professor jasper halekas van allen 70 mwf 12:30-1:20 lecturejhalekas/teaching/physiv_2018/...¡what...
TRANSCRIPT
¡ First,openthewebpage(https://rwpoll.comorhttps://account.turningtechnologies.com)ortheResponseWareapp§ EnterthesessionIDontheboard
¡ WaituntilIopenpolling(arrowchangestosquareonmyscreen)
¡ EnterA,B,C,D,orE§ Canchangeansweraslongaspollingstillopen
¡ AfterIclosepolling,wewillseeahistogramoftheresults
¡ Whatintrophysicsseriesdidyoutake?
A. PhysicsI,II,&IIIhere
B. IntroductoryPhysicsI&IIhere
C. Anintrophysicsseriesatanotherinstitution
D. Didnottakeanintrophysicsseries
E. Other
¡ Whenyougraduate,doyouwantto:
A. Getahigherdegreeinphysics?
B. Getahigherdegreeinanothersubject?
C. Workinengineering,industry,computerscience,
datascience,orothertechnicalfield?
D. Workinanon-technicalfield?
E. Fleethecountry?
¡ Areyoulookingforwardtobeingabletoexplainquantummechanicstoyourfriendsand/orsignificantother?
A. Yes,Ienjoydemonstratingmyintellectualacumen
B. No,Ihavebetterthingstotalkabout
C. MysignificantotherwouldleavemeifIbroughtup
quantummechanics
D. WhytheheckelsewouldIbetakingthisclass!!??
Attimet=0,thetwoframescoincide.AballisatrestinframeS.Itspositionis• x=2minS• x’=2minS’
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u
FrameS’ismovingtotheright(relativetoS)atu=1m/s.Attimet=3sec,thepositionoftheballis• x=2minS• x’=-1minS’
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u
Attime0,theballwasatx=x’.Attimetlater,theballisstillatxinSbutwhereisitinS’atthesametimet?a)x’=x b)x’=x+ut c)x’=x-ut
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u
Attime0,theballwasatx=x’.Attimetlater,theballisstillatxinSbutwhereisitinS’atthesametimet?a)x’=x b)x’=x+ut c)x’=x-ut
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u
ʹx = x −utʹy = yʹz = zʹt = t
vx ' =d ʹx (t)dt
=ddt
x(t)−ut( ) = dx(t)dt
−u = vx −u
Note:Assumesframesalignedatt=0
Thelawsofphysicsarethesameinallinertialframesofreference.
Thespeedoflightisthesameinallinertialframesofreference.
Anobserverat(0,0)hasaclock;eventstherearecovered.Anobserverat(3m,2m)hadbetterhaveaclocktoo,ifwewanttoknowabouteventsthere.And,thetwoclockshadbettershowthesametime.
Attheorigin,atthreeo’clock,theclocksendsoutalightsignaltotelleverybodyit’sthreeo’clock.Timepassesasthesignalgetstotheclockatx=3m.
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Whenthesignalarrives,theclockatx=3missetto3:00plusthe10nsdelay(whichiscalculatedbyknowingthespeedoflightc).
Cory
L R
Coryisthemiddleofarailroadcar,andsetsoffafirecracker.Lightfromtheexplosiontravelstobothendsofthecar.WhichenddoesitreachfirstaccordingtoCory?
a)bothendsatonceb)theleftend,Lc)therightend,R
u
Cory
L R
Coryisthemiddleofarailroadcar,andsetsoffafirecracker.Lightfromtheexplosiontravelstobothendsofthecar.WhichenddoesitreachfirstaccordingtoCory?
a)bothendsatonceb)theleftend,Lc)therightend,R
u
Chrissieisstandingatrestnexttothetraintracks,watchingthetrainmovetotheright.AccordingtoChrissie,whichendofthetraincardoesthelightreachfirst?
a)bothendsatonceb)theleftend,Lc)therightend,R
L R
v
Chrissie
Chrissieisstandingatrestnexttothetraintracks,watchingthetrainmovetotheright.AccordingtoChrissie,whichendofthetraincardoesthelightreachfirst?
a)bothendsatonceb)theleftend,Lc)therightend,R
L R
v
Chrissie
u
...-3-2-10123...Chrissie
Cory
SupposeCory’sfirecrackerexplodesattheoriginofChrissie’sreferenceframe.
L R
ThelightspreadsoutinChrissie’sframefromthepointshesawitexplode.Becausethetraincarismoving,thelightinChrissie’sframearrivesattheleftendfirst.
uCory
L R
...-3-2-10123...Chrissie
uCory
L R
...-3-2-10123...Chrissie
Sometimelater,inChrissie’sframe,thelightcatchesuptotherightendofthetrain.
L R
0
uL R
uL R
uL R
uL R
Cory:inthetrain Chrissie:ontheplatform
0
EventL:(x=-3,t=3s)
EventR:(x=+3,t=3s)
EventL’:(x’=-2,t’=2s)
EventR’:(x’=+5,t’=4s)
x’x
uL R
Corysays:‘Simultaneous!’ Chrissiesays:‘Notsimultaneous!’
Joey Brad
h
u · Δt/2
JoeyandBradmeasurethetimeinterval:
ButGarethmeasuredΔt’=Δt0=2h/c!!
Δt = 2hcγ, γ =
1
1− u2
c2
¡ “ProperTime”=Δτ=Δt0§ Thetimeintervalmeasuredinaframewherethetwoeventsoccuratthesamespatialcoordinate–i.e.theframemovingwithyourclock
¡ ThetimeintervalΔtmeasuredinanyotherframemovingwithrespecttothisframewillbelonger§ Δt=γΔt0
¡ Amuonlifetimeis2.2μsinitsrestframe,butitisobservedtolivefor220μsintravelingfromtheupperatmospheretotheground.Whichisclosesttoitsvelocityaccordingtotheexternalobserver?
A. v=√(0.9)cB. v=√(0.99)cC. v=√(0.999)cD. v=√(0.9999)c
¡ Amuonlifetimeis2.2μsinitsrestframe,butitisobservedtolivefor220μsintravelingfromtheupperatmospheretotheground.Whichisclosesttoitsvelocityaccordingtotheexternalobserver?
A. v=√(0.9)cB. v=√(0.99)cC. v=√(0.999)cD. v=√(0.9999)c
β=v/c=√(0.9999)=0.99995