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Sound Off

In one week our school’s Math and Science Night will be upon us. This year I will be hosting a room and it’s going to be noisy – we will be exploring sound. Besides having a variety of noisemakers to play with, here is a preview of two not-so-melodious activities we will share.

Hanger Gong

Take a plain metal coat hanger and two pieces of string a foot or two long. Tie one end each string to the corners of the triangle that are furthest apart. Take the other ends and wrap it around each index finger a couple of times. Then stick your fingers in your ears. You should look a bit like this guy on the right. (Photo Credit)

Now just lean over so the hanger hangs free and let it bump against a table or other hard object. If you have a friend around, have them use a pen to tap the hanger. To the outside world it sounds like dull tapping but to the one wearing the gong, it is music in your ears!

How does it work?  When the hanger is bumped or tapped, it vibrates.  The vibrations travel through the air to your ear and are heard as sound.  However some objects, like string, transmit these vibrations better than others, like air.  More of the vibrations make it to your ears via the string than the air.

Straw Oboe

These are fun to make at a restaurant when you’ve been waiting for a very long time.  The wait staff will be highly motivated upon hearing the noise delightful music these instruments produce.

Take a standard plastic drinking straw and chew on one end until it is flat.  Use a pair of scissors (or nail clippers if you are in a pinch) and snip the top into a pointy triangle.  Squeeze the top of the straw so the two chewed up triangles separate.  What you now have  is a double reed oboe! (Photo Credit)

To create a sound, hold the end of the oboe loosely in your mouth and blow very hard.  As the two reeds (aka end of the straw in your mouth) vibrate, a sound not unlike a duck call is made.

You can change the pitch of the sound by changing the length of the straw.  Try shortening your straw but cutting off about an inch at a time and observe what happens to the pitch.  A shorter straw produces a sound with a shorter wavelength which results in a higher pitch.  How high can you go?  If you are fortunate enough to have another straw that is slightly larger in diameter you could even make a trombone!