How to play Bottle Flute
- Choose a test and read the bottle's depth, the water, or the note wanted on the card.
- Use f = v ÷ 4L with v = 340 m/s and L the air column in metres; higher notes are 3f, 5f…
- Type your prediction and press Start. Watch the air swing and the water pour in.
- Compare the orange water line with the real one, and with the note on the graph.
Closed pipes
Blowing across the mouth of a bottle makes the air column inside vibrate at its own natural frequency, just like a string or an organ pipe. At the closed end, the bottom or the water surface, the air cannot move: that is a node. At the open neck it moves the most: an antinode. The longest wave that fits has a node at one end and an antinode at the other, so the column holds a quarter of a wavelength: λ = 4L and f = v ÷ 4L. A shorter column makes a higher note, which is why the pitch rises as you pour water into a bottle, and why a bottle filling under a tap sounds higher and higher. Blow harder and the column can hold three quarters of a wave, then five quarters: a pipe closed at one end makes only odd multiples, f, 3f, 5f, unlike an open pipe or a string, which make every multiple. Clarinets, pan pipes, and stopped organ pipes are closed pipes.
A focused learning model
The bottle is treated as a straight tube closed at the bottom or at the water surface, with sound at 340 m/s. Real bottles have a narrow neck and behave partly like a Helmholtz resonator, and the open end acts as if it were a little longer, so real notes are lower than f = v ÷ 4L. The air's swing is drawn slowed down to one swing a second. Answers within 2% are right.