01Units physical0213.docx
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01Unitsphysical0213
Units,physicalfundamentalterms
Whenmeasuringitiscomparedwithfixedmeasuringunits.
Lengthsaremeasuredwithameteringruleincentimetresandmillimetre,unitsofweightwithascaleinkilogrammesandgrammes,timeismeasuredwithaclockinhoursandminutesandtemperatureismeasuredwithathermometerindegrees.
Theseunitsaredefinedinthe“internationalunitsystem”（SI）.
Thefollowingbasicunitshavearelevanceformechanicalmeasurements:
∙meter（m）forthelength,
∙kilogramme（kg）fortheweight,
∙second（s）forthetime.
Furthermore,therearebasicunitsforelectricalamperage（Ampere）,voltage（Volt）,temperature（Kelvin）andforintensityoflight光强（Candela烛点）.
Furthermeasuringunitscanbederivedfromthebasicunits.
Theseareeitherdecimalunitsorlargerunits,e.g.
∙decimetre公寸,millimetre毫米,kilometreetc.
∙gramme克,tonneetc.
∙minute,houretc.
Lengthunits
Meter（m）isthebasiclengthunit.
1m=10dm=100cm=1000mm=1000000µm（micrometer）
InchesareusedinGreatBritainandtheUSA.
1Inch=25,4mm
Weightunits
Kilogramme（kg）istheunitofweight.
1kg=1000g
Newton（N）istheunitofgravity重力.
1N=0,1kg
SI-Basicunits
Terms
Symbol
Unit
Comments
Terms
Symbol
Unit
Comments
Name
Abbreviation
Name
Abbreviation
Length长度
L
Metre
m
Torque
M
Newtonmetre
Nm
M=Fl
Width宽
B
Mass质量
m
Kilogramme
kg
1kg=1000g
Height,depth高，深
H
Weight重量
Gramme
g
Radius半径
R
Tonne
t
1t=1000kg
Diametre直径
D
Temperature
T
Kelvin
K
0K=-273°C
Distance距离
S
t
Celsius
°C
0°C=273K
Area
A
Squaremetre
m²
Capacity功率
P
Watt
W
kW
Time
T
Second
s
Pressure
p
Pascal
Pa
100000Pa=
Periode
Minute
min
1min=60s
bar
1bar
Hour
h
1h=60min
Electrical
voltage
U
Volt
V
U=RI
Duration
Day
d
1d=24h
Year
a
Electrical
current
I
Ampère
A
Velocity速度
V
Metre/second
m/s
1m/s=
3,6km/h
Electrical
resistance
R
Ohm
Ω
Kilometre/Hour
km/h
Accelaration
A
Square
Metre/second
m/s²
Work做功
W
Joule
J
Accelerationoffall
G
m/s²
9,81m/s²
Energy能量
E,W
1J=1Ws
=1Nm
Force力
F
Newton
N
F=ma
Gravity重力
G
G=mg
Multipleandpartsofunits
Task:
Enterthederiveddecimalorthemultipleunitsinthechartbelow!
Name
Symbol
Factor
Example
Task
Giga十亿
G
1000000000
1GW=1000000000W
0,02GW兆瓦=
20000kW
Mega百万
M
1000000
1MW=1000000W
50MW=
50000kW
Kilo千
k
1000
1kN=1000N
350N=
0,35kN
Hecto百
h
100
1hPa=100Pa
5500Pa=
55hPa
Deca十
da
10
1daN=10N
1000daN=
10000N
Deci
d
0,1
1dm=0,1m
600m=
6000dm
Centi
c
0,01
1cm=0,01m
253m=
25300cm
Milli
m
0,001
1mm=0,001m
563mV=
0,563V
Micro
µ
0,000001
1µm=0,000001m
20cm=
200000µm
Nano
n
0,000000001
1nm=0,000000001m
33nm=
0,0000033cm
Forces
Differentforcesaremadeuseofinthemechanics机械学.
Theoldestforceistheuseofhumanandanimalmuscularstrength.Todaymuscularstrengthstillplaysanimportantrolealthoughbymoderntechnologymachinesarereplacingitmoreandmore.
