Gravitation,orgravity,isanaturalphenomenonbywhichphysicalbodiesattractwithaforceproportionaltotheirmass.Gravitationismostfamiliarastheagentthatgivesweighttoobjectswithmassandcausesthemtofalltothegroundwhendropped.Gravitationcausesdispersedmattertocoalesce,andcoalescedmattertoremainintact,thusaccountingfortheexistenceoftheEarth,theSun,andmostofthemacroscopicobjectsintheuniverse.

　　GravitationisresponsibleforkeepingtheEarthandtheotherplanetsintheirorbitsaroundtheSun;forkeepingtheMooninitsorbitaroundtheEarth;fortheformationoftides;fornaturalconvection,bywhichfluidflowoccursundertheinfluenceofadensitygradientandgravity;forheatingtheinteriorsofformingstarsandplanetstoveryhightemperatures;andforvariousotherphenomenaobservedonEarth.

　　Gravitationisoneofthefourfundamentalinteractionsofnature,alongwithelectromagnetism,andthenuclearstrongforceandweakforce.ModernphysicsdescribesgravitationusingthegeneraltheoryofrelativitybyEinstein,inwhichitisaconsequenceofthecurvatureofspacetimegoverningthemotionofinertialobjects.ThesimplerNewton'slawofuniversalgravitationprovidesanaccurateapproximationformostphysicalsituations.