Capillaryforcesaresignificantlydominantinadhesiveforcesmeasuredwithanatomicforcemicroscope(AFM)inambientair,whicharealwaysthoughttobedependentonwaterfilmthickness,relativehumidity,andthefreeenergyofwaterfilm.Westudythenatureofthepull-offforceonavarietyofsurfacesasafunctionoftipvelocity.Itisfoundthatthecapillaryforcesareofrelativelystrongdependenceontipvelocity.ThepresentexperimentisexpectedtoprovideabetterunderstandingoftheworkmechanismofAFMinambientair.