Ifaforceoperatesonanobject,itcaneithercauseadeformation,accelerationoranequalcounterpoise平衡of/totheobject.
AT_00_0056
AT_00_0054
Force=mass×accelerationF=m×a
ThederivedSI-unitofforceisNewton（N）.
Ontheearth’ssurfacedominatesanaccelerationforceofa=9,81m/s2.重力加速度
Aforceisclearlydefinedby
pointofapplication-size–directionofthelineofaction.
Theforceisshownbyadrawnarrow.Thedimensionoftheforceresultsfromthelengthofthearrowaccordingtothechosenforcemeasuringunit.
Shouldaforcebetransferredanddistributedintwodirectionsthedimensionofthepartialforcescanalsobedeterminedbytheuseoftheparallelogram平行四边形offorces.
力的定义
力是物体之间的相互作用，能使物体的运动状态发生改变，或使物体变形。
在理论力学中讨论的主要对象为质点或刚体，则力的作用效果只改变其运动状态。
在国际单位制中，力的单位为kg∙m/s2，或称为牛顿（N）。
AT_00_0055
LeverandTorque
Theleverpossessestwoleverarmswithacommonpivot支点.Ifthepivotalpointissituated位于betweenthetwoforcesthenitconcernsadouble-sidedlever.
Theturningpoint受力点ofaonesidedleverliesattheendofthelever.
Atorqueisbeingproducedonbothleverarmsbybothforces.
Aleverisbalancedwhentheanticlockwisemoment力矩isequaltotheclockwisemoment.
Inphysicseverybodyiscalledleveronwhichaforcecausesarotatingactione.g.crowbars撬棍,pliersandtoothedwheels.Therotatingactioniscalledtorque.
Thetorquegrowswiththeincreasingforceandthelengthoftheleverarm.
AT_00_0052
AT_00_0053
Torque=force×leverarmM=F×r
Thenewtonmetre（Nm）isthederivedSI-unitofthetorque.
Thepropertiesoftorquesappear扭矩产生的情况e.g.whilsttighteningascrewwithaspanneraswellasoncrankshafts,handwheels方向盘,toothedwheelsetc.Theforcealwaysoperatesonaleverarm.Thisistheeffectiveradiusonrotaryobjects.
M=r×F
改变匀速定轴转动的运动状态的作用就是力矩，作用力作用于转动物体，从而改变它的转动状态，是通过力矩的形式进行的。
AT_00_0051
Task:
Whichtorqueactsuponthescrew?
80N0,25m=20Nm
Energy,Work
Inpowermachines,theinputenergyistransformedintoaformofenergythatisnecessaryforacertainfunctionofthemachine.
Thecombustionengineisapowermachineinwhichthechemicalenergyofthefuelisbeingtransformedintokineticenergy（内燃机是一个做功机械将化学能转为动能）whichisneededforthedriveofthevehicle.
Mechanicalworkisperformedwhenabodyundertheinfluenceofaforceputsawaybacktotheforcedirection.
在我们周围的环境中，我们接触的都是一些彼此之间以某种力（弹性力、万有引力、摩擦力以及其他各种力）互相作用着的物体．所以，在这种情况下，物体的位置改变，只有在力的作用下才能实现．因此，自然就有表明力使物体移动的作用特性的必要性．在力学中，作为这种特性，所取的是这样一个量：
沿移动方向的分力和这分力的作用点移动的距离愈大，这个量也愈大．这个量叫做功．”这一段话的前一半说明功的概念是如何产生的．它包含着两个重要因素：
其一就是物体与物体之间的相互作用；其二就是在相互作用之下物体位置改变的过程所具有的一个共同的特性，这一特性就是功．即
，其中s表示力的作用点移动的距离（即移位的大小），
表示力在位移方向的分力
AT_00_0062.1
Mechanicalwork（w）grows
withthesizeoftheforce（F）andW=F×s
withthelengthofthedistance（s）.
