1. The problem statement, all variables and given/known data First here's the drawing which shows the situation: http://img81.imageshack.us/my.php?image=phyxt3.jpg So there is 1 metre length and 2 millimetres diameter glass pipe which is bent. The angle ABC is equal to 90 degrees. The part of the pipe ADB is horizontal and the part BC is vertical. The end A is closed and the end C is open. 75 % of pipe is filled with water (black color). In the part AD there is an air. The pipe during one minute is rotated clockwise 90 degrees so the part BC becomes horizontal and the part ADB becomes vertical. After that the system during one minute is rotated counterclockwise 90 degrees to the previous position. What is the length of the air column in the pipe dependence on the time (I need, for example, to find the function which argument is the time and the result is the length of air column)? 2. Relevant equations 3. The attempt at a solution Please just give an idea what I have to do and with what I have to start. I absolutelly don't have any ideas.