Created by Dale Olive and Randy Scoville
Future Flight Hawai`i instructors
Demonstration at a glance:
A three foot long piece of corrugated plastic tubing is swung overhead at various speeds producing different pitches of sound.
Obtain a "Whoop tube" from a scientific catalog or toy store (I also tell students to just pull off the vacuum cleaner hose if they can't find one.) Twirl overhead at varying speeds to produce different pitches of sound.
The sound comes from the fact that the ribs in the hose are vibrating air. One question you could ask "is the air being vibrated by the ribs on the outside or inside of the hose?" The fact that a pile of cut paper is picked up by the hose tells you the sound is coming from the air being sucked up into the tube (see Bernoulli Head Lice Detector Demo.) Why is it sucked up? It's explained by the Bernoulli principle. Bernoulli stated that the faster a fluid (air is a fluid) moves the lower the pressure it creates. In this demonstration, the end of the twirling tube is moving faster than the end in your hand creating lower pressure on the fast moving end. The higher pressure on the still end forces air up into the tube. Hold your hand over the tube and notice how the sound disappears.
Besides the "Head Lice Detector" mentioned above, I sometimes use this demo to show the "Eternal Whistle." Standing by a door with the tube twirling outside, an audience inside thinks you are whistling eternally. Of course, you can only last as long as your arm can twirl. I try to show a look of pain on my face as the whistle is prolonged (this is often due to the pain my arm feels after a few minutes of twirling.)
Communications: Hawaii Space Grant Office
This activity is featured in Future Flight Hawaii, a K-12 Education Project of Hawaii Space Grant Consortium.
FEB 27 2001.