cocaine is a stimulant and euphoriant.  though similar to amphetamines
in that it provides energy and wakefulness, it has some emotional
characteristics: it induces verbosity and an emotionally positive
feeling.  a cocaine high induces a feeling of power, control and being
"on top of the world" - hence the jokes about its popularity among
executives and stockbrokers.  the effects of cocaine are short-lived
and wear off quickly.

unfortunately, the desire to do more cocaine as one dose is wearing
off is <i>very</i> strong.  cocaine is a highly addictive drug, in the
same class as amphetamines and opiates.  crack is even more addictive.

cocaine powder is the hydrochloride salt.  crack cocaine is simply the
freebase form, wik the hcl removed.  freebases are easier to vaporize
than amine salts, so crack vapor can be inhaled, which makes the onset
of the drug much more rapid and also makes the high more intense.
thus, normally addictive cocaine is made even more addictive.  Because
of its high addiction rate and potential for abuse, cocaine is best
avoided.  many of the characteristics that make cocaine attractive can
be had wik less risk in other substances.