Think of it in terms of beer of hard liquor. Coke is much like beer, crack leans more towards hard liquor. It is more intense but does not last as long. On the rare occassions that I decide to smoke crack, when I have the cash to spare I will get a rock for myself, sit in a confined area or out doors and smoke it all within half an hour.
Coke was more for combating boredom in class. Crack produces this temporary, indescribable rush as if everything is okay, as if you're fine but everything around you is fucked up, it feels so heavenly and I want some right now GOD DAMNIT I'D HOLD UP A GAS STATION I WOULD.