Squawker

Purpose: Students will explore resonance and how the pitch of a sound can vary with the length of an object.

Materials (per student)

• 3 straws
• scissors

Procedure

1. Have the students flatten the last inch of one end of their straws. This is easily done with a ruler.
2. Then ask them to make two diagonal cuts to the flattened end of the straws. (See Diagram 1 below.)

3. Tell students to blow through the straw to create a "squawking" sound.
4. Ask the students what part of the straw is vibrating to make sound and what part of the straw acts as a resonator.
5. Ask students what they think will happen if the straw is made shorter.
6. Have them predict how the pitch will change.
7. Test the class prediction. Have a student blow through a straw while another student cuts the straw to a shorter length. To hear the change in pitch, make the cut while the student is still blowing. For younger students, take the straw out of the mouth, cut, and then blow again. The class may use the sounds produced by these new straws to figure out how pitch changes with length.

What's Happening?
The squawkers make sound by producing vibration. Moving air causes the vibration. Moving air causes the pointed ends of the straw to move rapidly back and forth. Woodwind instruments, such as clarinets, use a reed that vibrates in a manner similar to the pointed end of the straw squawker.

The length of the straw, in part, determines the kazoo-like sound that is created by the straw squawker. As the length of the straw becomes shorter, the pitch of the sound will become higher because the air in the shorter straw naturally resonates at a higher frequency. Sound waves with a higher frequency result in a sound with a higher pitch.

Conclusion

1. Review the definition of sound, resonance, pitch, and vibration. How are sound, resonance, pitch, and vibration related?
2. Why did the pitch become higher as you clipped the straw shorter and shorter?
3. How did the squawker make sound?