Lab12:EnergyConversions

Purpose

Tomeasuretheconversionofenergybetweenpotentialandkineticusingan inclinedplane

Background

Knowinghowenergybehavesisevenmoreimportantthanknowingwhatitis. Thelawofenergyconservationstatesthatenergycannotbeeithercreatedor destroyed.Sotheenergyofasystemmustremainthesamebeforeandafter thingshappentoit.Apersonwalkingtothetopofaburningbuildinghasto worktoclimbthestairs.Theenergyfromtheworkisthenstoredinpotential form becauseoftheforce ofgravitypullingherdown.Ifshewere tojump from theburningbuildingontoafirefighters’trampoline,herpotentialenergy wouldbeconvertedintokineticenergyasshewasfalling. Asshespeedsup whilefalling,herpotentialenergydecreasesbecausesheiscloser totheground andherkineticenergyincreasesasherspeedincreases.Whenshehitsthe trampolineshewillslowdownandherenergywillconvertintovibrations (elasticpotentialenergy),heatandnoise.

SkillsFocus

Makinggeneralizations,interpretingdata,applyingconcepts,drawing conclusions

Procedure

1. StartVirtualPhysicsandselectEnergyConversionsfromthelistof assignments. ThelabwillopenintheMechanicslaboratory.

2. Thelaboratorywillbe setupwitharamp,aballon theramp,andaplunger ontheball.UsingtheForcebuttontohittheplunger,youwillpushtheball uptheramp.Theballwillstopatsomepointandcomerollingbackdown theramp.

3. Youwillneedtorecordandusethedatafromtheexperiment.Clickonthe LabBooktoopenit.Theclickthe redRecordingbutton. WhentheForcebutton isclicked,thedataselectedwiththecheckmarkswillbeautomatically recorded.

4. ClicktheForcebuttontohittheballuptheramp.Thenwatchtheballfall backtothebottom.

5. Clickthelinkinthelabbookthatcontainsyourdata.Youmaywanttocopyand pasteitintoaspreadsheetprogram.Fromthedata you shouldfindfive different locationsoftheball and compare theball’spotentialandkinetic energies atthosepoints.First you will find andrecordthedifferent velocities andtheheightsatwhichtheballhadthose velocities.Thebeginningwaswhen theballfirstgothit.Recordtheball’s velocityright afteritwashit(thefirstdata pointwherevelocity≠0.)Thenfindamiddleheightinthedata andrecordit and thevelocity oftheball atthat height.Dothesameforthetop, themiddle

onthewaydown, andthenthebottomagain. RecordtheinformationinData

Table1.

Data Table 1

BallPosition / Height(m) / Velocity(m/s)
Beginningbottom
Middlegoingup
Top
Middlecomingdown
Endbottom

6. Nowyoucancalculatethegravitationalpotentialenergyandthekinetic energyoftheballatthedifferentpositions.Recallthatgravitational potentialenergyisduetotheworkofliftingtheballagainstgravity.Soyou onlyneedtoknowtheheightoftheballoffthegroundy(m).Recordyour calculationsinDataTable2.Usetheequation:

PE=mgh

wheremismass ofball,gistheaccelerationduetogravity,andhisheightof ballfromground.

7. Recallthat thekineticenergyofanobjectdependsonitsmassand thespeed orvelocitythatit ismoving.Calculatethekineticenergyusingtheequation:

KE = mv2

wheremismass,andvisthevelocityoftheball.

Data Table 2

BallPosition / PotentialEnergy / KineticEnergy
Startingbottom
Middlegoingup
Top
Middlecomingdown
Endingbottom

40EnergyConversions

Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions.

Copyright © 2008 by Pearson Education, Inc.

AnalyzeandConclude

1. MakingGeneralizationsWhatdeterminespotentialenergy?Kinetic energy?

2. InterpretingDataWhendidtheballhavethemostpotentialenergy?

Why?

3. InterpretingDataWhendidtheballhavethemostkineticenergy?

4. ApplyingConceptsWhatistherelationshipbetweenthePEatthetopof theramp,andtheKEatthebottomoftheramp?

5. DrawingConclusionsWheredidtheenergygofromthetopoftheramp to thebottom?Explainthemotionof theballthroughouttheexperimentin termsofpotentialandkineticenergy.