Physics Notes 2023

PhysicsCheatsheet Start

1.Measurements Physical Quanitites:Quantitiesthatcanbemeasured,consistsofanumericalmagnitudeandaunit. Prefixes: GreatMajestickingsdrinkcoldmilkµntilnine Conversionof km/htom/s:km/h÷3.6=m/s Sizesof well-knownobjects:RadiusofEarth:6378000m(6.378×10 6 )Sizeofatom:0.0000000001m(10 -10 )

Vernier Calipers:Precision:0.01cmReadthemainscaleuntiltheimmediateleftofthezeromarkonthevernierscale,thenaddthemarkingwhichcoincideswiththemarkingonthemainscale.ZeroErrorsfor Vernier Calipers:Positive:ZeromarkofVernierisslightlytotherightofthemainscale.Negative:ZeromarkofVernierisslightlytotheleft. MicrometreScrewGaugePrecision:0.01mmReadmainscale,thenreadthimblereadingZeroErrors:Positive:Zeromarkingonthimblescaleisbelowdatum(centre)line.Negative:Zeromarkingonthimblescaleisabovedatumline

Pendulums:Oscillation:Onecompleteto-and-fromotion(AtoCtoA)/(BtoCtoBtoAtoB) Period:Timetakenforonecompleteoscillation PrecisionvsAccuracy:Accuracyofmeasurement Precisionofmeasurement Accuracyreferstotheclosenessofameasuredvaluetoastandardorknownvalue. Example:Youobtainamassmeasurementof3.2kgforagivensubstance,buttheactual(known)massis10kg,thenyourmeasurementisnotaccurate. Precisionreferstotheclosenessoftwoormoremeasurementstoeachother. Example:Ifyoumeasurethemassofagivensubstancefivetimes,andget3.2kgeachtime,thenyourmeasurementisveryprecise.

Errors:RandomError SystematicError ● Itoccursinallmeasurements.● Itoccurswhenanobserverestimatesthelastfigureofareadingonaninstrument. Causes:● Humanreactiontime● Backgroundnoise● Mechanicalvibrations Itcannotbepredicted. Itcanbereducedbytakingalargenumberofreadingsandaveragingthem. ● Itisnotrandombutconstant.● Itmaycauseanobservertoconsistentlyunderestimateoroverestimateareading. Causes:● Zeroerrorofaninstrument:Anyindicationthatameasuringsystemgivesafalsereadingwhenthetruevalueofameasuredquantityiszero Itcanbeeliminatedifweknowthesourcesoftheerrors.

2.Kinematics Formulas: Scalar Quantities:QuantitieswithonlymagnitudeDistance,Speed,Mass,Energy,Time Vector Quantities:QuantitieswithbothmagnitudeanddirectionDisplacement,Velocity,Acceleration,Force Distance:Totaldistancetravelled Displacement:Totaldistancetravelledinastraightline Speed:Thedistancemovedperunittime(m/s) Velocity:Therateofchangeofdisplacement(m/s) Acceleration:Therateofchangeofvelocity(m/s 2 ) *Accelerationduetofreefall:Theaccelerationduetofreefallvariesbasedonthedistancefromthecentreoftheplanet(e.g.EquatorsvsPoles,heightfromground)

3.Dynamics,MassWeightandDensity Formulas: Contact andNon-contact Forces:NormalContactForce ● Contactforce● Thepushexperiencedwhentwoobjectsarepressedtogether● Actsperpendiculartoandoutwardfromthecontactsurface Friction ● Contactforce● Opposesrelativemotionbetweentwoobjectsthatareincontactwithoneanother Tension ● Contactforce● Theforceduetoatautspring,stringorropewhichpullsontheobjectsattachedtobothitsends● Thedirectionofthisforceisalongthestring DragForce[AirResistance] ● Contactforce● Whenanobjectmovesthroughafluid(liquidorgas),thedragforceisaforcebythefluidontheobject.● Thedragforceofanobjectmovingthroughtheairisknownasairresistance.● Thedirectionofthedragforceisoppositethedirectionofthemotion(velocity)oftheobject.● Thegreaterthespeedoftheobject,thegreaterthemagnitudeofthedragforce.● Thedragforceiszerowhentheobjectisatrest Weight/GravitationalForce ● Non-contactforce● Inagravitationalfield,amassexperiencesweightduetogravitationalattraction● OnEarth,theweightofanobjectisdirectedtowardthecentreoftheEarth

