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Name: Julia E. R.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: Saturday, April 20, 2002 8:17:44 PM


Question:
We are doing a community TV show on Sound. It is a live, call-in show geared toward 4th and 5th graders, but with respondents K-8th grades. We are covering vibration (sound is results when matter is vibrated), pitch, loudness, and waves (a wonderful physics teacher from ETHS is joining us with his wave machine.) I need some whiz bang, keep their attention, experiments with sound. Perhaps including instruments. Thanks!


Replies:
Julia,

One possible experiment might involve something such as a guitar. If the string is plucked, a pitch with a wavelength of twice the string length will result. It will not be a pure wave. It will have many harmonics, twice the pitch, three times it, four times and so on will exist. Placing a knife-edge firmly at the halfway point will not eliminate the sound. You will get a much quieter sound with a pitch exactly one octave higher: half the wavelength and twice the frequency. Placing the knife-edge 1/4 of the way from either end will result in a 2 octave increase: 1/4 of the wavelength and 4 times the frequency. Anyone who knows how to play a guitar can point out these locations on the neck of the instrument. He/she may even know the locations without understanding why they work as they do.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



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