Elisabet O. Orville
The first WRITING ASSIGNMENTS will again be group activities to develop a vocabulary of hearing.
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1. Have the whole class sit as quietly as possible for a few minutes. Then in their notebooks list all the sounds they are hearing. WRITE their words on the board. Add other words for sounds (such as crash, rustle, murmur)
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Are there as many synonyms for
listening
as there are for
seeing
? List as many as possible.
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2. Survival in the desert at night if you are a small rodent depends on how acute your sense of hearing is. Kangaroo rats, which are common in our western deserts, are the favorite food of predators such as snakes, lizards, hawks, owls, foxes and bobcats.
The Life Nature Library Book of the Desert
has excellent desert scenes, pages 79-93. In the daytime kangaroo rats sleep in their burrows but at night when it cools off they energy looking for seeds which they stuff into their cheek pouches. However, the predators are also out at night so the survival of the rat depends on its keen hearing and its ability to jump out of the way.
Have your students WRITE a story about the night of a kangaroo rat—all the sounds he hears, which ones mean danger and which ones don’t. Make it as dramatic as possible.
What is sound?
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1. ACTIVITY. (you will need a tuning fork and rulers)
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Strike the prongs of a tuning fork against a desk and then hold it upright on the desk so that students can feel the vibrations. A tuning fork that sounds the A above the middle C on the piano is vibrating 440 times a second. This is its
frequency
. The greater the frequency, the higher the the pitch of the sound.
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____
____
Have students hold rulers against their desks with different lengths protruding and make them vibrate. A short end vibrates with a higher pitch than a long section. They can also feel their larynxes vibrate when they talk.
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2. ACTIVITY. Have your students construct a
bar graph
showing the upper frequency of sound that various animals can detect. (elephants 12,000 waves/second; humans 20,000; bats 150,000; moths 150,000; dogs 44,000; rats 72,000; frogs 10,000; porpoises 150,000; crocodiles 6000; cats 65,000). If they are artistically inclined they can put a simple figure of each animal below the bar representing it.
Which animals can detect ultrasound? (higher frequencies than humans can detect)
Structure and function of the ear:
Diagram 4 at the end of the unit is a picture of the human ear. Xerox it and have students tape it into their notebooks. Divide the ear into the Outer ear, Middle ear and Inner ear and then write in the functions of each part. A good source of large diagrams is the
Life Science Library Book of Sound and Hearing
. pages 38-51.
Outer ear
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A. pinna—Helps concentrate sound waves.
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B. auditory canal—Brings the sound waves to the eardrum.
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Middle ear
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C. eardrum—magnifies the vibrations and passes them on to the ossicles.
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D. ossicles—Three tiny connected bones that magnify the vibrations and pass them on to the cochlea.
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Inner ear
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E. semicircular canals—Help you to maintain your balance.
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F. cochlea—A tiny coiled snail-like organ filled with fluid which vibrates. Connected to the auditory nerve.
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G. auditory nerve—Changes the vibrations into electric impulses which are sent to the brain
WRITING ASSIGNMENT: Explain all the things that happen to the sound waves from the time your friend asks you a question to the instant that your brain perceives the answer.
Echolocation in bats :
Bats are the only mammals that can fly; they are also totally nocturnal. Flying in the dark and catching insects on the wing has helped them evolve a special sense called echolocation. The bat has an enormous larynx which emits beams of very high frequency sound (up to 150,000 cycles/second). These beams (which we can’t hear of course) bounce off obstacles and flying insects alike and the echoes return to the bat’s huge ears. The obstacles are avoided and the moths are pursued, usually successfully. Interestingly enough, some moths have also developed ultrasound signals which they use to detect the presence of bats. It is almost like an arms race.
There are some excellent large photographs of bats in the
Life Nature Book of Animal Behavior
, pages 22-23, 106, 116-117.
WRITING ASSIGNMENT: Imagine that you are a bat hanging upside down by your claws in a cave. It is night and you are just waking up. You are very hungry. Describe what the next few hours will be like for you, catching moths and mosquitoes by echolocation. (also avoiding crashing into trees and rocks in the dark). Use your imagination.
Medical Ultrasound:
Although we humans can’t echolocate in the dark, we have developed some instruments which emit beams of high frequency sound almost like bats. This ultrasound technology can tell us what is inside our bodies. It is especially popular in certain obstetrical situations; when the doctor suspects multiple births, breech birth or simply needs to know the due date of the mother. Ultrasound is painless and appears to be harmless, unlike X-rays.
A probe which emits ultrasound with a frequency of millions of cycles per second is moved over the abdomen of the pregnant woman. The same probe also records the reflected echoes from the fetus which are then changed to visible light signals on a screen. Often these days, a mother is carrying a picture of her baby in her wallet even before he is born!
WRITING ASSIGNMENT: In the learning package that accompanies this unit there is an article from the New Haven Register which tells exactly how ultrasound aided in the pregnancy of one young woman in New Haven. Read it out loud together (there are several technical terms in it) and then have the students WRITE on the following questions.
a. Explain the procedure when you have ultrasound.
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b. Why did Mrs. Carbone have the first ultrasound?
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c. Why did her doctor ask her to have a second one?
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d. What are some of the other reasons why pregnant women have ultrasound?
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e. In what ways is medical ultrasound like echolocation in a bat?
What is it like to be deaf?
We all know people who are hard of hearing and who are leading normal lives, but what is it like to live in a world of total silence? There is another article in the learning package from the New Haven Register which describes a 20 year old local woman who has been deaf from infancy. Again have your students read the accompanying article. Discuss her feelings and adjustments to her handicap and then WRITE on the following questions.
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a. Why do you think Jackie says that she would prefer being deaf to being blind or crippled?
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b. What are some of the ways in which hearing people react to deaf people?
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c. Jackie can’t hear doorbells, alarm clocks or telephones, but she can see them. Explain.
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d. What is Jackie’s job? Is it a good one for a deaf person? Think of some other professions suited for deaf people. Think of some that would not be good.