If you blow air across the end of a tube, you can excite resonant harmonics. This is a very simplistic view of the frequency spectrum based on different end conditions for sound harmonics in a tube. (The length of the tube is assumed to be after any "end corrections" have been made.) See the equations here.
A) If you increase the LENGTH of the tube, what happens to the frequencies in the spectrum (do they shrink or grow) - and why? (Hint: Think of the wavelength fitting in the tube.)
B) If you increase the VELOCITY of the sound, what happens to the frequencies (do they shrink or grow) - and why? (Hint: If wavelength fixed, how would velocity change affect the frequency?)
C) How does opening one end affect the spectrum (compared to the both-open or both-closed)? How is the difference between frequencies related to the fundamental and why? How are they related for the both-open or both-closed?
D) Suppose you knew the velocity, what kinds of ends, and two adjacent frequencies ... can you figure out the length? (Hint: set up equations to represent each frequency with n1 and n2 as unknowns. What is the relationship between n1 and n2?)