Idea 4of 6Builds onOnly the fits survive
One end open
Blow across a bottle. What fits inside it?
Today you'll discover
- what an open end is, in a standing wave
- the smallest piece of a wave that fits a closed column
- how a bottle's note depends on its depth
Think firstA column of air, closed below and open above
Air in a bottle hums. At the closed bottom and at the open top, how does the air move?
Predict first, then drag the length. Watch the fitted wavelength and the note.
An air column drawn as a tube closed at the left and open at the right, with a quarter of a wave inside: a still point at the wall and the widest swing at the opening. After a prediction, the length is bracketed as a quarter wavelength, then the column-tuner bench opens with a length slider and readouts for the fitted wavelength and the note. The last step asks what happens as a bottle fills.
See the whole ideathe big idea and the key word, in one place
The big idea
A closed air column fits a quarter wavelength, λ ÷ 4.
Compare themString fixed at both ends: halves fit, L = n λ ÷ 2. Column closed at one end: quarters fit, L = λ ÷ 4. The rule behind both is where the nodes must be.
Key word
- air column
- the air inside a tube or bottle, which hums at the wavelengths that fit between its ends
About this modelOnly wavelengths that fit the length survive; the rest cancel within a few reflections.
Only wavelengths that fit the length survive; the rest cancel within a few reflections.
Ready to use it?
- Find the fundamental of a closed air column of given length, with v = 340 m/s.