Chapter 5: Work, Energy, & Power Section 5.1: Work pages 83 to 86 Section 5.2: Energy Conservation pages 87 to 90 Sections 5.3: Energy Transformations

Chapter 5: Chapter 5: Work, Energy, & Work, Energy, &

PowerPowerSection 5.1: Work pages 83 to 86Section 5.1: Work pages 83 to 86

Section 5.2: Energy Conservation Section 5.2: Energy Conservation

pages 87 to 90pages 87 to 90

Sections 5.3: Energy Transformations Sections 5.3: Energy Transformations

pages 91 to 94pages 91 to 94

Priority Academic Student Skill Priority Academic Student Skill Content Standard 3: Interactions of Energy

and Matter – Energy, such as potential, kinetic, and field, interacts with matter and is transferred during these interactions.

CS 3: 1

All energy can be considered to be either kinetic energy, which is energy of motion, potential energy, which depends on the relative position; or energy contained by a field, such as electromagnetic waves.

Section 5.1: WorkSection 5.1: Work pages 83 to 86 pages 83 to 86

Four subsectionsFour subsections

1.1. What is work? Page 83What is work? Page 83

2.2. Work done by a machine Page 84Work done by a machine Page 84

3.3. Efficiency Page 85Efficiency Page 85

4.4. Power Page 86Power Page 86

5.1: Work: 5.1: Work: What is work?What is work?(2 of 3 parts)(2 of 3 parts)

1.1. The word work The word work means many means many different thingsdifferent things

2.2. What work means in What work means in physicsphysics

The word The word workwork is is used in many different used in many different wayswaysIn physics, work is In physics, work is force times distance. force times distance. W = Fd W = Fd **Work in joules (J) *Work in joules (J) *Force in Newtons (N)Force in Newtons (N)Distance in meters Distance in meters (m)(m)

5.1: Work: 5.1: Work: What is work?What is work?(1 of 3 parts)(1 of 3 parts)

3. Machines do work in 3. Machines do work in the physics sensethe physics sense

When we apply force When we apply force to machines we are to machines we are doing work.doing work.

To be exact, work is To be exact, work is force times distance force times distance moved in the direction moved in the direction of the force.of the force.

United Streaming video: United Streaming video: Work definedWork defined

Chapter 5 Videos\Chapter 5 Videos\Work_Defined.asfWork_Defined.asf

Quiz for page 83: What is work?Quiz for page 83: What is work?

1.1. Define work.Define work.

2.2. If a machine has a constant speed, is If a machine has a constant speed, is work being done? Why or why not?work being done? Why or why not?

3.3. In order to state that work is being done, In order to state that work is being done, work must be done the direction of the work must be done the direction of the _________._________.

4.4. What are the units for each of the What are the units for each of the components of the work equation?components of the work equation?

5.1: Work: Work done by a machine5.1: Work: Work done by a machinepage 84page 84(2 of 3)(2 of 3)

1.1. Work is done Work is done byby forces forces on on objectsobjects

2.2. Units of work *Units of work *

In physics, work is In physics, work is done done byby forces. Work forces. Work is done is done onon the the objects.objects.

Work is measured in Work is measured in joule (J)joule (J) which is which is equal to one newton equal to one newton of force times one of force times one meter of distance.meter of distance.

5.1: Work: Work done by a machine5.1: Work: Work done by a machinepage 84page 84(1 of 3)(1 of 3)

3.3. Input work and output workInput work and output worka.a. Refer to page 84 – Figure 5.3Refer to page 84 – Figure 5.3b.b. Refer to page 84 – Figure 5.4Refer to page 84 – Figure 5.4c.c. The work output of a simple machine can The work output of a simple machine can

never exceed the work input.never exceed the work input.d.d. When you design a machine that When you design a machine that multiplies multiplies force, you pay by having to apply force, you pay by having to apply the force the force over a greater distance.over a greater distance.

5.1: Work: 5.1: Work: EfficiencyEfficiencypage 85 (2 of 4)page 85 (2 of 4)

1.1. What is an What is an efficientefficient machine? * machine? *a.a. All (or most) of the work input All (or most) of the work input

becomes work outputbecomes work outputb.b. Five joules of work input with five Five joules of work input with five

joules of work output.joules of work output.2.2. How friction affects real machinesHow friction affects real machines

In real machines, the work output is In real machines, the work output is always less than the work input due to always less than the work input due to friction and other forces.friction and other forces.

