Physics Unit 2
Friday 17th of June
P2.1 Forces and their effects
Make sure you are familiar with…
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Interpreting velocity-time and distance-time graphs
Evaluating factors affecting stopping distances
Evaluating the shape and power of vehicles and how this will affect their motion
Consider the motion of falling objects
1.
Resultant Forces
a.
Objects exert equal and opposite force on each other when they interact
b.
Forcescanbecombinedintoasingle“resultant”force
c.
Aresultantforcewillcreateachangeinspeedordirection
d.
Iftheresultantforceis…
i. Zeroonastationaryobject,itwillnotmove
ii. Zeroonamovingobject,itwillstayataconstantspeed
iii. Nonzero,theobjectwillaccelerateinthedirectionoftheforce
Forcesandmotion
a.
Accelerationisdeterminedbytheresultantforceandthemass:F=mxa
b.
Thegradientofadistance-timegraphrepresentsspeed
c.
Thevelocityofanobjectisitsspeedinagivendirection
d.
Accelerationisgivenbytheequation:𝑎 = $%&
'
e.
Thegradientofavelocity-timegraphrepresentsacceleration
Forcesandbraking
a.
Whenavehicletravelsatasteadyspeedtheresistiveforcesbalancethe
drivingforces;muchoftheresistancecomesfromairresistance
b.
Thegreaterthespeedofavehicle,thegreatertheforcerequiredtostopit
inacertaindistance
c.
Thestoppingdistanceofavehicleisthesumofthedistancethevehicletravels
duringthethinkingtimeandthedistanceittravelsunderbraking
d.
Adriver’sreactiontimemaybeaffectedbytiredness,drugsandalcohol
e.
Whenthebrakesofavehicleareapplied,workdonebythefrictionbetween
thebrakesandthewheelreducesthekineticenergyofthevehicleandthe
temperatureofthebrakesincrease
f.
Avehicle’sbrakingdistancecanbeaffectedbyadverseroadandweather
conditionsandtheconditionofthevehicle
2.
3.
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4.
5.
Forces and terminal velocity
a.
The faster an object moves through a liquid or gas, the greater the
resistiveforcetheyexperience
b.
Anobjectfallingthroughaliquidorgaswillinitiallyacceleratedueto
gravity.Eventuallytheresultantforcewillfalltozeroandtheobject
willfallataterminalvelocity
c.
Candidatesshoulddrawandinterpretvelocity-timegraphsforobjects
thatreachterminalvelocity
d.
Calculatetheforceofgravity(weight)actingonanobjectusingthe
formulaW=mxg
Forcesandelasticity
a.
Forcesmaychangetheshapeofanobject
b.
Whenaforceisappliedtoanelasticobjectsuchasaspring,thiswillresult
in the object stretching and storing elastic potential energy
c.
For an object that is able to recover its original shape, elastic potential
energyisstoredintheobjecttochangeitsshape
d.
Theextensionofanelasticobjectisdirectlyproportionaltotheforceapplied
uptothelimitofproportionality
e.
TheforcewillfollowtheequationF=kxe
wherekisthespringconstantandeistheextension
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P2.2 Speeding up or slowing down
Make sure you are familiar with…
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Evaluating different types of braking system, including modern systems such as regenerative braking
Talking about changes in momentum and energy with respect to air bags, crumple zones, seat belts and side impact bars during car
crashes
1.
Forces and energy
a.
When a force causes an object to move through a distance, work is done
b.
Work done, force and distance are related by the equation W = F x d
c.
Energyistransferredwhenworkisdone
d.
Workisdoneagainstfrictionalforceswhenobjectsmovealongasurface
e.
Poweristheworkdoneorenergytransferredinagiventime,thiscanbe
determinedusingtheequationP=E/t
f.
Gravitationalpotentialenergyistheenergythatistransferredbyanobject
whenitmovesthroughagravitationalfield,thischangeinenergycanbe
determinedusingtheequationE=mxgxh
g.
Anobjectmovingwithspeed,v,possesseskineticenergy;thiscanbe
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foundusingtheequationE=0.5xmxv
Momentum
a.
Momentumisapropertyofmovingobjects,itcanbedeterminedusing
theequationp=mxv
b.
Inaclosedsystem,thetotalmomentumbeforeaneventisequaltothe
totalmomentumaftertheevent.Thisistheconservationofmomentum.
Thisappliestoeventssuchascollisions
2.
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P2.3 Currents in electrical circuits
Make sure you are familiar with…
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Applying the concepts of electrical circuits to practical situation
Evaluating the use of uses of different types of lighting such as LEDs and traditional bulbs in terms of power, efficiency and cost
1.
Static electricity
a.
Insulating materials can become charged when rubbed together as electrons
aretransferredfromonematerialtotheother
b.
Thematerialthatgainselectronswillhaveanoverallnegativecharge
c.
Thematerialthatloseselectronswillhaveanoverallpositivecharge
d.
Objectsthathavethesamechargewillrepel,thosewithoppositecharges
willattract
e.
Conductors,suchasmetals,willallowchargetopassthroughthem
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2.
Electrical circuits
a.
Electric current is a movement of electrical charge
b.
I=Q/twhereIiscurrentinAmperes,QischargeinCoulombsandtis
timeinseconds
c.
Thepotentialdifferencebetweentwopointsistheenergytransferredper
Coulombofchargepassingbetweenthesetwopoints
d.
V=W/QwhereVisthepotentialdifferenceinVolts,Wistheenergy
transferredinJoules,QisthechargeinCoulombs
e.
Circuitsymbolsusedshouldbe…
f.
g.
h.
i.
j.
k.
l.
m.
n.
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p.
q.
