From Vibration To Sound

Persons, Pamela Walt Disney Magnet School

Objectives: 1. To identify the parts of a sound wave. 2. To distinguish between a transverse wave and a compressional wave. 3. To describe how musical instruments produce sounds. Apparatus Needed: An overhead projector, plastic dish, glass, corks or stoppers of different sizes, tuning forks, rope, slinky, tin cans, string, paper clips, test tubes, test tube rack, student-made instruments, rubber tubing, 6 V cell and connecting wire, a jar of vacuum grease, electric vacuum pump and stand, bell jar and electric bell. Recommended Strategy: 1. Discuss that sounds we hear are vibrations of molecules in air and other materials. They carry energy in waves that can be reflected, absorbed and transmitted like light waves, but cannot travel like light in a vacuum. 2. Place a large square, clear glass or plastic dish on an overhead projector. Fill the dish one third full of water. Drop corks or stoppers of different sizes into the center of the water and project the resulting wave motion onto a screen. Discuss what caused the waves and their characteristics. Now strike a tuning fork and touch the stem to the surface of the water. Observe the wave pattern produced. Discuss the cause of waves. 3. Tie one end of a rope to a doorknob. Produce transverse waves along the rope by shaking one end. 4. Use a long slinky-type spring to illustrate longitudinal and transverse waves. 5. Point out that wavelength can be measured from crest to crest, trough to trough, or any other two corresponding points. 6. Diagram a wave and label its wavelength and amplitude. 7. Relate sound to mechanical vibrations of all sorts. For example, a drum beat, the snap of a breaking stick, a truck rumbling by on a street. Discuss the vibration one can feel in the speaker of a stereo. 8. Explain the scientific meaning of "tuning in" a certain radio station (the adjusting of the circuit in a radio so that the circuit resonates electrically at the broadcasting frequency of the radio station). 9. Use student-made instruments to illustrate volume and pitch (one- string guitar, earharp, sandpaper blocks, paper tube kazoo, wind chimes, wood block tambourine, tongue depressor finger piano, garden hose recorder, etc.) 10. (IF AVAILABLE) Set up the demonstration of a bell in a vacuum. With the bell ringing, pump the air out of the bell jar, and then allow the air to fill the system again. Discuss why the sound of the bell gets fainter until no sound can be heard. 11. Prepare "learning stations" with independent activities related to the production of sound. For example: A> Waves in a Coil Spring (To demonstrate a compressional wave) B> Talking Through A String Telephone (To hear the transmission of sound) C> Tuning Fork Sounds (To discover how pitch is related to the frequency of sound waves) D> Test Tube Organ (To determine how the length of an air column affects the frequency of the sound) 12. As enrichment activities students could research the following: 1). Seismic waves transmit the energy of an earthquake. Research earthquakes to determine the types of waves made. 2). Traditionally, soldiers break step when crossing a bridge. In the 1800s a group of soldiers crossing a bridge in step set up a vibrational pattern that caused the collapse of the bridge. Research this incidental bit of history under the topic of bridges or vibrations.
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