United Streaming video: United Streaming video: World without FrictionWorld without Friction

Chapter 5 Videos\Chapter 5 Videos\A_World_Without_Friction.A_World_Without_Friction.asfasf

5.1: Work: 5.1: Work: EfficiencyEfficiencypage 85 (2 of 4)page 85 (2 of 4)

3.3. The definition of The definition of efficiency *efficiency *

a. The efficiency of a machine is the a. The efficiency of a machine is the ratio of work output to work input i.e. ratio of work output to work input i.e. workwork

output divided by work input times 100output divided by work input times 100.*.*

b. b. Efficiency is usually expressed inEfficiency is usually expressed in

percentpercent. . Refer to page 85.*Refer to page 85.*

4.4. The ideal machineThe ideal machine

The ideal machine would be 100 percent The ideal machine would be 100 percent efficientefficient. Efficiency cannot exceed 100%*. Efficiency cannot exceed 100%*

A most efficient machineA most efficient machinepage 85page 85

BONUS information for use on the BONUS information for use on the content exam chapter 5content exam chapter 5

5.1: Work: 5.1: Work: PowerPowerpage 86 (2 of 3)page 86 (2 of 3)

1.1. How fast the work is doneHow fast the work is done

It makes a difference how fast you do It makes a difference how fast you do work.work.

2.2. What is power? *What is power? *

a. The rate at which work is done is a. The rate at which work is done is called called powerpower..

b. b. Power is work done over timePower is work done over time * *

c. Refer to the example on page 86 *c. Refer to the example on page 86 *

5.1: Work: 5.1: Work: PowerPowerpage 86 (1 of 3)page 86 (1 of 3)

3.3. The units of power *The units of power *

a. Power is measured in Watts (W)a. Power is measured in Watts (W)

b. Work is measured in joules (J)b. Work is measured in joules (J)

c. Time is measured in seconds (s)c. Time is measured in seconds (s)

d. The Watts can also be known as d. The Watts can also be known as

horsepower: one horsepower equalshorsepower: one horsepower equals

746 Watts.746 Watts.

United Streaming video: United Streaming video: define Powerdefine Power

Chapter 5 Videos\Chapter 5 Videos\Power_Defined.asfPower_Defined.asf

5.2: Energy Conservation: 5.2: Energy Conservation: What is energy?What is energy?page 87 (1 of 2)page 87 (1 of 2)

1.1. The definition of energyThe definition of energy a. Energy is the ability to do work. a. Energy is the ability to do work.

b. Any object that has energy has the ability to b. Any object that has energy has the ability to create force.create force.

c. Energy is one of the fundamental buildingc. Energy is one of the fundamental building

blocks of our universe.blocks of our universe.

United Streaming video: United Streaming video: Energy definedEnergy defined

Chapter 5 Videos\Chapter 5 Videos\Energy_Defined.asfEnergy_Defined.asf

5.2: Energy Conservation: 5.2: Energy Conservation: What is energy?What is energy?page 87 (1 of 2)page 87 (1 of 2)

2.2. Units of energyUnits of energy

a. Energy is measured in joules (J)a. Energy is measured in joules (J)

b. Energy is really stored work.b. Energy is really stored work.

c. Any object with energy has the abilityc. Any object with energy has the ability

to use its energy to do work, whichto use its energy to do work, which

means creating a force that acts over ameans creating a force that acts over a

distance.distance.

United Streaming video: United Streaming video: Types of energyTypes of energy

Chapter 5 Videos\Chapter 5 Videos\Types_of_Energy.asfTypes_of_Energy.asf

5.2: Energy Conservation: 5.2: Energy Conservation: Potential energyPotential energypage 88 (2 of 4)page 88 (2 of 4)

1.1. What is potential energy?What is potential energy?a. Comes from the position of an object a. Comes from the position of an object relative to the Earth.relative to the Earth.b. Refer to Figure 5.6 page 88b. Refer to Figure 5.6 page 88

2.2. Where does potential energy come Where does potential energy come from?from?Energy is stored work, so the amount of Energy is stored work, so the amount of energy must be the same amount of energy must be the same amount of work done to lift an object up.work done to lift an object up.


3.3. How to calculate potential energyHow to calculate potential energy

a. Force required to lift an object is thea. Force required to lift an object is the

weight of the object.weight of the object.

b. Work is done to lift the object so theb. Work is done to lift the object so the

equation for work is needed.equation for work is needed.

c. Potential energy is a type of energyc. Potential energy is a type of energy

so the unit is in joules (J)so the unit is in joules (J)

EEpp = m g h = m g h

Potential Energy EquationPotential Energy Equation

EEpp is potential energy in (J) is potential energy in (J)m is mass in kilograms (kg)m is mass in kilograms (kg)g is gravity in 9.8 m/sg is gravity in 9.8 m/s22

h is height that the object was h is height that the object was lifted in meters (m)lifted in meters (m)


4.4. Why is it called potential energy?Why is it called potential energy?

a. Objects that have potential energy do a. Objects that have potential energy do not use their energy until they move. not use their energy until they move.

b. Potential means that something isb. Potential means that something is

capable of becoming active.capable of becoming active.

c. Any object that can move to a lowerc. Any object that can move to a lower

place has the potential to do work onplace has the potential to do work on

the way down, such as a ball down a the way down, such as a ball down a

hill.hill.

