sorry for the "bad" title, I couldn't think of anything else. We all have seen the experiment where you take a hair dryer and a ping-pong ball and the hair dryer blows the ball into the air and you can move and tilt the ball around... now, that is a very simplified version of my final years engineering project. the question I have, and what I cant seem to explain is about the forces acting in on the ball to keep it in the air. Bernoulli's law keeps the ball from falling out of the air stream (in this case created by a centrifugal fan), and the drag force on the ball is what keeps it in the air vertically. I calculated the velocity of the air needed to produce the required drag force, but is there a way to calculate the theoretical height at which the ball will levitate in the air? I know the exit velocity of the air from the nozzle, (for my experiment, just a straight PVC pipe with a 110mm diameter), and the calculated velocity for the drag force is 5.7m/s.