1) WHAT IS ONE FUN THING YOU DID OVER THE SUMMER? 2) … · 2018-08-29 · SIG FIGS IN CALCULATIONS...

1)WHATISONEFUNTHINGYOUDIDOVERTHESUMMER?

2)FILLINTHEBLANK:“IWONDER(ABOUT)_____.”

WELCOME!PLEASETAKEAFEWMINUTESTOANSWERTHESEQUESTIONSONTHEINDEX CARD.YOUMAY

USETHEFRONTANDBACK.IWILLCOLLECTTHEMATTHEENDOFCLASSTODAY.

WELCOMETOGENERALPHYSICS!

GOALSFORTODAY

• Answerthequestion”Whatisphysics?”• Gooverclassroomexpectations• Introducesomebasicstophysics• Doyourfirstphysicsproblem!

WHATISPHYSICS?

• Abranchofsciencethatexploresthefundamentalprinciplesonwhichourworldisbuilt.• Physicsallowsustomakeconclusionsaboutandpredictionsofwhatwecannotseebasedonwhatwecansee.

HOWDOESPHYSICSMATTER?

• Ifyouliveinthisworld,physicsverylikelyappliestoyou!• Youwillbeabletoask,answer,andeffectivelyexplainsome(possibly

silly) questionslike:• DoesAshKetchumfromPokemon havesuperstrength?• HowmuchForcedidYodausetolifttheX-WinginEmpireStrikesBack?• Howdoyouturnarocketinspace?• Islightspeedtravelpossible?• Whydoesthemoonlookhugeandyellow-ish sometimes?• …anymanyotherquestionsyoumaywonderabout!

BASICALLY,PHYSICSWILLCHANGEHOWYOUSEETHEWORLD!GETREADYBECAUSEYOURMINDWILLBEBLOWN.

GREAT,SOHERE’SHOWTOGETTHEMOSTOUTOFTHISCLASS.

• http://robertsonphysics.weebly.com/• Mostofall,askquestionsandimagine!

THEMOSTFUNDAMENTALOFFUNDAMENTALSAREVIEWOFS.I.UNITS,SIGFIGS,ANDSCIENTIFICNOTATION

S.I.UNITS

• Length– meter(m)• Mass– kilogram(kg)• Electriccurrent– Ampere(A)• Temperature– Kelvin(K)• Time– second(s)• Andmorethatwe’llgooverlater

PREFIX SYMBOL EXPONENTIAL

Tera T 1012

Giga G 109

Mega M 106

Kilo k 103

Centi c 10-2

Milli m 10-3

Micro 𝜇 10-6

Nano n 10-9

Pico p 10-12

METRICPREFIXES

DONOTFORGETTOCONVERTTOS.I.!

CONVERTINGUNITS

• 1m=100cm=1000mm=0.001km• 100km/hr =?m/s

• 100 $%&'∗ 1000 %

$%∗ )&'*+,,-./ = 27.7778 = approx. 30m/s

• Payattentiontotheunitsintheproblemandtheunitsaskedforintheanswer.

SIGNIFICANTFIGURES

• Thenumberofreliablyknowndigitsinanumber

• Tellsyouhowaccuratelyyouknowanumber

• YoucansaydowntownLAisabout10milesawayvs.it’sexactly12.7milesaway

• Evenmoreaccurately,itmightbe12.733milesaway?

SIGFIGS

• 10hasonesigfig• 12.7hasthreesigfigs• 12.733hasfivesigfigs• 0.0067hasonly2sigfigs• Zerosareonlyplaceholderstoshowwherethedecimalis.

• Howmanysigfigsdoes80.0have?Why?• Howmanysigfigsdoes60.7have?Why?

SIGFIGSINCALCULATIONS

• MultiplyingandDividing• Theanswershouldonlyhaveasmanysigfigsasthenumberwiththeleastnumberofsigfigsusedinthecalculation.• Example– findtheareaofarectanglewithsides11.3cmand6.8cm

• Yourcalculatorwilltellyou76.84cm2,butthereisnowayyouknowtheareaofthatrectangleto0.01cm2.

• Howmanysigfigsshouldyouranswerhave?

SIGFIGSINCALCULATIONS

• Addingandsubtracting• Theanswercancontainnomoredecimalplacesthantheleastaccuratemeasurement.• Example:youtiea30.6mropetotheendofa0.57-longrope.Howlongarethetworopestogether?