ThederivativeSI-unitformechanicalworkisthenewtonmetre（Nm）orjoule焦耳（j）andalsowattsecond瓦（ws）.
1newtonmetreisthemechanicalworkwhichisperformedwhenthepointofapplicationoftheforceof1nisdisplacedby1minthedirectionoftheforce.
Typesofmechanicalwork:
1瓦等于1N力使物体移动一米（物体延作用力方向）
∙Liftingwork=weightforce×liftingheight,
∙Brakingwork=brakingforce×brakingdistance,
∙Accelerationwork=accelerationforce×accelerationdistance.
∙1马力=0。
735千瓦
Thesameworkcanbeeitherperformedwithalargerforceatshortdistanceorwithasmallforceatlongdistance.
Forthispurpose,anapplianceisneededtoallow“Savingforceattheexpenseofthedistance“.Thereby,thegivenworkcanneverbelargerthantheusedwork.
Aconversion转换offorce,whichisalsocalledaconversionoftorquecanresultfromtheaccordingleverage杠杆原理.杠杆
定义：
一根硬棒，在力的作用下如果能绕着固定点转动，这根硬棒就叫做杠杆。
Inanautomobilethisisachievedbythetransmissionoftoothedwheelsorbelts.
Thehighertorqueisoperatingonthebiggertoothedwheel（biggerleverarm,moreteeth）atatoothedwheelpairing.
Theleveragecorrespondstotheproportionofteethofthedriventoothedwheeltothedrivingcogwheel.
AT_00_0060.1
AT_00_0060.2
AT_00_0060.3
Transmissionratio（i）istheproportion
ofthetorqueofthedrivenwheel（M2）
tothetorqueofthedrivingwheel（M1）.
i=transmissionratio
Drivingtoothedwheel=unevennumbers
Driventoothedwheel=evennumbers
Ifthedistributionforceinagearunitorabeltdrive,e.g.liesovertwotoothedwheelpairs,theyresultintwopartialtransmissions.
AT_00_0050.1
icomplete=i1×i2
Capacity,Efficiencyfactor
Inmachines,theenergyistransformedandmadeuseful.
Energylossesoccurwitheveryenergytransformation,whichiscausedbyfriction,heatabstraction热损失,andthermalradiation热辐射.
Theresultisthattheoutputcapacityofamachineisalwayssmallerthantheinputcapacity.
Tocomparethemachinestotheircapability,thefollowingefficiencyfactorisused（eta）.
AT_00_0066
Efficiencyfactor效率istheproportionofoutputcapacityPouttoinputcapacityPin.
total=1×2×3×....
1.Pin=Inputcapacity;2.PV=Losscapacity
3.Pout=Outputcapacity
Astheoutputcapacityisalwayssmallerthantheinputcapacity,theefficiencyfactorisalwayslowerthan1orlowerthan100%.Theinputcapacityalwaysequalsto100%.
Theefficiencyfactorofelectricalmachinesisthebestwhereastheworstefficiencyfactorisinheatenginese.g.gasolineanddieselengines.
Forcomparison
Efficiencyfactorgasolineengineapprox.35%resp.0,35
Efficiencyfactordieselengineapprox.45%resp.0,45
Efficiencyfactorelectricalmotorapprox.90%resp.0,9
AT_00_0065
total=0.3*0.95*0.9*0.9=0.231
Duringthecombustionoffuelintheengine,onlyasmallpartoftheproducedenergyistransformedintoeffectivepowerthatispassedontothegearbox.
Thelargestpartoftheenergycannotbeusedforthepowerengine.
Task:
Thecirculardiagrambesidesshowstheenergydistributionforagasolineengine.Completethetable!
Inserttheacquiredvaluefortheeffectivepowerinthetable!
Completethecirculardiagramwiththecalculatedpercentagefortheusability.
Radiantheat热辐射
4%
Friction,auxiliarydrive摩擦损失
6%
Effectivepower有效
34%
Exhaustheat排气热量
35%
Coolantheat冷却热量
21%
Tasksconcerningtransformation:
1.Toothedwheeldrive:
Themissingvaluesaretobe
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