In general, "物" means a material thing (object) while "事" means an intangible thing (event). Both of "物" and "事" can be substituted for "の" in most cases. If you just refer to a thing without paying attention to whether it is material or immaterial, "の" is a convenient term especially in colloquial expressions. In a formal occasion, we sometimes use "物事" (monogoto) to refer to a thing or collectively things that are material and immaterial.

・事 1) express a event (events). (ex : 昨日の事, event in yesterday ) 2) express a content (contents) that someone say or think. (ex : 私が思う事, what I think 彼が言った事, what he said ) ・物 express a thing (things). (ex : この部屋にある物, things in this room ) ・の substitute a noun & pronoun. (ex : 昨日食べた料理は何？ -> 昨日食べたのは何？ の substituted 料理 ) (ex : 昨日の事は忘れた. -> 昨日のは忘れた. の substituted 事 ) (ex : あなたの物です. -> あなたのです. の substituted 物 ) (ex : そこにいる人は誰？ -> そこにいるのは誰？ の substituted 人 )