Current-Potential Difference graphs should be drawn and interpreted
foradiode,resistorandfilamentlamp
Resistancecanbedeterminedbymeasuringthecurrentthroughand
potentialdifferenceacrossthecomponent
Currentisdirectlyproportionaltothepotentialdifferenceacrossacomponent
aslongastemperatureremainsconstant
UsetheequationV=IxR
Whencellsareconnectedinseries,thetotalpotentialdifferencetheyprovideis
thesumoftheindividualcells
Forcomponentsinseries…
a.Thetotalresistanceisthesumoftheresistanceoftheindividualcomponents
b.Thecurrentisthesamethrougheachcomponent
c.Thetotalpotentialdifferenceissharedbetweenthecomponents
Forcomponentsinparallel
a.Thepotentialdifferenceacrosseachbranchisthesame
b.Thetotalcurrentinthecircuitissplitbetweenthebranchesofthecircuit
Theresistanceofafilamentbulbwillincreaseasitstemperatureincreases
>Youshouldbeabletoexplainthisusingcollisionsbetweenionsandelectrons
Diodesonlyallowcurrenttoflowinonedirection
LightEmittingDiodes(LEDs)willemitlightwhenacurrentflows
LightDependentResistors(LDRs)decreaseinresistanceaslightintensityincreases
Thermistorsdecreaseinresistanceastheygethotter
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P2.4 Using mains electricity
Make sure you are familiar with…
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How to use mains electricity safely
Using and comparing fuses and circuit breakers
Deciding which appliances are most suitable for a particular role
1.
Household electricity
a.
Cells and batteries provide a direct current (D.C.) this always flows in the
samedirection
b.
Analternatingcurrent(A.C.)constantlychangesdirection
>Youshouldbeabletointerpretanoscilloscopedisplay
c.
MainselectricityisanA.C.supplywithafrequencyof50Hzandapotential
differenceof230V
d.
BeabletolabelandexplainthestructureofaU.K.plug
e.
Fusesandcircuitbreakersdisconnectacircuitwhenthecurrentistoohigh
f.
Fuseswillmeltandbreakwhenthecurrentthroughitishigherthanitsrating
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2.
RCCBs(residualcurrentcircuitbreakers)arefasteractingthanfuses.Theyactwhenthereisadifferenceincurrent⃝
Someappliancesdonotneedtobyearthediftheyaredoubleinsulated
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TheEarthwireprotectstheuserfromelectricshocks
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Charge, current and power
a.
When electrical charge flows through a resistor it gets hot, this may be a
wasteofenergy.Thesametakesplaceinlamps–moreefficientlamps
wastelessenergyasheat
b.
Therateofenergytransferispower–P=E/t
c.
Power,currentandpotentialdifferencearelinkedbytheequationP=IxV
d.
Energytransferred,potentialdifferenceandchargearelinkedbytheequation
E=VxQ
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P2.5 What happens when radioactive substances decay
Make sure you are familiar with…
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Explaining lifestyle factors that will affect the background radiation dose received
Evaluating the hazards of different forms of radiation
Evaluating measures to reduce exposure to radiation
Evaluating the use of radioactive sources for particular uses
Explain the results of Rutherford’s scattering experiment
1.
Atomic Structure
a.
Atoms comprise of a small central nucleus of protons and neutrons surrounded
byelectrons
b.
Protonsandneutronshavearelativeatomicmassof1,theatomicmassof
electronsisnegligible
c.
Ifanatomhasnooverallcharge,thenumberofelectronsandprotonsmust
byequal
d.
Atomsthatgainorloseelectronsarecalledionsandhaveanoverallcharge
e.
Atomsofanelementalwayshavethesamenumberofprotons;theatomic
numberisalwaysthesame
f.
Thenumberofprotonsandneutronstogetheristheatomicmass
g.
Isotopesofanelementhavethesamenumberofprotons,butcanhavea
differentnumberofneutrons
Radiation
a.
Unstableisotopesofanelementcandecaytoreleaseionisingradiation,these
aresaidtoberadioactive
b.
Thereisbackgroundradiation–youshouldbeabletodescribethesources
c.
Alphaparticlesaremadefromtwoprotonsandtwoneutrons,thisisthesame
asaHeliumnucleus
d.
Betaparticlesareelectrons
e.
Gammawavesareelectromagneticradiation
f.
Beabletowriteequationstoshowthedecayofradioactiveisotopes
g.
Beawareoftheionisingandpenetratingpowersofeachtypeofradiation
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P2.6 Nuclear fission and nuclear fusion
Make sure you are familiar with…
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The process of nuclear fission and how a chain reaction can be formed; how this can be used to generate electricity
The process of nuclear fusion and the life cycle of stars
1.
Nuclear Fission
a.
Uranium-235 and Plutonium-239 can undergo nuclear fission; most reactors use Uranium-235
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b.
Nuclearfissionisthesplittingofanatomicnucleus
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c.
Forfissiontooccur,thenucleusmustfirstabsorbaneutron
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d.
Afterfissionhasoccurred,thenucleussplitsintotwosmallernucleiandtwoorthreeneutrons;energyisreleased ⃝
e.
Theneutronsthathavebeenreleasedmaygoontocausefurthernuclearfissions
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NuclearFusion
a.
Fusionisthejoiningoftwosmallernucleitoformonelargernucleus
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b.
Fusionistheprocessbywhichenergyisreleasedinstars
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c.
Starsformfromdust,pulledtogetherthroughgravitationalattraction.Smallermassesmaybecomeplanets
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d.
Duringthe“mainsequence”,starsarestablebecausetheforcesinsidearebalanced
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e.
Astargoesthroughalifecycle.Thislifecycleisdeterminedbythesizeofthestar
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