This video shows how a flute can be used to come to some conclusions about the relationship between the length of the air column and the pitch produced. The note produced with all the holes closed is the lowest and that with all holes open is the highest, with a step wise variation in the middle. This shows that longer columns produce lower notes. Try this with similar bottles filled to different heights with water, and blow over the mouth of the bottle to produce a note. Can you predict beforehand which note will be the highest, and which the lowest?