These two words are commonly mistaken for each other or thought to be able to be used interchangably.
PAST refers to a previous time:
• History refers to past events.
• I knew Robert in years past, but would not have recognized him today.
• Past behavior is often predictive of future behavior.
PASSED is the past tense of the verb TO PASS and has several meanings:
• It can mean to have skipped your turn: Erica passed her turn at bridge.
• Another meaning, in sports, is to have moved an object from one player to another: The hockey player passed the puck to his teammate.
• It also represents the movement of going by another person: Jessica passed (by) her ex-boyfriend in the hall but pretended not to see him.