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Kroogah Tubes
# 3D30.35

Description: When spun above your head, turbulence is created by the moving air through the tube. This turbulence is compounded by the ridges in the sides of the tube. Sound waves traveling out of the open ends of the tube partially reflect back into the tube. If the wavelength of the reflected wave matches the wavelength of the incoming wave, these waves reinforce one another, resonating of greater amplitude.

Many different wavelengths are produced. The waves that resonate have a wavelength that is equal to the length of the tube, or the tube length must be evenly dividable by 1/2 wavelength. If you increase the speed of the spin, the frequency will increase and you will begin to hear overtones.

Kroogah tubes can be purchased from many scientific equipment vendors or purchased directy from any hardware store's plumbing department.

Purchased/Built: purchased

Setup Time: none

Quant. in Demo Room: 3

Demo References
Freier and Anderson Se-6 Open tubes of corrugated plastic are whirled around.
Freier and Anderson Se-7 A freq tube is attached to coffee can moved up and down in a pail of water.
The American Journal of Physics AJP 42(4),278 The complete explanation on singing corrugated pipes.

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