called fossil fuels?called fossil fuels?