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Unit 4, Chapter

c enceFoundations ofPhysics

Chapter 9Chapter 9

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p

Unit 4: Energy and Momentum

10.1 Machines and MechanicalAdvantage

10.2 Work 10.3 Energy and onservation o! Energy

ha"ter 10 Work and Energy

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ha"ter 10 #$%ectives1. alculate the mechanical advantage !or a

lever or ro"e and "ulleys.

2. alculate the &ork done in %oules !orsituations involving !orce and distance.

3. 'ive e(am"les o! energy and trans!ormationo! energy !rom one !orm to another.

4. alculate "otential and kinetic energy.

). A""ly the la& o! energy conservation tosystems involving "otential and kineticenergy.

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ha"ter 10 *oca$ulary +ermsmachineenergyin"ut !orce

out"ut !orcethermal energyram"gearscre&ro"e and"ulleysclosed system&ork

lever!rictionmechanical

systemsim"le machine"otential energykinetic energyradiant energynuclear energychemical energymechanicalenergy

mechanicaladvantage

%oule"ressureenergyconservation o!energyelectrical energy

in"ut out"utin"ut armout"utarm!ulcrum

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10.1 Machines and MechanicalAdvantage,ey -uestion:

How do simplemachines work?

/tudents read /ection10.1 A +E

nvestigation 10.1

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10.1 Machines The ability of humans to buildbuildings and move mountainsbegan with our invention ofmachines .

In physics the term simplemachine means a machinethat uses only the forcesdirectly applied andaccomplishes its task with asingle motion.

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10.1 Machines The best way to analyze what a machinedoes is to think about the machine in termsof input and output .

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10.1 Mechanical AdvantageMechanical advantage is theratio o! out"ut !orce to in"ut!orce.

or a ty"ical automotive %ackthe mechanical advantage is 30or more.A !orce o! 100 ne&tons 22.)"ounds a""lied to the in"utarm o! the %ack "roduces anout"ut !orce o! 35000 ne&tons67) "ounds 8 enough to li!tone corner o! an automo$ile.

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10.1 Mechanical Advantage

MA 9o

i

#ut"ut !orce

n"ut !orce

Mechanical

advantage

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10.1 Mechanical Advantage o! a;ever

MA lever 9 ; i ; o

;ength o! in"ut armm

;ength o! out"ut arm

m

Mechanical

advantage

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10.1 alculate "ositionWhere should the !ulcrum o! alever $e "laced so one "erson&eighing 700 can li!t the edge

o! a stone $lock &ith a mass o!)00 kgo? ismade $et&een tor=ue androtation s"eed .

An out"ut gear &ill turn&ith more tor=ue &hen itrotates slo&er than thein"ut gear.

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10.1 am"s and /cre&sam"s reduce in"ut !orce$y increasing the distance

over &hich the in"ut !orceneeds to act.A scre& is a sim"le machinethat turns rotating motion

into linear motion.A thread &ra"s around ascre& at an angle5 like theangle o! a ram".

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10.2 Work ,ey -uestion:hat are the

conse!uences ofmultiplying forces inmachines?

/tudents read /ection 10.2 A +Envesti ation 10.2

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10.2 Work n "hysics5 &ork has a very s"eci@c

meaning.

n "hysics5 &orkre"resents ameasura$le changein a system5caused $y a !orce.

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10.2 Work If you push a bo" with a force of onenewton for a distance of one meter # youhave done e"actly one $oule of work.

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10.2 Work !orce is "arallel todistance

W 9 ( distance m

orce

Work %oules

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10.2 Work !orce at angle todistance

W 9 d cos

istance m

orce

Work %oules Angle

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10.2 Work done against gravity

W 9mgh

Beight o$%ect raised m

'ravity mCsec 2

Work %oules

Mass g

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10.3 Why the "ath doesnDtmatter

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10.3 alculate &ork A crane li!ts a steel $eam&ith a mass o! 15)00 kg.

alculate ho& much &orkis done against gravity i!the $eam is li!ted )0meters in the air.

Bo& much time does ittake to li!t the $eam i!the motor o! the cranecan do 105000 %oules o!&ork "er second

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10.3 Energy and onservation o!Energy Energy is the a$ility to make thingschange.A system that has energy has thea$ility to do &ork.Energy is measured in the same unitsas &ork $ecause energy is trans!erred

during the action o! &ork.

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10.3 orms o! EnergyMechanical energy is the energy "ossessed$y an o$%ect due to its motion or its"osition.adiant energy includes light5 micro&aves5radio &aves5 (>rays5 and other !orms o!electromagnetic &aves.uclear energy is released &hen heavyatoms in matter are s"lit u" or light atomsare "ut together.+he electrical energy &e use is derived !romother sources o! energy.

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10.3 otential Energy

E " 9 mgh Beight m

Mass kg

otential Energ y %oules

Accelerationo! gravity mCsec 2

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10.3 otential EnergyA cart &ith a mass o! 102 kgis "ushed u" a ram".

+he to" o! the ram" is 4meters higher than the$ottom.

Bo& much "otential energy

is gained $y the cart

it take to get u" the ram"<

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10.3 ,inetic EnergyEnergy o! motion is called kinetic energy .

+he kinetic energy o! a moving o$%ect

de"ends on t&o things: mass and s"eed.,inetic energy is "ro"ortional to mass.

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10.3 ,inetic Energy%athematically# kinetic energy increases asthe s!uare of speed.

If the speed of an ob$ect doubles# its kineticenergy increases four times. &mass is constant'

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10.3 ,inetic Energy

E k 9 1mv 2

2

/"eed mCsec

Mass kg

,inetic Energy%oules

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10.3 ,inetic Energy,inetic energy $ecomes im"ortant incalculating $raking distance.

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10.3 alculate ,inetic EnergyA car &ith a mass o!15300 kg is going straightahead at a s"eed o! 30

mCsec 67 m"h .+he $rakes can su""ly a!orce o! F5)00 .alculate:

a +he kinetic energy o!the car.$ +he distance it takes

to sto".

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10.3 ;a& o! onservation o!EnergyAs energy takes di?erent !orms and changes things $y doing &ork5 nature kee"s "er!ecttrack o! the total.

o ne& energy is created and no e(isting energy is destroyed.

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10.3 Energy and onservation o!Energy

,ey -uestion:

How is motion on atrack related toenergy?

/tudents read /ection10.3 GE # E

nvestigation 10.3

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A""lication: Bydroelectrico&er