"Break open" - what is "open"? An adverb, noun, adjective or verb?

Question

In the phrases "break open" and "break [sth.] open", is "open" an adjective or an adverb? Is it an adverbial or a complement?

For example:

The pods broke open and the seeds scattered on the wind.

The police broke open the door.

The burglars broke the locked safe open.

Answer 1

[EDIT - post comments] Before reading my answer, please review the links John Lawler provided in the comments above. It's here for convenience: https://english.stackexchange.com/search?q=user%3A15299+phrasal+verb I am not so convinced my answer is sufficient based on his and user:deadrat 's comments below and those above, but I'm leaving my answer here as an example of what seems to be a common misunderstanding, an over simplification, of a more complex subject.

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All those forms are based on "broke open," making open an adverb. How was it broken? It was broken open.

Similar constructions, e.g.:

The police bashed in the window.
The police broke up the protests.

( Not sure, if this is considered a compound form ?)

But if you had, say:

The guard closed the open door.

then open would be an adjective. What kind of door? An open door.

Answer 2

The word open has a lot of definitions as different parts of speech. Its primary entry for Webster's is that of an adjective; however, scrolling down under this definition, you'll see also that it can function as an adverb.

Thus, break open would be diagrammed as:

break | open

verb | adverb

It is not a complement (break is an action verb here, not a linking verb, and adverbs are not used as objects). It is adverbial. http://www.merriam-webster.com/dictionary/adverbial

http://www.merriam-webster.com/dictionary/open

Also, http://dictionary.cambridge.org/us/dictionary/english/open

The definition of open as a noun doesn't seem to fit "break open"; again, omitting it as an object

Since adverbs modify adjectives, verbs, and other adverbs, this one is modifying break and like an adverb, it answers a question about the verb that an adverb would ask, " What?" "Break what?" Open.

For example,

This is the police! Open the door, or we'll break open the door! [They'll break the door, but not how, but what are the police going to do with or to the door (they will use extreme force to open the door) and (of course here, "door" is the direct object)]

"Break down" the word down is the more common expression they would use, but here too, down is an adverb, the noun definition doesn't seem to fit.

http://www.merriam-webster.com/dictionary/down