• Youwillget31.17m,butroundoffto31.2m

SCIENTIFICNOTATIONANDCALCULATIONS

• Insteadofwriting1,540,000m,write1.54𝑥10+𝑚• Sidenote– howmanykmisthis?

• 1.54𝑥10+𝑚x )CD),ED

= 1.54x10*m• Insteadof0.0000448kg,write4.48𝑥10FG𝑘𝑔• Sidenote– howmanygisthis?

• 4.48𝑥10FG𝑘𝑔𝑥 ),EJ$J

= 4.48𝑥10FK𝑔

DISTANCEVS.DISPLACEMENT–YOURFIRSTPHYSICSPROBLEM

5.1km

3.6km

3.2km

Yourhouse

Coffeeshopofchoice

LCHS

Whatwasthetotaldistanceofyourtrip?

= 5.1 + 3.6 + 3.2 = 11.9𝑘𝑚

DISTANCEVS.DISPLACEMENT

5.1km

3.6km

3.2km

Yourhouse

Coffeeshopofchoice

LCHS

? km

Whatisthedistance betweenyourhouseandLCHS?

Whatisthedirection betweenyourhouseandLCHS?

3.6K + 1.9K� = 4.0706𝑘𝑚 → 4.1𝑘𝑚

𝑡𝑎𝑛F)(3.6/1.9)=62°𝐸𝑎𝑠𝑡𝑜𝑓𝑆𝑜𝑢𝑡ℎ

Yourdisplacementis4.1km62° EofS(or28°SofE)

Afteryoudoaphysicsproblem,ask– doesmyanswermakesense?

• Turntoyourpartnerandcomeupwithaonesentencedifferencebetweendistanceanddisplacement.

PointA PointB

5.1km

3.6km

3.2km

Yourhouse

Coffeeshopofchoice

LCHS

4.1km

62°

Distance=11.7km

SCALARVS.VECTOR

• Scalarshaveonlymagnitude• Distanceisascalar

• Vectorshavebothmagnitudeanddirection• Displacementisavector

SOMEPRACTICEPROBLEMS

Sallyrunstwicearounda400mtrack.Whatishertotaldistance?

a) 400mb) 800mc) 600md) Noneoftheabove

Sallyrunstwicearounda400mtrack.Whatishertotaldisplacement?a) 0mb) 800mc) 400md) Noneoftheabove

SOMEPRACTICEPROBLEMS

SOMEPRACTICEPROBLEMSBillyskateboardsfor6.7meters,thenanother0.5meteruparamp,thencoasts2.0metersbackwards.

a) DrawadiagramofBilly’smotion.

b) Whatishisdistancetraveled?

c) Whatishisdisplacement?

SOMEPRACTICEPROBLEMS

Whatis[3.0x10-3][2.0x105]?Makesuretohavethecorrect#ofsigfigs.

SOMEPRACTICEPROBLEMS

Whatis4.50x109 ?Makesuretohavethecorrect#ofsigfigs.6.636x10-5

CURBYOURINTUITION

• Establishnewpointsofreferenceforyourbrain• Importanttoevaluatewhetherornotyouranswersmakesense• Insteadofsaying“1.8m/sisabout4mph”,say“that’saboutjoggingspeed”

CURBYOURINTUITIONTemperature Length/height/distance Mass Speed

60℃ record highonearth 1cmWidthofmicroSD 3g PeanutM&M 1.4m/sWalking

45℃ HeatwaveinDubai 3.5cmlengthof 3DSgame

100gcellphone 1.8m/sJogger

35℃ Pretty grossout 12cmCDdiameter 500gBottled water 4.3m/s Bikingspeed

30℃ Beachday 75cmwidth ofCaptainAmerica’sshield

1.5kg Chromebook 11m/s SchoolZone

25℃ Roomtemp80cmdoorwaywidth 2.8kgphysicstextbook 36m/s LAdriveronfreeway

0℃ Snow 1m lightsaberblade 4kg Cat 89m/s Nascar speed

-10℃ Coldday (Moscow) 229 cmheightofYaoMIng

60kg Lady 257m/s Cruisingplane

-40℃ Spitfreezes 3m 1 storybuilding 70kg Dude 340m/s speedofsound

-50℃ lowforMinnesota 5m lengthofcar 460 kgSnorlax 3.0𝑋10a𝑚/𝑠speedoflight