In Grammar, passed is adjective, past is noun, adjective, adverb and preposition. In application, I agree with Mr. shiosai123 PAST - "过去" （名词） PASSED - "过了“ （PASS的过去形，动词） Mr. Richard, PASSED - "过了“ （PASS的过去形，动词）is the passed to be used as the past tense of the verb pass. Sorry, the explaination was written in Chinese.

I respectfully disagree with Mr. Wozitoya; it is more common for "passed" to be used as the past tense of the verb "pass" than as an adjective. For many examples, see http://dictionary.reference.com/browse/passed; look under the transitive and intransitive verbs "pass."

很好的问题! 我们美国人经常把这两个词写错！ 区别应该是这样: PAST - "过去" （名词） PASSED - "过了“ （PASS的过去形，动词）

Past: [previous time] In the past, people used candles instead of electric lights. [by] She walked past the grocery store on her way to school. Passed (past tense of "pass"): [went by] She passed the grocery store on her way to school. [met minimum requirements] He passed the history test. [transferred] He passed the ball to another player. [died (used with "on")] After a long life, he passed on. [excreted] He passed a kidney stone.