ElectricForce ● Non-contactforce● Thepush(repulsion)orpull(attraction)betweenelectriccharges. MagneticForce ● Non-contactforce● Thepushorpullbetweentwomagnets,magnetsonmagneticmaterials.● Movingelectricchargesinamagneticfieldmayalsoexperienceamagneticforce. Mass:TheamountofmatterinabodyMeasuredwithabeambalancedKilograms(kg) Weight:Thegravitationalforce,orgravity,actingonanobjectMeasuredwithspringbalanceNewton(N) Gravitational Field:Aregioninwhichamassexperiencesaforceduetogravitationalattraction. Gravitational FieldStrength:Thegravitationalfieldstrength,g,isthegravitationalforceactingperunitmassonanobject.NearthesurfaceoftheEarth,g≈9.81N/kg≈10N/kg.SIunitofgravitationalfieldstrength:newtonperkilogram(N/kg)ormetrepersquaresecond(m/s 2 );1N/kg=1m/s 2 Inertia:Thereluctanceoftheobjecttochangeitsstateofmotionduetoitsmass. Vector Diagrams:Inavectordiagram,ifall3arrowsformacompleteloop,theforcesareinequilibrium ParallelogramMethod:

TiptoTail Method: Newton’sLawof Motion:1. 1st Law:Intheabsenceofanetforceactingonitastationaryobjectremainsstationary,whereasamovingobjectcontinuesmovingatconstantspeedinthesamedirection.2. 2ndLaw:Whenanetforce,Fnet,actsonanobjectofaconstantmass,thedirectionoftheaccelerationoftheobjectisthesameasthedirectionofthenetforce.Theproductofthemassandaccelerationoftheobjectgivestheresultantforce.3. 3rdLaw:Foreveryaction,thereisanequalandoppositereaction.● Ifoneobjectexertsaforceonasecondobject,thesecondobjectexertsaforceonthefirstobject.Thesetwoforceshaveequalmagnitudesandoppositedirections. FreeBodyDiagram: Friction:Frictionisacontactforcethatopposesrelativemotionbetweentwoobjectsthatareincontactwithoneanother.Frictionistheresultofirregularitiesofthesurfacesthatareincontact.

PositiveandNegativeEffectsof Friction:PositiveEffectsofFriction NegativeEffectsofFriction (a)Preventsfoodfromslippingwhengrippingfoodbetweenchopsticks (b)Frictionbythebrakepadsonbicycletyresdecreasesthespeedofabicycle (c)Frictionbetweenrubbertiresandtarroadsallowscartogriptheroadsproperly.● Toenhancethispositiveeffect,cartyreshavegroovesthatchannelwaterunderthetyreaway.Thishelpspreventskidding.(d)Rockclimbersusechalkpowderthatabsorbssweatontheirpalms.Thisimprovestheirgripoftherocksurface. (e)Rubbingofhandsduringcoldweatherorrubbingtwopiecesofwoodtostartafire. (a)Whenenginesoperate,frictioncausessomeinputenergytobeconvertedintosoundorthermalenergy.Theusefuloutputenergyislessthanthetotalinputenergy.Overheatingmaybedangerous. (b)Causeswearandtearofmovingpartsofshoes,engines,motorsandmachines. ReducingtheNegativeEffectsofFriction (a)Polishingsurfacestomakethemsmoothreducesfriction,e.g.thepistonsandcylindersofanenginearemadeofhighlypolishedsteeloraluminium (b)Lubricantslikeoilorgreaseareappliedtomovingpartstopreventwearandtear.Theyhelpsmoothoversurfaceirregularities. (c)Ballbearingsplacedbetweentwomovingpartsensurethemachinesdonotrubagainsteachother.Theycanbefoundinthewheelsofcars,bicycles,skates. (d)Thelayerofairinanaircushionbetweenmovingsurfacesreducesfriction,e.g.hovercraftsandmagneticlevitation(Maglev)trainsfloatslightlyabovethesurfacesothattheycanmovefaster.