Tuesday, October 7, 2014

The sound and straw

By cutting the two lips of a soda straw, flattening the end, and blowing with just the right pressure, we can make sounds vibrate in the straw.
Flatten one end of the straw by sticking the end in the mouth, biting down with teeth, and pulling it out. Do this for several times to make flexible, flat-ended straw. Cut equal pieces from each side of the flat-ended so that straw has two lips at the end. Put the straw in your mouth and blow into the straw. You will probably have to experiment with blowing harder and softer while biting down with different amounts of pressure until you make the straw sing.
The monks here at CGI make straw reeds in same way to use it with Gyaling. Gyaling literally means "Indian trumpet" and is used during the monastery puja (chanting and prayer) and is associated with peaceful deities. All the monks know how to make and use this simple straw reed. Normally when they make them the reeds are shorter in length and can produce high pitch sounds. The reed goes on top of the Gyaling to make it sing.
So, the question we asked our class was ‘’What makes the straw reed produce sound?’’ To this question, the 20 students have responded with a few one-word guesses- air, pressure, vibration, high, low, hole etc. They were some pretty exciting responses. In fact, all the words that can explain the working of the straw reeds were spoken by them.
With supporting responses from the students, it was quite convenient for me to discuss the working of the reeds- when we blow through the straw, there is high pressure in your mouth. As air rushes through the straw, the pressure in the straw drops, and the high pressure outside the straw pushes the sides of the reed inward, closing off the flow. The pressure then builds inside the straw and pops the reed open again. This causes the vibration of the straw lips. When the reed vibrates at just the right frequency, there we hear loud, buzzing notes.

This is not only a good lesson on acoustic physics but also a fun way to reuse a straw.

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