Controlling Speed

I have a movie clip I'm duplicating twice to drop from the top to the bottom of the stage- currently all 3 copies drop at the same rate, I'd like to get them to drop at different speeds, and I'm finding it to be a little challenging.... Thanks for any help.....

on each clip:

onClipEvent(load){
top=0; //or wherever you want the clip to start
bottom=400; //or whatever the height of your movie
speed=10; //vary to change speed of drop
_y=top;
}

onClipEvent(enterFrame){
if(!stopped){
_y+=speed;
if(_y>bottom){
_y=bottom;
stopped=true;
}
}
}

should do it.

Thanks! I'll give it a try