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IntroductoryPhysics
PHYS101
Dr RichardH.CyburtOfficeHours
TRF9:30-11:00am
AssistantProfessorofPhysics
F12:30-2:00pm
Myoffice:402cintheScienceBuilding
Myphone:(304)384-6006
Meetingsmayalsobearrangedatothertimes,
byappointment
Myemail:[email protected]
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Checkmyscheduleonmyofficedoor.
ofme.
PHYS101
PHYS101:IntroductoryPhysics
400
Lecture:8:00-9:15am,TRScienceBuilding
Lab1:3:00-4:50pm,FScienceBuilding304
Lab2:1:30-3:20pm,MScienceBuilding304
Lab3:3:30-5:20pm,MScienceBuilding304
Lab20:6:00-7:50pm,MScienceBuilding304
NoLab:Fri,Sep2:Extendedofficehoursin304,3:00-4:50pm
PHYS101
MasteringPhysicsOnline
GotoHYPERLINK"http://www.masteringphysics.com."www.masteringphysics.com.
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PHYS101
Midterm1
ReviewSession:Wednesday,Sept.7,7:00-9:00pmScienceBuilding300.
Midterm:Thursday,Sept.8,8:00-9:15amScienceBuilding400.
Chapters1-4,Notcircularmotion
PHYS101
IntroductoryPhysics
PHYS101
DouglasAdams
Hitchhiker’sGuidetotheGalaxy
PHYS101
You’realreadyknowphysics!
Youjustdon’tnecessarilyknowtheterminologyand
languageweuse!!!
PhysicsofNASCAR
PhysicsofAngerBirds
PHYS101
Inclass!!
PHYS101
Thislecturewillhelpyouunderstand:
SolvingProjectileMotionProblems
MotionandForces(Newton’sFirstLaw)
Whatkindofforcesarethere?
Identifyingforces
Whatdoforcesdo?
Newton’sSecondLaw
PHYS101
Section3.7Projectile
Motion:
SolvingProblems
©2015PearsonEducation,Inc.
ProjectileMotionProblems
Text:p.83
©2015PearsonEducation,Inc.
ProjectileMotionProblems
Text:p.83
©2015PearsonEducation,Inc.
TheRangeofaProjectile
Therange ofaprojectileisthe
horizontaldistancetraveled.
Forsmallerobjectsairresistanceis
critical,andthemaximumrange
comesatananglelessthan45°.
©2015PearsonEducation,Inc.
QuickCheck3.18
Projectiles1and2arelaunchedoverlevelgroundwiththesamespeedbutat
differentangles.Whichhitsthegroundfirst?Ignoreairresistance.
◦
◦
◦
◦
Projectile1hitsfirst.
Projectile2hitsfirst.
Theyhitatthesametime.
There’snotenoughinformationtotell.
©2015PearsonEducation,Inc.
QuickCheck3.18
Projectiles1and2arelaunchedoverlevelgroundwiththesamespeedbutatdifferentangles.
Whichhitsthegroundfirst?Ignoreairresistance.
◦
◦
◦
◦
Projectile1hitsfirst.
Projectile2hitsfirst.
Theyhitatthesametime.
There’snotenoughinformationtotell.
©2015PearsonEducation,Inc.
ExampleProblem
Agrasshoppercanjumpadistanceof30in(0.76m)fromastanding
start.
◦ Ifthegrasshoppertakesoffattheoptimalangleformaximumdistanceofthe
jump,whatistheinitialspeedofthejump?
◦ Mostanimalsjumpataloweranglethan45°.Supposethegrasshoppertakes
offat30° fromthehorizontal.Whatjumpspeedisnecessarytoreachthe
noteddistance?
©2015PearsonEducation,Inc.
