Centrifical Force!

[Connor S.]

Which is the correct spelling of the word?

Obviously its Centrifical.

[Mr.Onion]

There is no entry for "centrifical" in dictionary.com.
There is no entry for "centrifical" in Wiktionary.org.
AFAIK, there's entry in the OED either. :p

[Coolguy]

It's centriFUGAL! :p

And doesn't centripedal mean something else?

[CheeseLord]

They are different forces, but the question wasn't asking about that.

[AtkinsSJ]

Centrifugal force doesn't actually exist, and centripetal force makes no sense in my head, really.

So both of the two bottom options are correct.