Chapter-2-Motion-in-One-Dimension-Sharyland-ISD-Overview：2章一維運(yùn)動(dòng)-Sharyland-ISD概述課件

SECTION1DISPLACEMENTANDVELOCITYChapter2

MotioninOneDimensionMotionMotionhappensallaroundusindifferentdirectionsanddifferentspeeds.

One–dimensionalmotionisthesimplestformofmotion.Example:Commutertraincanmoveonlyforwardandbackwardalongthestraighttrack.MotionMotiontakesplaceovertimeanddependsonframeofreference.FrameofReference–whatyouusetomeasurechangesinposition.FrameofReferenceFrameofreferenceisbasicallywhatyouareusingtomeasurechangesinpositionofanobject.Ifanobjectisatrest(notmoving),itspositiondoesnotchangewithrespecttoaframeofreference.Asanyobjectmovesfromonepositiontoanother,thelengthofthestraightlinedrawnfromitsinitialpositiontotheobject’sfinalpositioniscalledthedisplacementoftheobject.DisplacementDisplacementisachangeinposition.Displacement=finalposition–initialposition.Displacementisnotalwaysequaltothedistancetraveled.Displacementcanbepositiveornegative!inyourbook(unlessstatedotherwise)RIGHT&UPwillbeconsideredpositiveandLEFT&DOWNwillbeconsiderednegative.

DisplacementDisplacementisnotalwaysequaltothedistancetraveled.DisplacementDisplacementcanbepositiveornegative.ThereareonlytwodirectionstomoveonXaxisandtwotomoveonYaxisRight:PositiveLeft:NegativeUp:PositiveDown:NegativeDisplacementVelocityAverageVelocityisdisplacementofanobject(Δx)dividedbytimeinterval(Δt).Equation:vavg

=Δx=xf-xi

Δttf-tiAverageVelocitycanbepositiveornegativedependingonthesignofthedisplacement.Ifdisplacementisnegative,avg.velocityisnegative.TimeintervalisalwayspositiveGuidedPracticeOpenBookstopg.44Velocityisnotthesameasspeed.Velocitydescribesmotionwithdirectionandmagnitude(numericalvalue);speedhasnodirection,onlymagnitude. Ex:55m/sand55m/sNorthVelocityVs.SpeedSECTION2ACCELERATIONChapter2

OneDimensionalMotionVelocitycanbeinterpretedgraphically…Themotionofanobjectmovingwithconstantvelocitywillprovideastraight-linegraphofpositionversustime.Theslopeofthisgraphindicatestheaveragevelocity.2-2AccelerationAccelerationmeasurestherateofchangeinvelocity(usuallypersecond).Accelerationhasdimensionsoflengthdividedbytime

squared.TheunitsofaccelerationinSIaremeterspersecondpersecond.

m/s2AccelerationThreewaystoAccelerate:ObjectspeedingupObjectslowingdownObjectchangingdirectionFormulaforAverageAccelerationAverageAcceleration= Changeinvelocity timerequiredforchange OR aavg=vf–vi tf-tiLet’sPracticewithAverageAcceleration...Turntopage49inyourbooksandwecanworkonpractice2B.AccelerationisVelocity/TimeAccelerationhasdirectionandmagnitude.Theslopeandshapeofagraphplottingvelocityvs.timedescribestheobject’smotion.Whenvelocityongraphis

increasing:accelerationispositive

decreasing:accelerationisnegative

constant:thereisnoaccelerationMotionwithconstantacceleration.VelocityVs.TimeGraphsReview-DisplacementwithconstantuniformAccelerationDisplacementdependsonacceleration,initialvelocity,andtime.Displacementwithconstantuniformaccelerationisequalto:

ΔX=?(initialvelocity+finalvelocity)(timeinterval)SolvingforFinalVelocity(Vf)Finalvelocitydependsoninitialvelocity,acceleration,andtime.

aavg=Δv=

vf

-vi

Δt

tf-tiDisplacementofanobjectdependsoninitialvelocity,finalvelocity,andtime.

Δx=?(vi+vf)Δt

Howcanwesolvefordisplacementifwedon’thavefinalvelocity?SolvingforVf&DisplacementByrearrangingtheequationforacceleration,wecanfindavalueforthefinalvelocity.

vf

=vi+aΔtTofinddisplacementofanobjectmovingwithuniformaccelerationwesubstitutetheaboveexpressionforvfintoourdisplacementformula.

Δx=

vi

Δt+?a(Δt)2

GuidedPracticeSampleProblem2Donpg.55FinalVelocityafterAnyDisplacementWecanalsoobtainanexpressionthatrelatesdisplacement,velocity,andaccelerationwithoutusingtimeinterval.vf2=vi2+2aΔxGuidedPracticeSampleProblem2Epg.57SECTION3FALLINGOBJECTSChapter2

OneDimensionalMotionFreeFallFreefallisaccelerationduetogravity.Freefallaccelerationisconstant.

Magnitudeoffreefallis9.81m/s2Directionoffreefallisdirecteddownward.negativedirection(-)Freefallisdenotedwiththesymbolg.(Sometimesmaybe‘a(chǎn)’foraccelerationduetogravity)FreeFallInavacuum,intheabsenceofairresistance,allobjectsfallatthesamerate.Whatgoesupmustcomedown.Whatcausesanobjectthathasbeenthrownupintotheairtocomebackdown?Free-FallAccelerationduetogravityisalwaysdirecteddownwardandpullinganobjecttowardsEarth’ssurface.RecallInformationRememberwelearnedaboutaform