BrainFart
𝑥" = 0
𝑦" = 0
𝑥% = 𝐷
𝑦% = 𝐷
(𝑣) )" = 𝑣 cos 𝜃
(𝑣1 )" = 𝑣 sin 𝜃
(𝑣) )% = 𝑣 cos 𝜃
(𝑣1 )% = −𝑣 sin 𝜃
𝑎) = 0
𝑎1 = −𝑔
(𝑣1 )% = (𝑣1 )" + 𝑎1 ∆𝑡
−𝑣 sin 𝜃 = 𝑣 sin 𝜃 − 𝑔∆𝑡
:
;
𝑥% = 𝑥" + (𝑣) )" ∆𝑡 + 𝑎) ∆𝑡 ;
2𝑣 sin 𝜃 = 𝑔∆𝑡 = g
𝐷 = 𝑣 cos 𝜃 ∆𝑡
∆𝑡 =
<
= >?@ A
𝒗𝟐
PHYS101
=
𝒈𝑫
𝟐 𝐬𝐢𝐧 𝜽 𝐜𝐨𝐬 𝜽
<
= >?@ A
or𝑫 =
𝒗𝟐
𝟐 𝒔𝒊𝒏 𝜽 𝒄𝒐𝒔 𝜽
𝒈
Section4.1Motionand
Forces
©2015PearsonEducation,Inc.
WhatCausesMotion?
Intheabsenceoffriction,ifthesledismoving,itwillstayinmotion.
©2015PearsonEducation,Inc.
WhatCausesMotion?
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WhatIsaForce?
Aforce isapush orapull.
Aforceactsonanobject.
Everyforcehasanagent,somethingthatacts
orpushesorpulls.
©2015PearsonEducation,Inc.
WhatIsaForce?
r
F
Aforce isavector.Thegeneralsymbolfora
forceisthevectorsymbol.Thesizeor
strengthofsuchaforceisitsmagnitudeF.
Contactforcesareforcesthatactonanobject
bytouchingitatapointofcontact.
Long-rangeforces areforcesthatactonan
objectwithoutphysicalcontact.
©2015PearsonEducation,Inc.
ForceVectors
Text:p.100
©2015PearsonEducation,Inc.
ForceVectors
©2015PearsonEducation,Inc.
CombiningForces
Experimentsshowthatwhen
r r r
severalforcesare
F1 , F2 , F3 ,K
exertedonanobject,thecombine
toformanetforcethatisthe
vectorsumofalltheforces:
Thenetforceissometimescalled
theresultantforce.Itisnotanew
force.Instead,weshouldthinkof
theoriginalforcesbeingreplaced
r
by.
Fnet
©2015PearsonEducation,Inc.
COMP:Symbolswith
overarrows are
MathType
QuickCheck4.1
Thenetforceonanobjectpointstotheleft.Twoof
threeforcesareshown.Whichisthemissingthird
force?
A.
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B.
C.
D.
QuickCheck4.1
Thenetforceonanobjectpointstotheleft.Twoof
threeforcesareshown.Whichisthemissingthird
force?
A.
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B.
C.
Vertical components cancel
D.
Section4.2AShort
CatalogofForces
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Weight
Thegravitationalpullof
theearthonanobjecton
ornearthesurfaceofthe
earthiscalledweight.
Theagentfortheweight
forcesistheentireearth
pullingonanobject.
Anobject’sweight
vectoralwayspoints
verticallydownward, no
matterhowtheobjectis
moving.
©2015PearsonEducation,Inc.
SpringForce
Springscomeininmanyforms.
Whendeflected,theypushorpullwithaspringforce.
©2015PearsonEducation,Inc.
TensionForce
Whenastringorropeorwirepullsonanobject,itexertsacontact
forcethatwecallthetensionforce.
Thedirectionofthetensionforceisalwaysinthedirectionofthe
stringorrope.
©2015PearsonEducation,Inc.
NormalForce
Theforceexertedonanobjectthatis
pressingagainstasurfaceisina
directionperpendicular tothesurface.
Thenormalforce istheforceexerted
byasurface(theagent)againstan
objectthatispressingagainstthe
surface.