5.2: Energy Conservation: 5.2: Energy Conservation: Kinetic energyKinetic energypage 89 (2 of 5)page 89 (2 of 5)

1.1. Kinetic energy is energy of motionKinetic energy is energy of motion

a. Objects also store energy in motion.a. Objects also store energy in motion.

b. Refer to Figure 5.7 page 89b. Refer to Figure 5.7 page 89

2.2. Kinetic energy increases with speedKinetic energy increases with speed

The higher the speed of an object, the The higher the speed of an object, the more energy it has because you have to more energy it has because you have to do work to increase the speed.do work to increase the speed.


3.3. Kinetic energy increases with massKinetic energy increases with mass

Increasing the mass increases the Increasing the mass increases the amount of work you have to do to get an amount of work you have to do to get an object moving, so it also increases the object moving, so it also increases the energy. energy. KINECTICE ENERGY KINECTICE ENERGY DEPENDS ON TWO THINGS: MASS DEPENDS ON TWO THINGS: MASS AND SPEED.AND SPEED.


4.4. The formula for kinetic energyThe formula for kinetic energy

a. Requires work just like potentiala. Requires work just like potential

energyenergy

b. The work has to get the object with ab. The work has to get the object with a

mass (m) from a resting position tomass (m) from a resting position to

speed (v).speed (v).

c. The unit for kinetic energy is the same c. The unit for kinetic energy is the same as the unit for potential energy in as the unit for potential energy in

joules (J)joules (J)

EEkk = ½ mv = ½ mv22

Kinetic Energy EquationKinetic Energy EquationEEkk is the K.E. in joules (j) is the K.E. in joules (j)

m is the mass of object in kilograms m is the mass of object in kilograms (kg)(kg)

VV2 2 is the speed in meters per second is the speed in meters per second squared (m/s)squared (m/s)22


5.5. Kinetic energy increases as the square of Kinetic energy increases as the square of speedspeed

a. This means if you do twice as fast,a. This means if you do twice as fast,

your energy increases by four timesyour energy increases by four times

b. More energy means more force isb. More energy means more force is

needed to stopneeded to stop

c. At a speed of 90 mph you have ninec. At a speed of 90 mph you have nine

times as much energy as you did at times as much energy as you did at 3030

mph.mph.

United Streaming video: United Streaming video: Kinetic and Potential energy Kinetic and Potential energy

defineddefined

Chapter 5 Videos\Chapter 5 Videos\Kinetic_and_Potential_Energy.asfKinetic_and_Potential_Energy.asf

5.2: Energy Conservation: 5.2: Energy Conservation: Conservation of energy*Conservation of energy*

page 90 (1 of 4)page 90 (1 of 4)

1.1. The law of conservation of energy*The law of conservation of energy*

a. Nature never creates or destroysa. Nature never creates or destroys

energy; energy only gets convertedenergy; energy only gets converted

from one form to another.from one form to another.

b. The rule we found for the input andb. The rule we found for the input and

output work of a machine was anoutput work of a machine was an

example of the law of conservation example of the law of conservation ofof

energy.energy.

5.2: Energy Conservation: 5.2: Energy Conservation: Conservation of energyConservation of energy

page 90 (1 of 4)page 90 (1 of 4)

2.2. An example of energy transformationAn example of energy transformation

Read the three paragraphs on page 90Read the three paragraphs on page 90

3.3. The total energy never exceeds the The total energy never exceeds the starting energystarting energy

The energy is divided between potential The energy is divided between potential and kinetic, but the total is unchanged.and kinetic, but the total is unchanged.

United Streaming video: United Streaming video: The law of conservation of The law of conservation of

energyenergy

Chapter 5 Videos\Chapter 5 Videos\The_Law_of_Conservation_of_EnThe_Law_of_Conservation_of_Energy.asfergy.asf

5.2: Energy Conservation: 5.2: Energy Conservation: Conservation of energyConservation of energy

page 90 (1 of 4)page 90 (1 of 4)

4.4. Friction can divert some energyFriction can divert some energy

a. The law of conservation of energy stilla. The law of conservation of energy still

holds true, even when there isholds true, even when there is

friction.friction.

b. The energy converted to heat or wearb. The energy converted to heat or wear

is no longer available to be potential is no longer available to be potential

or kinetic energy, but it was notor kinetic energy, but it was not

destroyed.destroyed.

