受力分析和受力图BasiccForceanalysisandforcediagramonceptsofstatics主讲人：申潇

123目录CONTENTS约束和约束力受力分析和受力图例题解析ConstraintsandBindingForcesForceanalysisandforcediagramExampleanalysis

1约束和约束力ConstraintsandBindingForcesONE

一、约束和约束力ConstraintsandBindingForces1.基本概念Basicconcepts●自由体:在空间能向一切方向自由运动的物体。Freebody:anobjectthatcanmovefreelyinalldirectionsinspace.●非自由体:不可能产生某方向的位移的物体。Nonfreebody:anobjectthatcannotproducedisplacementinacertaindirection.●约束:由周围物体所构成的、限制非自由体位移的条件。Constraints:Conditionsformedbysurroundingobjectsthatrestrictthedisplacementofnonfreebodies.●约束力:约束施加于被约束物体上的力。Constraint:Constrainstheforceappliedtotheconstrainedobject.●主动力:约束力以外的力。Activeforce:aforcebeyondtheconstraintforce.

一、约束和约束力ConstraintsandBindingForces约束constraint约束力FtBindingforceFt被约束物体一一非自由体Constrainedobject-nonfreebody主动力PActiveforceP

工程中常见的约束Commonconstraintsinengineering柔体约束Softbodyconstraints绳子、链条、皮带等并不是理想化的柔索，但可简化成这种约束。Ropes,chains,belts,etc.arenotidealizedflexiblecables,butcanbesimplifiedintosuchconstraints.一、约束和约束力Coupleofforces柔绳约束实例Exampleofflexibleropeconstraint

皮带约束实例Beltconstraintinstance一、约束和约束力Coupleofforces

一、约束和约束力ConstraintsandBindingForces理想刚性约束:当物体变形可以忽略时，约束与被约束体之间的接触可假设为刚性。Idealrigidconstraint:Whenthedeformationofanobjectcanbeignored,thecontactbetweentheconstraintandtheconstrainedbodycanbeassumedtoberigid.

一、约束和约束力ConstraintsandBindingForces(2)光滑面约束Smoothsurfaceconstraint当物体与固定约束或活动约束间的接触表面非常光滑，摩擦可以忽略不计时，就可简化为光滑面约束。Whenthecontactsurfacebetweenanobjectandafixedoractiveconstraintisverysmooth,frictioncanbeignoredandsimplifiedasasmoothsurfaceconstraint.阻碍物体沿两接触面法线n方向往约束内部的运动，不能阻碍沿切线τ方向的运动。Obstaclethemovementofanobjecttowardstheinterioroftheconstraintalongthenormalndirectionofthetwocontactsurfaces,butnotalongthetangentlineτMovementindirection.

(2)光滑面约束Smoothsurfaceconstraint光滑面约束力一一法向力