Whirly - The Twirling Sound Hose At first glance, it looks like your ordinary plastic tube. email to friend
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Spin the tube faster and notice how the pitch of the note goes up. Fast twirling creates high pitch notes and slower twirling creates lower notes. Amazing!

The Bag "Whirly"

1. Attach a plastic bag, such as a garbage bag or shopping bag to the end of your Sound Hose with tape or a rubber band.
2. With your mouth a few millimeters from the Sound Hose, blow into the open end.  The bag will inflate with just a few big breaths.
3. Once the bag is inflated, twirl your Sound Hose.  As the "music" plays from the hose, watch the bag deflate!

How does it work?

Imagine that the tube is filled with tiny pebbles. Twirling the tube overhead would shoot the rocks out of the tube. The same thing happens with the molecules of air. As you twirl the tube, air molecules are launched out of the other end. The faster the twirl, the faster the molecules come flying out the other end.

The Bag "Whirly" experiment creates a stunning effect because of the air molecules quickly exiting the Sound Hose.  The plastic bag helps your audience visualize the movement of the molecules because you can see the bag deflating as the Sound Hose is being "played."

Not all plastic tubes sing. The tube must be corrugated on the inside. Why? The aerodynamics researchers in Japan put a whirly in a wind tunnel and used very tiny hot wire anemometers to measure the airflow near the corrugations. As the air flows first over one ridge then over a second it tumbles into a vortex. The faster the air flows through the tube the higher the frequency of the sound produced by the vortex. When the frequency of the vortex matches one of the natural resonant frequencies of the tube it is amplified.

Notice how the inside of your vacuum cleaner hose in NOT corrugated! Otherwise, your vacuum cleaner would play music (maybe a poor choice of words) whenever you cleaned the house.

In Search of More Tubes... While the toy store “Twirly” is fun, you’ll soon want to experiment with different size tubes (long, short, fat, skinny) to see how the size and shape change the sound.

Additional Info

Information for this article was gathered from a great website presented by Paul Doherty from the Exploratorium. For much greater detail on the Singing Tube, visit Paul's website.