Download Chapter 13 Sound

Name
Class
Date
Sound
HW Sound Problems
HW Sound Wave Theory Review
Go to http://www.youtube.com/watch?v=j-zczJXSxnw or http://www.dailymotion.com/video/xfcaer_tacomanarrows-bridge-1940_shortfilms#from=embed to see the power of resonance. This involved a repeated movement in the
bridge as a result of moving wind, but resonance more often happens with objects being affected by sound. (5:57 ea)
Watch a resonance demo using two mounted tuning forks.
What is sound?
Sound propagates through a medium by hitting one molecule to the next to the next.
1. Is a sound wave longitudinal or transverse?
Go to http://www.youtube.com/watch?v=33SrgAn7hao. (14 sec)
2. What’s wrong with this scene? What’s wrong with the weapon feasibility?
3. Is sound an electromagnetic wave or a mechanical one?
Go to http://www.youtube.com/watch?v=REqxyVlT45M&feature=related. Answer 4-17. (3:20)
4. What is sound?
5. What is a medium?
6. What has to be present or occur for a sound to exist?
7. How do waves move through a medium?
8. What mode of heat transfer is this similar to?
9. High air pressure equals areas of compression/rarefaction?
10. Low air pressure equals areas of compression/rarefaction?
11. How is wavelength measured?
12. What is amplitude?
13. What is frequency?
14. What is the unit for frequency?
15. What does the frequency of a wave depend on?
16. What is pitch?
17. A sound with a high frequency is heard as a high/low pitch?
https://www.youtube.com/watch?v=Ude8pPjawKI for fun stuff. (3:00)
Just like visible light is the only part of a continuing range of electromagnetic waves humans can see, audible
sound is the only part of a continuing range of sound waves humans can hear.
Just like bees can see ultraviolet and snakes can see infrared, dogs can hear ultrasonic sounds and elephants can
hear infrasonic sounds.
Just like owls can see in low light intensities and we can’t, owls can hear much quieter sounds than we can, too.
This makes a graph of the sounds we can detect a two dimensional graph.
18. What does “audible” mean?
19. Is a sound with waves that pass by 25 times a second at an intensity of 1x10-8 audible?
20. What is the intensity and frequency range of speech?
21. What does “ultrasonic” mean?
22. Even though we can’t hear ultrasonic waves, we still use them. How?
23. Does sound moves faster when the medium is more dense/less dense?
24. Propose an explanation for your answer.
Go to http://www.youtube.com/watch?v=d-XbjFn3aqE. Watch the demo on the speed of sound in gasses. (3:38)
25. In this case, sound moves faster when the medium is more dense/less dense?
26. Propose an explanation for your answer.
The speed of a wave is responsible for the Doppler Effect. When talking about light, it’s called a Red Shift or a
Blue Shift. It’s used to determine if a distant star is moving towards us or away from us. When talking about
sound, it makes a distinctive change in pitch.
Go to http://www.youtube.com/watch?v=yWIMWqkcRDU for an explanation of the Doppler Effect in light and
sound. (2:20)
Go to http://www.youtube.com/watch?v=Y5KaeCZ_AaY and http://www.youtube.com/watch?v=Kg9F5pN5tlI,
for a more irreverent explanation. (1:15, 2:00)
27. How could a blind person use the Doppler Effect to tell where traffic was going?
https://www.youtube.com/watch?v=PLPEcu6523Q (4:41)
28. What is the visual effect of a light moving closer?
29. What is the visual effect of a light moving farther away?
30. What is the auditory effect of an object moving closer?
31. What is the auditory effect of an object moving farther away?
Go to http://www.youtube.com/watch?v=cK2-6cgqgYA. Answer #32 - 47 and complete the sentences. (10:17)
32. What are the three different sources of sound?
a. Vibrating
b. Vibrating
c. Vibrating
33. How does a tuning fork make sound?
a. When the prongs are struck, they begin to_______________.
b. Vibrations set up invisible waves in ________________________________________.
c. Struck prongs cause _________________________________ as they spring back and forth.
d. This motion sets up waves.
e. The speed of the waves depend on _______________________________________________.
f. When prongs move apart, they push against adjacent air.
g. Where air is pushed together, _________________________________________ are formed.
h. When prongs move together, they create a partial vacuum and air spreads out to fill the
space.
i. Where air is spread apart, _________________________ are formed.
j. The number of times an air molecule moves back a forth in one second is the
___________________ of the wave.
k. In one complete vibration, sound moves a distance of ______________________________
l. The speed of a wave is its ___________________ times _____________________________.
