Why does blowing over bottle make a note ?
Resonance in acoustics occurs when some mass-spring combination is supplied with energy. Many musical instruments rely on air resonance to improve their sonority. If you blow across the mouth of a bottle you can often get a note. The bottle behaves as Helmholtz resonator. The main volume of air inside the bottle is analogous to a spring, whilst the “plug” of air in the neck acts as an attached mass.
