Chapter 15Chapter 15EnergyEnergy

15.1 Energy and Its 15.1 Energy and Its FormsForms

How are energy and How are energy and work related?work related?

EnergyEnergy is the ability is the ability to do work.to do work.

Energy and Work

Work is a transfer of Work is a transfer of energy.energy.

Work and energy are closely Work and energy are closely related.related.

• Energy is known by the Energy is known by the changes it causes. changes it causes.

• Work is done when a force Work is done when a force moves an object through a moves an object through a distance. Energy is transferred distance. Energy is transferred by a force moving an object by a force moving an object through a distance.through a distance.

• Both work and energy are Both work and energy are typically measured in joules (J).typically measured in joules (J).

What factors does the What factors does the kinetic energy of an kinetic energy of an object depend on?object depend on?

The energy of motion is The energy of motion is called called kinetic energykinetic energy..

Kinetic Energy

depends upon its mass depends upon its mass and speed.and speed.

Doubling the mass in the Doubling the mass in the formula doubles the kinetic formula doubles the kinetic energy.energy.

Doubling the speed quadruples Doubling the speed quadruples the kinetic energy.the kinetic energy.

Kinetic Energy

Calculating Kinetic EnergyCalculating Kinetic Energy

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

Kinetic Energy

Calculating Kinetic EnergyCalculating Kinetic Energy

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

KE = KE = .10 x 8.10 x 822 = = 6.46.4 = = 3.23.2 2 22 2

Kinetic Energy

2. 2. A 1400-kilogram car A 1400-kilogram car is moving at a speed of is moving at a speed of 25 m/s. How much 25 m/s. How much kinetic energy does the kinetic energy does the car have? car have?

Kinetic Energy

3. 3. A 50.0-kilogram A 50.0-kilogram cheetah has a kinetic cheetah has a kinetic energy of 18,000 J. How energy of 18,000 J. How fast is the cheetah fast is the cheetah running? (running? (Hint: Hint: Rearrange the equation Rearrange the equation to solve for to solve for v.v.) )

Kinetic Energy

KE PracticeKE Practice

1.1. Calculate KE of a 1500 kg Calculate KE of a 1500 kg car moving at 29 m/scar moving at 29 m/s

2.2. If you use the sun as your If you use the sun as your frame of reference, you frame of reference, you always have kinetic energy. always have kinetic energy. Why? Why?

How is gravitational How is gravitational potential energy determined?potential energy determined?

Potential energyPotential energy is energy is energy that is stored as a result of that is stored as a result of position or shape. position or shape.

Potential Energy

using its mass, its using its mass, its height, and the height, and the acceleration due to acceleration due to gravity.gravity.

Gravitational Potential Gravitational Potential EnergyEnergy

Potential energy that Potential energy that depends upon an object’s depends upon an object’s height is called height is called gravitational gravitational potential energypotential energy. .

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

Potential Energy

The unit for mass is kilograms.The unit for mass is kilograms.The unit for height is meters.The unit for height is meters.Acceleration due to gravity, Acceleration due to gravity, gg, , has a value in SI units of 9.8 has a value in SI units of 9.8 m/s2 on Earth.m/s2 on Earth.

The unit for gravitational The unit for gravitational potential energy is joules.potential energy is joules.

Potential Energy

Doubling either the mass of Doubling either the mass of the object or its height the object or its height doubles its gravitational doubles its gravitational potential energy.potential energy.

Potential Energy

What is the potential energy What is the potential energy relative to the water surface relative to the water surface of a diver at the top of a 10.0-of a diver at the top of a 10.0-meter-high diving platform. meter-high diving platform. Suppose she has a mass of Suppose she has a mass of 50.0 kilograms.50.0 kilograms.

Potential Energy

GPE ExampleGPE ExampleA 65 kg rock climber A 65 kg rock climber

ascends a cliff. What is ascends a cliff. What is the climber’s GPE at a the climber’s GPE at a point 35 m above the base point 35 m above the base of the cliff?of the cliff?

GPE PracticeGPE Practice

1. A car with a mass of 1200 1. A car with a mass of 1200 kg at the top of a 42 m hillkg at the top of a 42 m hill

2. A 65 kg climber on top of 2. A 65 kg climber on top of Mount Everest (8800 m Mount Everest (8800 m high)high)

3. A 0.52 kg bird flying at an 3. A 0.52 kg bird flying at an altitude of 550 maltitude of 550 m

Elastic Potential EnergyElastic Potential Energy

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

Something that is elastic Something that is elastic springs back to its original springs back to its original shape after it is stretched or shape after it is stretched or compressed. compressed.

Potential Energy

What are the major forms What are the major forms of energy?of energy?