34. What kind of instrument records longitudinal sound waves as transverse markings?
35. What is the modern recording instrument called now?
36. Condensations (compressions) cause the stylus to move ______________.
37. Rarefactions cause the stylus to move _________________.
38. Why do these directions make sense? (consider the label for the y axis on a graph depicting a
longitudinal wave)
39. What are three auditory qualities of sound? Describe each one.
m. Loudness
i. The larger the displacement of the molecules, the greater the wave’s ____________.
ii. The greater the amplitude, the greater the _________________.
n. Pitch (pay attention to the lower of the different pitches) (listen to the C, G, C demo forks)
i. Greater frequency equals higher/lower pitch?
o. Quality (timbre) more later about this.
40. The parts of a string with no motion in a standing wave are called ___________.
41. When a string vibrates along its full length, it’s at its longest possible wavelength. It is also the
lowest possible frequency, and is called the __________________________________________.
42. What is a partial or overtone?
43. Usually, several wavelengths are superimposed on each other, creating a ________________ wave.
This is what determines the quality of a sound and is how we recognize different sounds.
44. How does pipe length and pitch relate to each other?
45. Where do your vocal sounds start?
46. Where to waves go next?
47. Notice the waves coming out of the mouth are different from the waves bouncing around inside
the head. Explain how this change happens.
Go to the Sound ppt on Shmaefsky’s site and watch https://www.youtube.com/watch?v=0FoA1bBM10M and
https://www.youtube.com/watch?v=KZ7intMz2Y4 to learn about fundamental frequencies and harmonics.
Answer #48 - 54.
48. What is meant by fixed end/closed tube vs loose end/open tube?
49. What is a fundamental frequency?
50. What is a harmonic?
51. How many nodes and antinodes are in the fundamental frequency for a banjo string?
52. How many nodes and antinodes are in the fundamental frequency for a tuba?
53. What would you do to make the fundamental frequency a lower pitch for a string?
54. What would you do to make the fundamental frequency a lower pitch for a pipe?
How loud is loud? There are two ways to measure the intensity (loudness) of a sound: by its power and by the
decibel system.
Intensity = P/4πr2
P = ____________, r = ______________
A Decibel, dB, compares relative intensities of sound in a logarithmic pattern. A difference of 10dB means the
sound is twice as loud.
We hear sound when the longitudinal waves of a sound push the ear drum back and forth which makes the
anvil, the hammer, and the stirrup transfer the vibrations to the inner ear where a the vibrations in the fluid push
tiny hairs back and forth. The location of the moving hairs tells our brain what the pitch of the sound is. The
amount of pushing tells us how loud the sound is.
Go to http://www.youtube.com/watch?v=gpCquUWqaYw&feature=related. Watch the standing waves created
by sound. (2:21)
Go to http://www.youtube.com/watch?v=ynqzeIYA7Iw&feature=fvwrel. Watch the explanation. (1:58)
Go to http://www.youtube.com/watch?v=zWKiWaiM3Pw&NR=1&feature=fvwp. Watch the lesson on
resonance. (How do you like this guy? Want to visit with him?) (1:02)
Go to http://www.youtube.com/watch?v=dD9gtq08tss&NR=1. Watch the lesson on beats. (33sec)
55. Draw a graphic representation of a sound wave on the grid. Try very hard to keep the waves equal
and make your marks dark.
56. Turn your paper over. Now using the strip of transparency and a marker, do the same on that
grid.
57. Superimpose the transparency wave over the paper wave. Tape in place. Mark where the
constructive interference between the two waves is greatest. That is where you would hear a beat.
Go to http://www.youtube.com/watch?v=6jElYFYGGqg&feature=related for more hearing beats. (30sec)
Beats can overlap to form complex patterns of interference. This is what gives things their characteristic sound.
58. Chose a person to close his/her eyes. A few people take turns saying “We’re having fun learning
about sound in physics today”. As each person speaks, the listener guesses who’s talking.
59. How did the listener know who was talking?
HW Sound Problems and Sound Wave Theory Review
A Chladni plate is basically a metal plate that vibrates according to the frequency and amplitude it’s set to. This
plate gives us a way to visualize the interactions of wave interference.
Go to http://www.youtube.com/watch?v=Qf0t4/qIVWF4&feature=related to see the effects of interference
patterns. (2:13)
60. What changes as the patterns get more complex?
61. Why?