2003 Virginia SOLs
Motivation for Learning
Questions to ask students:
An air column will vibrate with a wavelength dependent on the length of the tube, and, therefore, a certain pitch. The wavelength cannot be seen of course, but it can be seen that the longer the air column, the lower the pitch. When you blow across a bottle with water in it, the vibrating medium is the column of air whose length ends at the top of the water. Therefore, the more water that is in the bottle, the shorter the column of air, and the higher the pitch. When the same bottle is struck with a mallet, the vibrating medium is the glass and the water. The more water that is in the bottle, the more vibrating material there is (longer column), and the lower the pitch when struck with a mallet.
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When you blow on the end of the straw, the two pieces of the tip vibrate together. This makes a vibration, which is necessary to make sound. The tips vibrate at a specific frequency and wavelength that is determined by the length of the straw. The vibration travels down the straw and reflects from the end. This sets up a wave in the air in the straw; the vibration will bounce back and forth between the two ends. It is this vibration that you are hearing. Changing the length of the straw (by clipping it off, or by making a straw trombone) changes the wavelength and frequency, and so changes the pitch. Making a hole in the straw so it is like a real instrument lets the vibration bounce off from where the hole is, which will also change the pitch. Similarly, hitting the pipe causes it to vibrate, and the frequency and wavelength depend on the length.
Have the students compare straws and pipes of different widths. Have them try different designs for the straw's tip. Which one works best? Does it make a difference how hard you blow into the straw? Tune the instruments to simple notes, and have the students perform an easy song, such as "Mary Had a Little Lamb." You could also explain how vocal chords use the same principle to make different pitches.
Students with Special Needs
Many students may not be able to get a noise out of the straw oboes. These students can cut the straws while the other students are blowing through them. They can also adjust the "trombone slide" as another student is playing the oboe.
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