初中物理單位及公式

初中物理單位及公式

A,density(P):

1.Definition:themassofasubstanceinaunitvolumeiscalled

thedensityofsuchasubstance.

2,theformula:P=m/vv=m/Pm=VP:deformation

Mforobjectquality,themainunitkg,commonlyusedunits:

T,G,mg;

Visthevolumeofanobject,themainunitcm3,M3

3,unit:internationalunitsystem:kg/m3commonunitg/cm3

unitconversionrelationship:1g/cm3=103kg/m3

Thedensityof1kg/m3=10-3g/cm3wateris1*103kg/m3andreads

1*103kgpercubicmeter,whichmeansthatthephysicalmeaning

is1cubicmetersofwaterwithamassof1*103kg.

Two,speed(V):

1.Definition:inuniformrectilinearmotion,velocityisequal

tothedistancetraveledbyamovingobjectinunittime.

Physicalmeaning:velocityisthephysicalquantitythat

indicatesthespeedofanobject

2,formula:v=s/tdeformation:s=vtt=s/v

Sfortheobjectofthejourney,thecommonlyusedunitsfor

KMm;tfortheobjectusedbythetime,commonlyusedunits

forSH

3,units:internationalsystemofunits:m/scommonlyused

unitskm/hconversion:Im/s=3.6km/h.

Three,gravity(G):

1.Definition:theforcenearthegroundduetotheattraction

oftheearthiscalledgravity

2.Formula:G=mg

Misthephysicalmass;Gisthecoefficientofgravity,g=9.8N,

/kg,roughlyg=10N/kg

3units:Newtonreferredtoascattle,expressedinN

Fourleverprinciple

1.Definition:thebalanceconditionofleverispower*power

arm=resistance*resistancearm

2,formula:F1*11=F2*12canalsobewrittenas:Fl/F2=12/

LI

Amongthem,Flistheforcethatmakestheleverrotate,namely

power;LIisthedistancefromthefulcrumtothedynamicaction

line,thatis,thedynamicarm;

F2istheforcethatblockstherotationofthelever,thatis,

resistance;L2isthedistancefromthefulcrumtothelineof

resistance,thatis,theresistancearm

Five,pressure(P):

1.Definition:thepressureonaunitareaofanobjectiscalled

pressure.

Physicalmeaning:pressureisthephysicalquantitythat

indicatestheeffectofpressure.

2.Formula:P=F/S

Fisthepressure,thecommonunitNewton(N);theSistheforce

area,andthecommonlyusedunitism2(M2)

3,theunitis:Pascal(Pa)

Six,liquidpressure(P):

Formula:P=1,PGH

Wherepisthedensityofliquid,commonlyusedkg/m3g/cm3;

Ggravitycoefficient,g=9.8N/kg;

Hisdepth,commonlyusedinunitsm,CM

2,theunitis:Pascal(Pa)

Seven,Archimedesprincipleforbuoyancy

1content:theobjectimmersedintheliquidisupwardbuoyancy,

thesizeofbuoyancyisequaltothegravityoftheliquidit

discharges

2Formula:F=G=PliquidfloatingrowrowgV

TheGisusedtoholdthegravityoftheliquid,commonlyused

asN;

ThedensityofliquidliquidinfiltrationforPobjects,

commonlyusedkg/m3g/cm3;

Vrowsofliquidvolume,commonlyusedunitcm3m3;Gisthe

coefficientofgravity,g=9.8N/kg

3units:cattle(N)

Eight,merit(W):

1,thedefinition:distanceproductthroughworkisequalto

forcewiththeobjectinthedirectionoftheforce.

2.Formula:W=FS

Amongthem,Fistheforceoftheobject,thecommonlyusedunit

forthecattle(N);

Sisthedistancepassedinthedirectionofforce,andthe

commonunitism

3units:Joule,1J=1N,M

Nine,mechanicalefficiency(ETA):

1,thedefinition:withtheratioofhardwork

2,theformula:ETA=W/Wtotaluseful

Wusefulworkisusefulforpeople,thatis,workhard;

Wisusefulwithextraworkorpowerwork,namelythetotalwork.

Theunitsarejoules(J)

3.Unit:usuallyexpressedasapercentage(%)

Ten,power(P):

1.Definition:theworkdoneinunittime.

