2003 Virginia SOLs
Motivation for Learning
Demonstration of Sound Vibrations
Questions to ask students:
The pitch of a sound is determined by the frequency of vibration of the source, in other words, how many times it vibrates per second.
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Follow directions in Data Sheet and record observations.
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1. Press a plastic or wooden ruler down on the edge of a desk so that half of it hangs over the edge. Give the end a flick and observe the vibration and note the pitch. Vary the position of the ruler and where you hold it down. Note how this affects the frequency and pitch.
Was the sound higher when the ruler moved up and down more quickly, or more slowly?
Was the sound higher when the ruler end was longer or shorter?
Using the above two answers, how are pitch, frequency, and wavelength related?
2. Hold a bike wheel by the axle and give it a spin. Hold the ruler so the spokes strike it, making a flapping noise. The faster the wheel spins, the greater the frequency and the higher the pitch.
What happened to the pitch when the wheel was spun faster? Does this agree with your results from the ruler?
3. Use the rubber band to attach the marker to the ruler so that the marker tip extends beyond the end of the ruler by about one inch. Lay the ruler on a book so that it extends about halfway over the edge. Tape the ruler securely in place (rubber bands work also). Hold the paper in front of the marker so that the marker's tip touches the paper on the left side. Have a partner pull down on the ruler and let go. Move the paper from left to right, and try to get a waveform on your paper. It may take a couple of tries. Try to pass the paper by at the same speed each try.
Now move the ruler so that it extends way beyond the table, and repeat. Try to get at least two different, good waveforms.
Look at the graph paper. How do the wave forms compare for when the ruler stuck way out versus when there was a shorter portion hanging over the edge of the table?
Measure the number of squares between the tops of two humps on each of the curves. How do they compare?
Count the number of waves between two vertical lines five squares apart. How do the graphs compare? Does this agree with your earlier conclusion?
Answers to Worksheet
Students with Special Needs
All students should be able to participate in this activity. Students who are unable to manipulate the ruler or wheel may work with partners.
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Data sheet to be completed during the laboratory.