collision

Explanation

Thephenomenonthattwoobjectsinrelativemotioncontactandquicklychangetheirmotionstate.Itcanbethecollisionofmacroscopicobjects,suchastamping,forging,hittingtheball,etc.,orthecollisionofmicroscopicparticlessuchasatoms,nuclei,andsubatomicparticles.Inclassicalmechanics,thedirectcollisionoftwoballsisusuallystudied,thatis,therelativespeedisexactlyonthelineofthecenterofthesphere.Becausethecollisionprocessisveryshort,theimpulsebetweenthecollidingobjectsisfargreaterthantheforcegiventothembythesurroundingobjects,andtheeffectofthelattercanbeignored.Thesystemcomposedofthesetwoobjectscanberegardedasanisolatedsystem.Momentumandenergyareconserved,butmechanicalenergyisnotnecessarilyconserved.Iftheelasticityofthetwoballsisverygood,thepotentialenergystoredduetodeformationduringthecollisioncanbecompletelyconvertedintokineticenergyduringseparation,andthereisnolossofmechanicalenergy.Itiscalledacompletelyelasticcollision,andthecollisionofthesteelballisclosetothissituation.Ifitisacollisionbetweenplasticballs,thedeformationcannotberecoveredatall.Afterthecollision,thetwoballsmoveatthesamespeed,andalargepartofthemechanicalenergyisconvertedintointernalenergythroughinternalfriction.Thisiscalledacompletelyinelasticcollision,suchasthecollisionofamudballorawaxball.Impactpendulumalsobelongstothiscategory.Theonebetweenthetwo,thatis,thetwoballsonlypartiallyreturntotheiroriginalstatewhentheyareseparated,whichiscalledanincompleteelasticcollision,andthelossofmechanicalenergyisbetweentheabovetwotypesofcollisions.Collisionbetweenmicroscopicparticles,suchasonlytheexchangeofkineticenergywithoutchangesinthetype,numberorinternalmotionstateoftheparticles,iscalledelasticcollisionorelasticscattering;suchasnotonlytheexchangeofkineticenergy,butalsothetransitionofparticleenergystateorthegenerationofparticlesAndannihilationiscalledinelasticcollisionorinelasticscattering.Inparticlephysics,informationabouttheinteractionbetweenparticlescanbeobtained,whichisaveryimportantresearchtopic.

Thecollisionprocesstimeisextremelyshort,sotheinternalforceisalwaysgreaterthantheexternalforce,andthemomentummustbeconserved.

(1)Collisionisgenerallydividedintotwoprocesses:compressionphaseandrecoveryphase.

(2)Collisioncanbedividedintothefollowingcategories:completelyelasticcollision,completelyinelasticcollisionandincompleteelasticcollision.

Energyconversionincollision

Inthecompressionphase,thekineticenergyoftheobjectisconvertedintootherformsofenergy,andintherecoveryphase,otherformsofenergyareconvertedintokineticenergy.

Inafullyelasticcollision,thetotalkineticenergydoesnotchangebeforeandafterthecollision.

Collisionisclassifiedbyenergyangle

Idealelasticcollision

Whentwoobjectscollidewitheachother,theenergyisnotconvertedintointernalenergy(suchasheatordeformation).Accordingtothefirstlawofthermodynamics,thesumofkineticenergybeforecollisionisequaltothesumofkineticenergyaftercollision.Inthelawofconservationofmomentum,thesumofmomentum(vector)beforecollisionisalsoequaltothesumofmomentumaftercollision.

Theidealelasticcollisionisaphysicalmodelinthemacroscopicview.Duetofrictionandotherfactors,thesystemalwaysloseskineticenergy.Relatedmodelssuchasbilliardballsandrubberballs.

Inthecollisionbetweenatomsandelementaryparticles,thereisaminimumenergyaccordingtoquantummechanics.Thisminimumenergyprovidesimpetusforatomsorotherparticles,orprovidesnecessaryconditionsforcreatingandtransformingparticlesinquantumphysics.Thisenergyisstillnotenoughforanidealelasticcollision.

Accordingtothefirstlawofthermodynamics,thesumofmomentumbeforeandafterthecollisionmustbeequal.

Thedirectionofmomentumcannotbeignored,becausethevectorsumisalargevalueinn-dimensionalspace(n>1).Thesquareofthevectorisregardedasascalarinthelawofconservationofenergy.Therefore,pleasenotethatthevelocityandthecollisiondirectioninthefollowingformulaarethesame(tangent),ratherthanintersecting.

Inthetwo-dimensionalormulti-dimensionalspace,thecollisionmustbedisassembledandanalyzedbasedonthecollisionangle.

Inelasticcollision

In"inelasticcollision",partofthekineticenergyisconvertedintointernalenergy(U).Whenanobjectdeformsorheatsupinacollision,thecollisioniscalled"inelastic."Inelasticcollisionssatisfytheconservationofmomentum,butnottheconservationofmechanicalenergy(partiallyconvertedintointernalenergy).