Physicalmeaning:theamountofphysicalforceindicatingthe

speedatwhichworkisdone.

2Formula:P=W/t

Wfortheworkdone,unitJoule(J);tisthetimetodowork,

unitsh

3,units:mainunitW;commonunitskWconversion:lkW=103W,

lmW=106,W

ElevenOhm'slaw

1.I=U/R(Ohm'sLaw:theelectriccurrentinaconductoris

proportionaltothevoltageattheendofaconductorand

inverselyproportionaltotheresistanceofaconductor)

2.I=I1=I2=...=In(thecharacteristicsofcurrentinaseries

circuit:currentsareequaleverywhere)

3.U=U1+U2+…+Un(voltagecharacteristicinseriescircuit:

inseriescircuit,thetotalvoltageisequaltothesumofthe

voltageateachendofeachcircuit)

4.I=I1+I2+...+In(features:parallelcurrentcircuitofthe

currentlineisequaltothecurrentofeachbranchand)

5.U=U1=U2=...Voltagecharacteristicof=Un(parallelcircuit):

thevoltageacrosseachbranchisequal.Equaltothepower

supplyvoltage)

6.R=R1+R2+...+Rncharacteristicsofresistorsinseries

circuits:thetotalresistanceequalsthesumofthe

resistancesofeachpartofthecircuit

7.1/R=1/R1+1/R2+...Characteristicsofresistorsinparallel

circuits(+1/Rn:thereciprocalofthetotalresistanceis

equaltothesumofthereciprocalresistancesofeachshunt

resistor)

8.R==R/n(theformulaoftotalresistancewhenNparallel

resistorsareconnectedinparallel)

Formulafortotalresistanceof9.Rseries=nR(nresistorsin

series)

10.UI:U2=R1:R2(voltageandresistanceinaseriescircuit:the

ratioofvoltageisequaltotheratiooftheirresistance)

11.Il:I2=R2:RI(therelationbetweencurrentandresistancein

parallelcircuits:theratioofcurrentsisequaltotheinverse

oftheircorrespondingresistance)

Twelve,electricalpower,powerpart

12.P=UI(empirical,suitableforanycircuit)

13.P=W/1(definition,suitableforanycircuit)

14.Q=I*2Rt(Joule'slaw,suitableforanycircuit)

15.P=P1+P2+...+Pn(suitableforanycircuit)

16.W=UIt(empirical,suitableforanycircuit)

17.P=I*2R(compoundformula,onlyforpureresistancecircuit)

18.P=U2/R(compoundformula,onlyforpureresistance

circuit)

19.W=Q(empiricaltypeonlyforpureresistancecircuit).W

istheworkdonebythecurrentflowingthroughtheconductor,

andQistheheatproducedbythecurrentflowingthroughthe

conductor

20.W=I"2Rt(compoundformula,onlyforpureresistance

circuit)

21.W=U*2t/R(compoundformula,onlyforpureresistance

circuit)

22.Pl:P2=U1:U2=R1:R2(inseriescircuits,therelationbetween

electricalpowerandvoltage,resistance):theratioofthe

electricpowerintheseriescircuitisequaltotheratioof

theirvoltagetoresistance

23.Pl:P2=I1:I2=R2:R1(therelationbetweenelectricalpower

andcurrent,resistanceinparallelcircuits:inparallel

circuits,theratioofelectricalpowerisequaltotheir

currentratio,equaltotheirinverseresistance)

TheresultantforceisthesameasF(N):Fand=F1+F2

Intheoppositedirection:whenFisinoppositionto=F1-F2,

F1>F2

Buoyancy,F,floating(N)F,floating,=G,-G,G,dependingon

thegravityoftheobjectintheliquid

BuoyancyFfloating(N)Ffloating=Gmatter-thisformula

appliesonlytoobjectsfloatingorsuspended

F(N)Fbuoyancyfloatfloat=Gg=PgV=mrowrowrowliquid

PlatoonG:thegravityoftheliquid

PlatoonM:thequalityoftheliquid

P:liquidliquiddensity

RowV:thevolumeoftheliquidthatisdischarged(thevolume

oftheliquidimmersedinit)

FixedpulleyF=G

S=h

F:thepullofthefreeendoftherope

G:gravityofobjects

S:thedistanceatwhicht