Forms of Energy

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

All energy can be considered to All energy can be considered to be one of three forms:be one of three forms:

• kinetic energy,kinetic energy,• potential energy, andpotential energy, and• energy in fields such as those energy in fields such as those produced by electromagnetic produced by electromagnetic waves. waves.

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

Mechanical EnergyMechanical Energy

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

Mechanical energy is the sum Mechanical energy is the sum of an object’s potential of an object’s potential energy and kinetic energy. energy and kinetic energy.

Forms of Energy

Thermal (Heat) EnergyThermal (Heat) Energy

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

When an object’s atoms move When an object’s atoms move faster, its thermal energy faster, its thermal energy increases, and the object increases, and the object becomes warmer.becomes warmer.

Forms of Energy

Chemical EnergyChemical Energy

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

When bonds are broken, the When bonds are broken, the released energy can do work. released energy can do work. All chemical compounds, All chemical compounds, including fuels such as coal including fuels such as coal and gasoline, store energy.and gasoline, store energy.

Forms of Energy

Electrical EnergyElectrical Energy

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

Electric charges can exert Electric charges can exert forces that do work.forces that do work.

Forms of Energy

Electromagnetic EnergyElectromagnetic Energy

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

Visible light and X-rays are Visible light and X-rays are examples of electromagnetic examples of electromagnetic energy. energy.

Forms of Energy

Nuclear EnergyNuclear Energy

The nucleus of an atom is held The nucleus of an atom is held together by strong and weak together by strong and weak nuclear forces, which can store nuclear forces, which can store an enormous amount of an enormous amount of potential energy. potential energy.

• The energy stored in atomic The energy stored in atomic nuclei is known as nuclei is known as nuclear nuclear energyenergy. .

• Nuclear fissionNuclear fission (splitting (splitting nuclei) nuclei)

• Nuclear fusionNuclear fusion (nuclei (nuclei combine to form a more combine to form a more massive nucleus) massive nucleus)

Forms of Energy

Assessment Questions

1.1. How are work and energy How are work and energy related? related?

a.a. Energy is the rate of Energy is the rate of doing work.doing work.

b.b. Work is a form of energy.Work is a form of energy.

c.c. Work is the transfer of Work is the transfer of energy.energy.

d.d. Energy is created by work.Energy is created by work.

Assessment Questions

2.2. A moving object with a A moving object with a mass of 10 kg has 320 J of mass of 10 kg has 320 J of kinetic energy due to its kinetic energy due to its motion. How fast is the motion. How fast is the object moving?object moving?a.a. 64 m/s64 m/sb.b. 32 m/s32 m/sc.c. 8 m/s8 m/sd.d. 10 m/s10 m/s

Assessment Questions

3.3. Which of these is an Which of these is an example of elastic potential example of elastic potential energy?energy?

a.a. a bow prepared to release a bow prepared to release an arrowan arrow

b.b. a rubber ball thrown into a rubber ball thrown into the airthe air

c.c. a book about to fall from a book about to fall from a tablea table

d.d. a truck pulling a trailera truck pulling a trailer

Assessment Questions4.4. A small airplane and a helicopter A small airplane and a helicopter

have identical masses. If the have identical masses. If the airplane’s altitude compared to airplane’s altitude compared to the ground is three times that of the ground is three times that of the helicopter, how much more the helicopter, how much more gravitational potential energy gravitational potential energy does the airplane have than the does the airplane have than the helicopter? helicopter? a.a. 0.333 times as much0.333 times as muchb.b. 3 times as much3 times as muchc.c. 6 times as much6 times as muchd.d. 9 times as much9 times as much

Assessment Questions

5.5. The energy stored in the The energy stored in the bonds between atoms of a bonds between atoms of a compound is called compound is called

a.a. electromagnetic energy.electromagnetic energy.

b.b. chemical energy.chemical energy.

c.c. atomic energy.atomic energy.d.d. thermal energy.thermal energy.

Chapter 15Chapter 15EnergyEnergy

15.2 Energy 15.2 Energy Conversion and Conversion and ConservationConservation

Explain the energy Explain the energy conversions in:conversions in:A) a pendulumA) a pendulumB) pole vaultsB) pole vaults

Energy Conversion

Energy can be Energy can be converted from one converted from one form to another. form to another.

Conservation of Energy

What is the law of What is the law of conservation of energy?conservation of energy?

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

Energy Conversions

What energy conversion What energy conversion takes place as an object falls takes place as an object falls toward Earth?toward Earth?

The gravitational The gravitational potential energy of an potential energy of an object is converted to the object is converted to the kinetic energy of motion kinetic energy of motion as the object falls.as the object falls.

