BoomWhackers are excellent instruments for conceptualizing the connection between the wavelength of a pressure disturbance in air and the corresponding pitch. That is, they concretely "prove"/demonstrate the physics of sound waves. Students will need to know the parts of a wave and understand that there is an inverse relationship between wavelength and pitch (which implies an understanding that the speed of sound is a constant). Incidentally, we taught these preliminary concepts using large slinkies. Slinkies are great for this because the students can see directly that if you shake the slinky faster (pitch), the wavelength decreases. A few rough calculations can persuade them that the speed is indeed constant for all wavelengths. And finally, it is ideal for demonstrating longitudinal (sound) versus transverse (electromagnetic) waves.

  BoomWhackers are simply hollow plastic tubes cut to precise lengths in order to produce notes, e.g. A, D flat, etc. With the end cap on, you produce, say, middle C. Slide off the end cap and, voila, you get high C. I highly suggest reviewing the physics of waves with the students first, explain the BoomWhacker, and then make a prediction of whether the note will be higher or lower with the cap off before anyone ever hits a tube. It's a nice way to practice thinking about a problem, forming a hypothesis, and testing it in 20 minutes flat (more or less depending on the class).

  The physics is simple. Define the tube length as "L". With the end cap on, there is a node at the cap and antinode at the opening. Therefore one complete wavelength is 4L. Take the cap off and now there is an antinode at both ends and a node in the middle so the compete wavelength is 2L. That is, take the cap off and the wavelength (of the first mode - I didn't discuss this aspect except with a few students one on one) goes down by 2 so the frequency goes up by 2, i.e. the pitch goes up one octave. Ask if you have any musicians with perfect pitch hearing in the class and see if they can guess the note (printed on the tube). Take off the cap and see if they name the same note but up one octave. (It helps convince the students if another student verifies what you're saying.)

  BoomWhackers can be found at a number of online stores for less than $50. **Make sure you purchase (they come separately) the "Extra Octavator End Caps" that lower the pitch/note one octave.**

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