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Whirly Tubes

The Whirly Tube, also known as the lasso d'amore, corruga tube, corrugaphone, sound tube, musical tube, or Bloogle Resonator, is a musical instrument that consists of a corrugated plastic tube that one "plays" by swinging in a circle. In this activity, the students whirl their tubes at different speeds to produce various pitches.

The sound is created by air moving through the tube.

But why does air move through the tube? The answer is found in Bernoulli's principle. Bernoulli's principle states that as the speed of air increases, its pressure decreases. The free end of the tube moves through the air much more rapidly than the end that you are holding. Therefore, the free end experiences low pressure. The relatively high-pressure air in the tube rushes up to fill in the low-pressure area, creating air flow from the end you are holding to the free whirling end.

The sound is produced when travelling air molecules hit the tube's inner ridges and vibrate against them. As you whirl the tube faster and faster, the whirling end's air pressure is lowered, and air moves faster through the tube to fill this low-pressure area. The faster air means faster vibrations of the air molecules as they hit the inner ridges, and the pitch then increases.

A vacuum cleaner hose or garden hose will not produce a sound since there are no ridges on the inside to make air molecules tumble and bump into each other and thus vibrate. Air will rush through the hose but does not make sound!

Objectives

  • Describe the properties of sound.
    Describe what pitch is and how it varies.

Materials

Key Questions

  • What causes the sound as you whirl the tube? Can you increase the pitch? Why is no sound produced when you block the end of the Whirly Tube? Can you produce a sound by whirling any type of tube or hose?

What To Do

  1. Spin a Whirly Tube above your head or in a circle in front of you. 
  2. The tube should produce a sound. Change the pitch by experimenting with the speed of your whirling. 
  3. Put your free hand over the hand-held end of the tube while you whirl it. No sound should be produced. 
  4. Ask a volunteer to whirl the garden hose above their head.

Extensions

  • To visualize the air flow through the tube:
    1. Attach a plastic bag to the hand-held end of the Whirly Tube with tape or a rubber band.
    2. With your mouth a few millimetres from the tube, blow into the open (whirling) end. The bag will inflate with just a few big breaths.
    3. Once the bag is inflated, whirl your tube. As the sound escapes the tube, watch the bag deflate!
    • (see our Windbag demonstration under Other Resources for more information)

    Hold a handful of confetti near the bottom of the tube. The confetti is pushed up the tube and creates a real mess! Check out masters of the whirly tube; Walk off the Earth

Other Resources

Science World Resources | Full Unit | Sound

Science World Resources | Balloons | Activities | Windbag Demonstration