Passed is only used as a form of the verb "pass," whereas past functions as a noun (the past), adjective (past times), preposition (just past), and adverb (running past).

Do I use past or passed?

Both past and passed can be used of motion and time. The word past can be used as an adjective, a preposition, a noun, or an adverb. The word passed is the past tense of the verb pass. ... When past is used as an adjective it refers to a time gone by or something from, done, or used in an earlier time.

How do you use the word passed?

The word passed is the past tense of the verb to pass. The verb pass, when used in present tense would look like this: I will pass the ball to you. If you substituted the word pass for passed, I passed the ball to you, it signifies that this happened previously. That is has already happened.