A tuning fork is set into vibration above a vertica oepn tube filled with water. The water level is allowed to drop slowly. As it does, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning work? The answer given on the back of the book is 635 hz. Not only do I have no idea how the book got this answer, but this answer is also is less than the fundamental frequency of a 0.125 m closed tube, which is 686 hz. Could someone provide an explanation?