©2015PearsonEducation,Inc.
NormalForce
Thenormalforceisresponsibleforthe“solidness”ofsolids.
r
Thesymbolforthenormalforceis.
n
COMP:n[overarrow]
isMathType.
©2015PearsonEducation,Inc.
Friction
Friction,likethenormalforce,isexertedbyasurface.
Thefrictionalforceisalwaysparalleltothesurface.
r
Kineticfriction,denotedby,actsasanobjectslidesacrossasurface.Kinetic
fk
frictionisaforcethatalways“opposesthemotion.”
r
fs
Staticfriction,denotedby,istheforcethatkeepsanobject“stuck”ona
surfaceandpreventsitsmotionrelativetothesurface.Staticfrictionpointsin
thedirectionnecessarytoprevent motion.
©2015PearsonEducation,Inc.
Friction
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Drag
Theforceofafluid(like
airorwater)onamoving
objectiscalleddrag.
Likekineticfriction,drag
pointsoppositethe
directionofmotion.
Youcanneglectair
resistanceinall
problemsunlessa
problemexplicitlyasks
youtoincludeit.
©2015PearsonEducation,Inc.
Thrust
Thrust isaforcethatoccurs
whenajetorrocketengine
expelsgasmoleculesathigh
speed.
Thrustisaforceoppositethe
directioninwhichtheexhaust
gasisexpelled.
©2015PearsonEducation,Inc.
ElectricandMagneticForces
Electricityandmagnetism,likegravity,exertlong-rangeforces.
Theforcesofelectricityandmagnetismactonchargedparticles.
Theseforces—andtheforcesinsidethenucleus—won’tbe
importantforthedynamicsproblemsweconsiderinthenextseveral
chapters.
©2015PearsonEducation,Inc.
QuickCheck4.2
Aballrollsdownaninclineandoffahorizontal
ramp.Ignoringairresistance,whatforceor
forcesactontheballasitmovesthroughthe
airjustafterleavingthehorizontalramp?
◦ Theweightoftheballactingverticallydown.
◦ Ahorizontalforcethatmaintainsthemotion.
◦ Aforcewhosedirectionchangesasthedirectionofmotionchanges.
◦ Theweightoftheballandahorizontalforce.
◦ Theweightoftheballandaforceinthedirectionofmotion.
©2015PearsonEducation,Inc.
QuickCheck 4.2
Aballrollsdownaninclineandoffahorizontal
ramp.Ignoringairresistance,whatforceor
forcesactontheballasitmovesthroughthe
airjustafterleavingthehorizontalramp?
◦ Theweightoftheballactingverticallydown.
◦ Ahorizontalforcethatmaintainsthemotion.
◦ Aforcewhosedirectionchangesasthedirectionofmotionchanges.
◦ Theweightoftheballandahorizontalforce.
◦ Theweightoftheballandaforceinthedirectionofmotion.
©2015PearsonEducation,Inc.
QuickCheck4.3
Asteelbeamhangsfromacableasacraneliftsthebeam.Whatforcesacton
thebeam?
◦
◦
◦
◦
Gravity
Gravityandtensioninthecable
Gravityandaforceofmotion
Gravityandtensionandaforceofmotion
©2015PearsonEducation,Inc.
QuickCheck4.3
Asteelbeamhangsfromacableasacraneliftsthebeam.Whatforcesacton
thebeam?
◦
◦
◦
◦
Gravity
Gravityandtensioninthecable
Gravityandaforceofmotion
Gravityandtensionandaforceofmotion
©2015PearsonEducation,Inc.
QuickCheck4.4
Abobsledderpusheshersledacrosshorizontalsnowtogetitgoing,thenjumps
in.Aftershejumpsin,thesledgraduallyslowstoahalt.Whatforcesactonthe
sledjustaftershe’sjumpedin?
