Whirly – The Twirling Sound Hose
At first glance, it looks like your ordinary plastic tube.
You wouldn't think twirling a hose over your head could make music, but you'd be surprised what you can discover at the hardware store! You might get a few strange stares, but who cares – it's all in the name of science.
- The "Singing Tube" is a popular and inexpensive item in toy stores. There is really nothing to it - a corrugated plastic tube measuring about 3 feet long and 2 inches in diameter.
- If you can't find the official "Singing Tube" just use a piece of irrigation tubing from the hardware store.
- Plastic bag (garbage bag or shopping bag)
- Rubber band
- Hold one end of the tube and twirl the other end in a circle over your head.
- 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!
- Attach the plastic bag to the end of your Sound Hose with tape or a rubber band.
- 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.
- Once the bag is inflated, twirl your Sound Hose. As the “music” plays from the hose, watch the bag deflate!
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.
Take it even further and try something altogether unique. Buy a piece of large diameter corrugated tubing from the hardware store and on the way home (while someone else is driving) put one end of the tubing out the window and see what kind of sounds you can make as the speed of the car increases. As other drivers send you nasty looks, just scream out the window, “It's science, people!” Try it on your next road trip. (Check out the video tab if you're curious.)
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 bag part of the experiment creates a stunning effect. The plastic bag allows you to see the movement of the molecules when you watch the bag deflate as the Sound Hose is “played.”
Not all plastic tubes sing. The tube must be corrugated on the inside. Why? 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 is NOT corrugated! Otherwise, your vacuum cleaner would play music (maybe a poor choice of words) whenever you cleaned the house. That would be one way to get out of doing your chores!
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.