Crack is a term for crack cocaine. An abused stimulant drug. The drug causes you to be wild and stimulated. So the term, " being on Crack" is a slang term, meaning , yes the person is acting crazy, wildly out of control as if under the influence of crack cocaine. Getting crack would be a verb form of obtaining the drug itself. Now... I see you found an interesting English word that uses another phrase, " Get Cracking !! " is a completely !!!! different use of the word crack. Wow, how did you find this stuff ?? Haha.. Get cracking is just a slang phrase that means , indeed what you said, " get moving quickly " I can not tell you the etiology of that phrase, but its old English slang term, not related to the drug crack !! Confused ?? I am now...

On crack is slang for on drugs. So usually it implies that kind of questions, like is she insane/crazy? No, you can't say she gets crack. She gets crack means she gets drugs. That usually means she obtains drugs. You should just say, yes I think she may be on crack or I think she's on crack to say that she is possibly crazy because of the drugs.

Use the word "crack" very carefully because it has several meanings, some of which are fairly nasty. Leaving aside the term "on crack" which directly implies that the person being referred is under the influence of crack cocaine, there are several ways to describe a person who is behaving in an angry or frustrated manner. 1) Going nuts 2) Going crazy 3) crazy, mad, nuts, bonkers, and bananas all mean "insane" but can also be used in a derogatory way to describe someone who is behaving in a seemingly irrational way, perhaps from rage or frustration. 4) " He's cracked" or "He's a crackpot" has a similar implication to (3) above. 5) "get crack" does not mean anything like "going crazy". Please forget about ever using "get crack".