Energy Conversion in PendulumsEnergy Conversion in Pendulums

A pendulum consists of a weight A pendulum consists of a weight swinging back and forth from a rope swinging back and forth from a rope or string. or string.

Energy Conversions

Energy Energy TransformationsTransformations

Flight of a ballFlight of a ball

Energy TransformationsEnergy TransformationsBouncing ballBouncing ball

Energy Conversion CalculationsEnergy Conversion Calculations

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

Mechanical energy = KE + Mechanical energy = KE + PEPE

Energy Conversions

The law of conservation of The law of conservation of energy applies to any energy applies to any mechanical process. If mechanical process. If friction can be neglected, the friction can be neglected, the total mechanical energy total mechanical energy remains constant. remains constant.

Energy Conversions

Conservation of Mechanical Conservation of Mechanical EnergyEnergy

At a construction site, a 1.50-kg At a construction site, a 1.50-kg brick is dropped from rest and brick is dropped from rest and hits the ground at a speed of hits the ground at a speed of 26.0 m/s. Assuming air 26.0 m/s. Assuming air resistance can be ignored, resistance can be ignored, calculate the gravitational calculate the gravitational potential energy of the brick potential energy of the brick before it was dropped.before it was dropped.

Energy Conversions

1. 1. A 10-kg rock is dropped A 10-kg rock is dropped and hits the ground below at and hits the ground below at a speed of 60 m/s. Calculate a speed of 60 m/s. Calculate the gravitational potential the gravitational potential energy of the rock before it energy of the rock before it was dropped. You can ignore was dropped. You can ignore the effects of friction.the effects of friction.

Energy Conversions

Conversions Conversions ReviewReview

1.1. Describe conversions Describe conversions between potential and between potential and kinetic as a tennis ball kinetic as a tennis ball drops, hits the ground, and drops, hits the ground, and bounces back up.bounces back up.

2.2. What energy conservations What energy conservations take place in a pendulum? take place in a pendulum? Why does it eventually Why does it eventually stop?stop?

Conversions Conversions ReviewReview

3. Describe the energy 3. Describe the energy conversions that take place conversions that take place when a flashlight is turned on.when a flashlight is turned on.

4. Identify the conversions: An 4. Identify the conversions: An object is raised and then object is raised and then allowed to fall. As it hits the allowed to fall. As it hits the ground it stops, produces a ground it stops, produces a sound, and becomes warmer.sound, and becomes warmer.

Energy and Mass

How are energy and mass How are energy and mass related?related?

Einstein’s equation, Einstein’s equation, E E = = mcmc22, , says that energy and mass says that energy and mass are equivalent and can be are equivalent and can be converted into each other.converted into each other.

Albert Einstein developed his Albert Einstein developed his special theory of relativity in 1905. special theory of relativity in 1905. This theory included the now-This theory included the now-famous equation famous equation E E = = mcmc22..

• E E is energy, is energy, m m is mass, and is mass, and c c is is the speed of light. the speed of light.

• The speed of light is an The speed of light is an extremely large number, 3.0 × extremely large number, 3.0 × 101088 meters per second. meters per second.

• A tiny amount of matter can A tiny amount of matter can produce an enormous amount of produce an enormous amount of energy.energy.

Energy and Mass

Suppose 1 gram of matter were Suppose 1 gram of matter were entirely converted into energy.entirely converted into energy.

Energy and Mass

In nuclear fission and fusion In nuclear fission and fusion reactions, however, large reactions, however, large amounts of energy are released amounts of energy are released by the destruction of very small by the destruction of very small amounts of matter. amounts of matter.

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

Energy and Mass

Assessment Questions

1.1. What energy conversion What energy conversion occurs as a result of friction? occurs as a result of friction?

a.a. chemical energy to thermal chemical energy to thermal energyenergy

b.b. kinetic energy to potential kinetic energy to potential energyenergy

c.c. kinetic energy to thermal kinetic energy to thermal energyenergy

d.d. potential energy to thermal potential energy to thermal energyenergy

Assessment Questions

2.2. At what point in a pendulum’s At what point in a pendulum’s swing does it have maximum swing does it have maximum kinetic energy?kinetic energy?a.a. the highest point of the the highest point of the

swingswingb.b. the lowest point of the swingthe lowest point of the swingc.c. halfway between the lowest halfway between the lowest

and highest pointand highest pointd.d. same at all positions of the same at all positions of the

swingswing

Assessment Questions

3.3.According to the law of According to the law of conservation of mass, energy conservation of mass, energy can be converted from one can be converted from one from to another but not from to another but not created or destroyed.created or destroyed.

TrueTrueFalseFalse