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ForceandMotionStudyGuide
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Vocabularytoknow:
Inertia:anobject’stendencytoresistachangeinmotion
Force:apushorapullonanobject
Gravity:aforcethatpullsobjectstowardtheEarth
Friction:resistancetoanymotion
Magnitude:thestrengthofaforce
Weight:thepullofgravityonanobject’smass
Speed:distancedividedbytime
Velocity:anobject’sspeedanddirection
Matter:anythingthathasmassandtakesupspace
Acceleration:achangeinspeedordirection(achangeinvelocity)
BalancedForces:equalandoppositeforcesresultinginnomotion
UnbalancedForces:unequalforcesresultinginmotion
Newton’s1stLaw:Lawofinertia:anobjectatrestwillstayatrestoranobjectinmotionwillstayin
motionuntilanoutsideforceactsuponit.
Newton’s2ndLaw:Lawofacceleration:whenanunbalancedforceisappliedtoanobject,theobject
accelerates.
Newton’s3rdLaw:Lawofaction/reaction:foreveryactionthereisanequalandoppositereaction
Calculatingspeedandvelocity:
Remember,velocityisspeedANDdirection.Speeddoesn’tincludedirection,justthetimeanddistance.
Refertoyourformulatriangleinyoursciencenotebook.
Examples: Whatisthespeedofadogrunning13kmnorthin30minutes?26km/hour
Whatisthevelocityofanobjectmoving14mileseastin60minutes?14mpheast
CalculatingSpeedandVelocityPracticeProblems:
1)Whatisthespeedofanobjecttraveling45meterssouthin30minutes? 2)Whatisthevelocityofanobjecttraveling60kmeastin2hours?
3)Whatisthevelocityofanobjectthatismoving4cmsouthevery15minutes?
4)Whatisthespeedofacarthatisdriving82kmnorthevery10minutes? CalculatingNetForce:
Tofindthenetforceyoushouldsubtractforceswhentheyareactinginoppositedirections.Iftheforces
areactinginthesamedirectionyouwouldaddtheforcestogether.ForceismeasuredinNewtons(N).
Examples:
Mollypullswith20NofforcetotheleftwhileMinaispullingwith45Nof
forcetotheright.Whatisthenetforce?Theforcesareoppositesoyou
subtract45–20=25Nwithmotiontotheright.Drawapicturetohelpyou
solvetheproblem
20N 45N JoeandDonarepushingaboxtotheleft.Joeispushingwith10Nofforce
10N+15N=25N andDonispushingwith15Nofforce.Whatisthenetforceonthebox?The
forcesareinthesamedirectionssoyouadd10+15=25N.
Ifthefrictionforceactingontheboxis25N,whatwouldthenetforcebe?
Wouldtherebemotion?ThecombinedforceontheboxfromJoeandDonis
25Ntotheright.Frictionactsintheoppositedirection.Subtract25–25=0
N.Thenetforceis0Nwhichmeanstheforcesarebalancedandthereisno
25N
motion.
Calculatingnetforcepracticeproblems:
1)Mrs.Banisterismovingherfilingcabinet.Sheispushingonthecabinetwithaforceof25N.The
frictionforcebetweenthecabinetandtheflooris25N.Whatisthenetforce?Istheremotion? 2)Ms.BaileydecidedtohelpMrs.Banistermoveherfilingcabinet.Isn’tshenice!InadditiontoMrs.
Banister’s25Nofforce,Ms.Baileypushedwith25Nofforceaswell.Ifthefrictionforcestayedthesame
(25N),whatwouldbethenewnetforce?Istheremotion?
3)Joeispushmowinghislawn.Thefrictionforcebetweenthelawnmowerandthegroundis40N.IfJoe
ispushingthemowerwith50Nofforce,whatisthenetforce?Istheremotion?
A)10N,nomotionB)10N,motionC)90N,nomotionD)90N,motion
4)Jackismovinghisdeskintheclassroom.Heispullingonhisdeskwith13Nofforce.Ifthefriction
forcebetweenthedeskandtheflooris8N,whatisthenetforce?Istheremotion?
A)21N,motionB)5N,motionC)3N,nomotionD)21N,nomotion