Physics experiment with sound I am doing an experiment for a school project which consists of blowing into 6 different bottles to create different notes/harmonics. Each bottle is filled with different volumes of water to create a different sound. I have to calculate the theoretical frequency of each, but I do not know how.
 A: This is called a Helmholtz resonator, a kind of mass-spring oscillator where the mass is the mass of the air in the neck of the bottle, and the spring comes from compression of air in the main volume of the bottle. A formula for the resonant frequency is given here: https://en.m.wikipedia.org/wiki/Helmholtz_resonance
A: I want to add to the answer given about Helmholtz resonator.
What you are expected to calculate (in principle) is the resonance of sound waves in a tube which has one side closed (your bottle). In this simple case the frequency of the different nodes depends on (among others) the length of the tube. As you fill water to your bottle, you decrease the length of the tube, that is, the empty region (air) in your bottle where sound waves interfere. This will cause the resonance frequency, therefore, the pitch of the sound to change.
I suggest you to look at
https://openstax.org/books/university-physics-volume-1/pages/17-4-normal-modes-of-a-standing-sound-wave
and scroll down to section called Resonance in a Tube Closed at one End.