Completelyinelasticcollision

Inacompletelyinelasticcollision,thereisnoreboundatallafterthecollision,andasmuchkineticenergyaspossibleispartiallyconvertedintointernalenergy,thenthekineticenergyinthiscollisionsystemThebiggestloss.Therefore,thetwosubstances"stick"togetherafterthecollisionandcontinuetoflyatthesamespeed.Forexample,twoplasticineballssticktoeachotheraftercollisionandcontinuetomoveatthesamespeed.

Superelasticcollision

Inasuperelasticcollision,theinternalenergytransformsmorethanthekineticenergyofatleastonecollider.Itskineticenergyafterthecollisionisgreaterthanitskineticenergybeforethecollision.Themathematicalexpressionisthesameasthegeneraldescriptionofinelasticcollision,whichisU<0.

Collisionisclassifiedbycollisionangle

Directimpact(directimpact)

Amovingballcollideswithastationaryball.Thespeedoftheballbeforethecollisionisonthesamelineasthelineconnectingthecentersofthetwoballs.Afterthecollision,thespeedofthetwoballswillstillfollowthisline.Thiskindofcollisioniscalledpositivecollision,alsocalledcentercollision.

Obliqueimpact(obliqueimpact)

Ifamovingballcollideswithastationaryball,ifthespeedoftheballbeforethecollisionisnotonthesamelineasthelineconnectingthecentersofthetwoballs,Afterthecollision,thespeedofthetwoballswilldeviatefromtheoriginallineofthecentersofthetwoballs.Thiscollisioniscalledobliquecollision,alsocalledoff-centercollision.

Thecollisionofanobjectagainstanobstacle

Thecollisionofanobjectagainstafixedobjectsuchasthegroundorawallbelongstothistype,anditcanalsobedividedintoafrontalcollisionandanobliquecollision.

Collisionoftheobjecttotherotatableobject

WhentheobjectAcollideswiththeobjectBthatcanrotatearoundtheOaxis,theobjectBsuddenlyacquiresanangularvelocitychange(Figure4).Generally,acollisionreactionforceisimmediatelygeneratedatthesupportOofB,anditsmagnitudeisrelatedtothepositionofthecollisionaction,thatis,thedistanceOO₁.However,underspecialconditions,althoughthesuspendedobjectissubjecttoimpact,itsbindingforcecanstillbezero.

Othertypesofcollisions

Scattering

Inparticlephysics,atomicphysics,orwhenaphotonisusedasoneofthecollisionobjects,collisionisalsocalledscattering,dissipationordiffusion.Whenaparticletransitionstoanotherenergylevelinacollision,itisalsocalledaninelasticcollision(inelasticscattering).Whenmostphotonsparticipateinaninelasticscattering,theirtotalwavelengthwillchange.ForrelatedpleaserefertoScatteringandScatteringPrinciples.

Reactioncollision

Reactioncollisioncomesfromreaction,suchaschemicalreactionorthecollisionofhigh-energyparticlesinquantumphysicstoproducenewparticles.Itmustbenotedherethatdifferentparticlesbeforeandafterthecollisionprovideenergyandmomentum.Duringthecollision,thespeedchangesatthesametimetherearechangesinthemassandquantityofparticles.

Atypeofreactioncollisionsuchas"electronegativeexchange":theatomicphysicsprocessoftheexchangeofoneatom,moleculeorion,oneormoreelectrons.Itispossiblethatduringthisprocessanelectrongivespositivechargetooneofthecollisionobjects.Forexample,positronsinthesolarwind(seehigh-energyions)arecapturedandemitx-rayswhentheypassthroughtheatmospherearoundthecomet.

Applicationofcollision

Usethehugecollisionforcegeneratedduringcollisiontogeneratehugeinstantaneousforce,suchasvariouspunchingmachines,piledrivers,shellpiercing,etc.Onthecontrary,sometimestoavoidthehazardofhugecollisionforce,variousbufferdevices,suchaselasticbodiesorhydraulicshockabsorbers,areusedtoprolongthecollisiontimeandreducethecollisionforce.Collisionhasbecomeanimportantmechanicalprobleminmodernengineeringtechnology.Thehugecollisionforceandcontinuouscollisionhaveagreatinfluenceonthestrengthandfatigueofthematerial.Inaddition,instruments,devicesandequipmentshouldensurethattheycanworknormallywhentheircarriersaresubjectedtocollisionsandimpactloads,withoutloosening,malfunctioningordamage.

References

1.Theauthoroftheentry:GaoWeibing."ChinaEncyclopedia"Volume74(FirstEdition)MechanicsEntry:Collision:ChinaEncyclopediaPublishingHouse,1987:379-380pages.