Dimples work on a golf ball because the shape of the ball is not aerodynamicaly efficient. The dimples cause the air to break free of the back side of the ball. this is good because the ball (if it were smooth) is asking the air to follow the surface of the ball all the way around to the back. This pulls back on the ball more than if the air were to break free. A tear drop is an aerodynamically efficient shape. Think of what the air looks like if it were to break free of the back side of a ball. The air breaks free of the ball and gradually closes in to itself some distance behind the ball. This patern looks just like a teardrop.