力、力矩、压力测量.ppt

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1、力、力矩、压力测量7.1Introduction7.1.1Force(1)Whatistheforce?Forceisoneofthemostimportantphysicalparameters.Variousmechanicalmotionisvirtuallythetransmissionofforceortorque.Forcepossessesthecapabilityinbothstaticanddynamicphenomenon:itcanchangethebody’smotionstatusorcause

2、body’sdeformation.(2)unitofforceN(Newton):istheforcewhichwhenappliedtoamassofonekilogramgivesitanaccelerationof1m/s2.(3)Weight:istheforceexertedonabodyofmassmduetoearthgravity.G=mg;gisthelocalgravityacceleration,typicallyabout9.8m/s2.Weightmeasurementisusuallyspe

3、cifiedintermsofthemass.(4)Torque(力矩、扭矩、转矩）Torqueissometimescalledmoment.Itistheproductofaforceanditsarm.Forarotatingshaftofradiusr,thetorqueTappliedtotheshafttocauseittorotateisF×r,whereFisthetangentialforceattheradiusr.Whenashaftistwistedasaresultoftheapplicatio

4、nofatorque,shearstressesandstrainareproducedintheshaftmaterial.(5)PressureAforceFperpendiculartoanareaA,thepressurePisP=F/Aunit:Pascal(Pa)1Pa=1N/m2Atmosphericpressure:theatmospheresurroundingtheearthexertsaforceontheunitearthsurface,thatisthepressurecausedbythewe

5、ightoftheatmosphere.Itvarieswithweathercondition,theheightabovesealevel,latitude.Positivepressure:thegaugepressurehigherthantheatmosphericpressure.Gaugepressure:thepressuremeasuredrelativetotheatmosphericpressure.Thedifferentialpressurebetweentheabsolutepressure

6、andtheatmosphericpressure.Absolutepressure:usedforthepressuremeasuredrelativetozeropressure.Negativepressure:thegaugepressurelowerthantheatmosphericpressure.Vacuum:theabsolutepressurelowerthanatmosphere.7.2Measurementmethods7.2.1Forcemeasurementmethods(1)Accordin

7、gtostaticordynamiceffectStaticeffect-----thestaticforcecausesmechanicaldeformation.Bymeasuringthedeformationorusingsomeinnerstressorforcerelatedphysicaleffects.Dynamiceffect----accordingtotheNewton2ndlaw,theforceisassociatedwithacceleration.Knowingmassandaccelera

8、tionmeasured,theforcecanbedefined:F=maForcemeasurementLeverbalancemethodsBasedontheprincipleofmomentsi.e.atstaticequilibriumthealgebraicsumoftheclockwisemoment