1. The problem statement, all variables and given/known data We have high cilinder with height h a filled with water up to the height L<h and air in the rest. We hit the cylinder and listen to the frequency of its sound. How can we determine L in function of h, the frequency of the noise, the speed of sound, ... 2. Relevant equations 3. The attempt at a solution Maybe the sound has something to do with the harmonics on a string. Is the frequency =velocity of sound/(2*(h-L))?