Physics of Music Physics 121

Assignment 5

1. Hall, Chapter 4, page 69, Exercise 1.
2. Hall, Chapter 4, page 70, Exercise 6.
3. Hall, Chapter 4, page 70, Exercise 8.
4. Hall, Chapter 4, page 71, Exercise 15.
5. Go to your favorite telephone with a reasonably long cord. Stretch out the cord a bit by moving the receiver away from the phone. Now move the receiver in your hand back and forth to make transverse waves propagate down the line. Change the rate of your back-and-forth motions until you produce a standing wave. Experiment until you produce standing waves with one, two, three (and possibly 4) antinodes. Now that you have a feeling for this, you can be more quantitative. What happens to the frequency of a particular mode if you stretch the phone cord? Pick a fixed length of the cord and measure the frequencies for the one, two, and three antinode resonances. How are these frequencies related to each other? Is this what you expect? Hint: as with the pendulum, it's easiest to measure the time required to complete 10 periods. Once you know the period you know the frequency. Estimate your errors. Have fun.
6. Secure a nice Coke bottle and learn to play it by blowing across the top. Careful...Don't hyperventilate! As you drink away the coke in the bottle, what happens to the pitch? Start with about a centimeter of water (Coke, etc.) in the bottom. Can you identify this pitch using another instrument? Mark the side of the bottle at the water level. Now add water until the pitch goes up by one octave. Mark this spot. Measure the distance from the two water marks to the top of the bottle. Can you explain the relationship of these two distances? Is the pitch of the bottle what you would expect from simple ideas of open and closed tubes.