Hi.....can anyone help out explain the relationship of diameter to velocity of air flow thru a tube for the following science experiment. A photo is attached. The question they are trying to answer thru the attached experiment is: Does the diameter of the tube affect how high a ping pong ball will be raised? Three rigid clear plastic tubes attached to a board. A small balloon (with both ends cut off) is stretched over the bottom end and a ping pong ball is put into it and it rests on the bottom. To the other end of the balloon (the narrower neck of the balloon) a flexible tube/hose is attached and thru which air is pumped into with an inexpensive balloon pump (see photo - only one tube is shown for set up, but they are testing each of diameters 1/2", 5/8" and 7/8" of flexible tubing). The pump of air causes the ping pong ball to rise a certain level and they record this. Assuming that the same person uses the balloon pump for each of the three trials, they are assuming the "pressure" to be the same. The question is .....is there a simple relationship between diameter and velocity if air flow thru the tube which can explain why the larger diameter raises the ball higher. Initially, my son thought intuitively that the pressure would be greater in a narrower tube - which I believe is correct - but is there a relationship between pressure, diameter and velocity that can easily explain this. any help would be appreciated.