◦
◦
◦
◦
◦
Gravityandkineticfriction
Gravityandanormalforce
Gravityandtheforceofthepush
Gravity,anormalforce,andkineticfriction
Gravity,anormalforce,kineticfriction,andtheforceofthepush
©2015PearsonEducation,Inc.
QuickCheck4.4
Abobsledderpusheshersledacrosshorizontalsnowtogetitgoing,thenjumps
in.Aftershejumpsin,thesledgraduallyslowstoahalt.Whatforcesactonthe
sledjustaftershe’sjumpedin?
◦
◦
◦
◦
◦
Gravityandkineticfriction
Gravityandanormalforce
Gravityandtheforceofthepush
Gravity,anormalforce,andkineticfriction
Gravity,anormalforce,kineticfriction,andtheforceofthepush
©2015PearsonEducation,Inc.
Section4.3Identifying
Forces
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IdentifyingForces
Text:p.105
©2015PearsonEducation,Inc.
IdentifyingForces
©2015PearsonEducation,Inc.
ConceptualExample4.1:Identifying
forcesonabungeejumper
Abungeejumperhasleaptoffabridgeandisnearingthebottomof
herfall.Whatforcesarebeingexertedonthebungeejumper?
©2015PearsonEducation,Inc.
ConceptualExample4.2:Identifying
forcesonaskier
Askierisbeingtowedupasnow-coveredhillbyatowrope.What
forcesarebeingexertedontheskier?
©2015PearsonEducation,Inc.
Section4.4WhatDo
ForcesDo?
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WhatDoForcesDo?
Howdoesanobjectmove
whenaforceisexertedonit?
©2015PearsonEducation,Inc.
WhatDoForcesDo?
Astheblockstartstomove,inordertokeepthepulling
forceconstantyoumustmoveyourhandinjusttheright
waytokeepthelengthoftherubberband—andthusthe
force—constant.
©2015PearsonEducation,Inc.
WhatDoForcesDo?
Theexperimentalfindingsofthemotionofobjectsactedonbyconstantforces
are:
Anobjectpulledwithaconstantforcemoveswithaconstantacceleration.
Accelerationisdirectlyproportionaltoforce.
Accelerationisinverselyproportional toanobject’smass.
©2015PearsonEducation,Inc.
QuickCheck4.5
Acartispulledtotherightwitha
constant,steadyforce.Howwill
itsaccelerationgraphlook?
A.
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B.
C.
QuickCheck4.5
Acartispulledtotherightwitha
constant,steadyforce.Howwillits
accelerationgraphlook?
A.
B.
A constant force produces a constant acceleration.
©2015PearsonEducation,Inc.
C.
Example4.4Findingthemassofan
unknownblock
Whenarubberbandisstretchedtopullona1.0kgblockwithaconstantforce,
theaccelerationoftheblockismeasuredtobe3.0m/s2.
Whenablockwithanunknownmassispulledwiththesamerubberband,using
thesameforce,itsaccelerationis5.0m/s2.
Whatisthemassoftheunknownblock?
PREPARE Eachblock’saccelerationisinverselyproportionaltoitsmass.
©2015PearsonEducation,Inc.
Example4.4Findingthemassofan
unknownblock(cont.)
SOLVE WecanusetheresultoftheInverselyProportionalRelationshipsboxto
write
ASSESS Withthesameforceapplied,theunknownblockhadalargeracceleration
thanthe1.0kgblock.Itmakessense,then,thatitsmass—itsresistanceto
acceleration—islessthan1.0kg.
©2015PearsonEducation,Inc.
Section4.5Newton’s
SecondLaw
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Newton’sSecondLaw
Aforcecausesanobjecttoaccelerate.
Theaccelerationa isdirectlyproportionaltotheforceFandinversely
proportionaltothemassm:
Thedirectionoftheaccelerationisthesameasthedirectionoftheforce:
©2015PearsonEducation,Inc.
Newton’sSecondLaw
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