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.

Questions:

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?)