Download Chapter 4 study guide Work is done when a force causes an object

Chapter4studyguide
Workisdonewhenaforcecausesanobjecttomoveinthedirectionoftheforce.
Example:acupofcoffeeissittingonthecounter(ithaspotentialenergy).Yourcatisajerkandknocksthecupoffthe
counterandisinmotionfallingtowardsthefloor(kineticenergy).
Aforcedoesnotalwaysresultinworkbeingdone.
Example:youhelppushalargerockfromyourbackyardtowardsthewoods,buttherockdoesnotmove.Workhasnot
beendoneeventhoughyouappliedforce.
Theformulaforcalculatingtheamountofwork(W)doneinmovinganobjectrequiresyouto
multiplytheforce(F)bythedistance(d)theobjectmoved.W=FXd.
Forceisexpressedinnewtons(N).Metricisuniversallyusedinscience,andoneofthetoolsfor
measuringdistanceisameterstick.Toexpresswork,usethenewton-meter(NXm).
Joule:becauseworkisthetransferofenergytoanobject,thejoule(j)isalsoaunitusedtomeasure
energy.
Powerishowfastworkisdone.Tocalculatepower,divideworkbytime.P=w/t
Theunitusedtoexpresspowerisjoulespersecond(J/s),alsocalledawatt.RecallyourPowerful
Workoutactivity(stairclimbing).Completingthestairclimbfastorslowdidnoteffecthowmuchworkyou
did,onlyhowquicklyyoudidthework.
Machine:adevicethatmakesworkeasierbychangingthesizeordirectionofaforce.Amachine
allowsforcetobeappliedoveragreaterdistance,whichmeansthatlessforcewillbeneededfor
thesameamountofwork.
Workinputistheworkdoneonamachine,theworkdonebythemachineisworkoutput.Work
inputisalwaysgreaterthanworkoutputdueto(examples:friction,heatloss).
Force-distancetrade-off:whenamachinechangesthesizeoftheforce,thedistancethrough
whichtheforceisexertedmustalsochange.Forceordistancecanincrease,butbothcannot
increaseatthesametime.Whenoneincreases,theothermustdecrease(thinkofthepulleyactivity
whereyoudidthesamework,butwiththestringdoubledinlength,youdidthesameworkwitha
greaterlengthofstring).
Mechanicaladvantage:isthenumberoftimesthemachinemultipliesforce.Onepulleydidnot
haveamechanicaladvantage.Twopulleyshadamechanicaladvantageof2.Mechanicaladvantage
iscalculatedlikethis,mechanicaladvantage(MA=outputforce/inputforce).
Mechanicalefficiency:isacomparisonofamachine’sworkoutputwiththeworkinput.
Mechanicalefficiency=workoutput/workinputX100
Typesofmachines
Levers(hammerpullinganail),pulleys(blockandtacklewith4ropesegmentshasamechanical
advantageof4),wheelandaxle(turningafaucetonoroff),wedge(apairofinclinedplanes
workingtogether{thinkofaknifecuttingawatermeloninhalf},screw(aninclinedplanewrapped
inaspiralaroundacylinder).