The line
[pascal]
procedure TVerletSystem.Update
...
Item[i].Force := Item[i].Mass * Force;
...
[/pascal]
looks susopicious to me (units don't match ). Since the force acting on the item is multiplied by its mass, the acceleration ( calculated in the TVerletItem.Integrate procedure) is the same for all items. That is why mass does not affect the motion.
I think You should remove multiplication by mass.