United Streaming video: United Streaming video: FrictionFriction

Chapter 5 Videos\Chapter 5 Videos\Friction.asfFriction.asf

5.3: Energy Transformations: 5.3: Energy Transformations: Following an energy transformationFollowing an energy transformation

page 91 & 92 (1 of 7)page 91 & 92 (1 of 7)

1.1. The different kinds of energyThe different kinds of energy

a. Kinetic and potential energy are oftena. Kinetic and potential energy are often

called mechanical energy becausecalled mechanical energy because

they involve moving objects.they involve moving objects.

b. There are many other kinds of b. There are many other kinds of

energy, including energy, including radiant energy,radiant energy,

electrical energy, chemical energy, electrical energy, chemical energy, &&

nuclear energy.nuclear energy.


page 91 & 92 (2 of 7)page 91 & 92 (2 of 7)

2.2. An example of energy transformationAn example of energy transformation

Refer to page 91 Figure 5.10Refer to page 91 Figure 5.10

3.3. Chemical energy to potential energyChemical energy to potential energy

a. The chemical potential energy stored ina. The chemical potential energy stored in

the food you ate is converted into the food you ate is converted into simplesimple

sugars.sugars.

b. In climbing the hill, you convert someb. In climbing the hill, you convert some

chemical energy to potential energy.chemical energy to potential energy.


page 91 & 92 (1 of 7)page 91 & 92 (1 of 7)

4.4. Where does “spent” energy go?Where does “spent” energy go?

a. Some of the energy you spent is now a. Some of the energy you spent is now stored as potential energy because stored as potential energy because

youryour

position is higher than when you began.position is higher than when you began.

b. Some of the energy was converted by your b. Some of the energy was converted by your body into heat, chemical changes in body into heat, chemical changes in muscles, and the evaporation of sweat muscles, and the evaporation of sweat from your skin. from your skin.


page 91 & 92 (2 of 7)page 91 & 92 (2 of 7)

5.5. How does potential energy get used?How does potential energy get used?

The increased potential energy is used The increased potential energy is used when converted to kinetic energywhen converted to kinetic energy

6.6. Kinetic energy is used up in the brakesKinetic energy is used up in the brakes

Brakes convert kinetic energy into heat Brakes convert kinetic energy into heat and the wearing away of the brake pads.and the wearing away of the brake pads.


page 91 & 92 (1 of 7)page 91 & 92 (1 of 7)

7.7. The flow of energyThe flow of energy

a. Refer to page 92 Figure 5.12a. Refer to page 92 Figure 5.12

b. During all the energy transformation b. During all the energy transformation

in Figure 5.12, no energy was lostin Figure 5.12, no energy was lost

because energy can never be because energy can never be createdcreated

or destroyed.or destroyed.

5.3: Energy Transformations: 5.3: Energy Transformations: Other forms of energyOther forms of energypage 93 & 94 (2 of 8)page 93 & 94 (2 of 8)

1.1. Energy: nature’s moneyEnergy: nature’s money

Energy is used to buy speed, height, Energy is used to buy speed, height, temperature, mass, and other things which temperature, mass, and other things which diminishes as you use it.diminishes as you use it.

2.2. Mechanical energyMechanical energy

a. Can be either kinetic or potentiala. Can be either kinetic or potential

energyenergy

b. Is form involved in the operation ofb. Is form involved in the operation of

simple machines.simple machines.


3.3. Radiant (meaning light) energyRadiant (meaning light) energya. AKA electromagnetic energya. AKA electromagnetic energyb. Electromagnetic waves includes light we b. Electromagnetic waves includes light we

see, ultraviolet light (UV), X rays, see, ultraviolet light (UV), X rays, infraredinfrared

radiation ( AKA heat), radio waves,radiation ( AKA heat), radio waves, microwaves, and radar.microwaves, and radar.

4.4. Energy from the sunEnergy from the sunRadiant heat from the sun is what keeps the Radiant heat from the sun is what keeps the Earth warm. Earth warm. 1,400 Watts per square meter.1,400 Watts per square meter.


5.5. Electrical energyElectrical energy

6.6. Chemical energyChemical energy

7.7. Nuclear energyNuclear energy

8.8. Thermal energyThermal energy

Documents

Chapter 5: Work, Energy, & Power Section 5.1: Work pages 83 to 86 Section 5.2: Energy Conservation pages 87 to 90 Sections 5.3: Energy Transformations