Norwood Science Center

Transcription

1 Norwood Science Center Energy Grade 5 Background Information: The sense of hearing involves the ear, the auditory nerve, and a special center within the brain. We hear because our ears respond to vibrations in the air. The important parts involved in hearing are protected inside the skull. The outer "ear" that we see plays only a small part in hearing. Its funnel-shape picks up sound waves and helps direct them to the ear canal. At the inner end of the ear canal is a thin membrane called the eardrum. As sound waves strike this tight, flexible membrane, they cause the eardrum to vibrate. The eardrum passes on the vibration to three tiny bones: the hammer, anvil, and stirrup. These three bones carry the vibrations to the inner ear. The inner ear is composed of the cochlea and the semicircular canals. The semicircular canal in the inner ear is the sense organ for balance. The sound waves exert pressure on fluid in the cochlea where the fluid's movement is detected by the auditory nerve endings. Electrical impulses are set up in the auditory nerve and sent to the brain where they are identified as sounds. Behind the eardrum is the Eustachian Tube, which connects the middle ear to the throat. Its purpose is to equalize the air pressure on both sides of the eardrum. Our brain uses the electrical impulses for locating the direction from which a sound comes. A sound will always reach one ear a fraction of a second sooner than the other. The brain is able to interpret this minute difference. To a certain degree, we also can detect the distance a sound is from us. Because our ears are separated by several inches, the brain is able to compute an approximate distance. Scientists use a triangulation to mathematically calculate distances when using sonar, echolocation and other listening devices. Tuning Forks Gr. 5 Page 1 of 5

2 Tuning forks are keyed to a certain pitch. This depends on their thickness and length, and the material of which they are made. Most tuning forks vibrate so rapidly that it is difficult to detect movement. When the tines of a vibrating fork are lowered slowly into a dish of water, the water will splash, demonstrating that vibrations are occurring. When the handle of a vibrating fork is place on a table or desk, the sound will be amplified. If the tuning fork is touched to a large paper cup, a shoebox, or the body of a stringed instrument, the sound should be amplified. Take home points: A lighter object will vibrate faster, have a higher pitch. A tighter object will vibrate faster, have a higher pitch. Sound travels better through liquid, best through a solid. TITLE: TUNING FORKS PURPOSE: Observe and describe the function of the ear. Detect vibrations as a sound is produced. Detect movement of sound from one solid to another. MATERIALS: (per pair) Tuning fork Table tennis ball Ear Diagrams (2) 30 cm (12") string Tape PROCEDURE: 01. Discuss why ears are important. (They allow us to hear and communicate. The ear is sensitive to a wide range of sounds - high, low, loud, and soft.) Tuning Forks Gr. 5 Page 2 of 5

3 02. Distribute the diagram of the ear. Discuss with students the different parts of the ear: outer ear, eardrum, middle ear with chain of three bones, and the inner ear with the cochlea. Fill in blanks. 03. Sound is vibration. We live in a world of vibrations. Have the class sit quietly for five minutes. No talking allowed! a. Write down all the sounds they hear. b. Name what's making the sound. c. Describe the sound they hear. d. Try to figure out what might have been vibrating to make the sound. 04. Distribute tuning forks. Instruct students to hold the handle of the tuning fork and strike it on the bottom of their shoe. Bring the double end near your ear. Ask students to describe what happens. 05. Tape one end of the string to the table tennis ball. Hold the string so that the ball is suspended freely. Strike the tuning fork again and listen to the sound. When the sound just disappears, touch the suspended ball with the tuning fork. Make sure the fork tines are horizontal as seen below. Tuning Forks Gr. 5 Page 3 of 5

4 Ask students the following: a. What happens when the tuning fork touches the ball? b. Why does this happen? c. Remember, you no longer hear the sound. Was the tuning fork still vibrating? Why don't you hear any sound? 06. Strike the tuning fork and place the handle on your desk. Do not touch the vibrating tines. See the figure below. Put your hand on your desk. Do you feel anything? Put your ear on your desk. a. Does sound appear to be coming from the desk? b. What do vibrations of the tuning fork do to the desk? c. If the wood of the desk is to give off sound, what must it do? 07. Ask students the following: a. When the tuning fork no longer vibrates, do you hear any sound? b. What must the tuning fork do to produce sound? Tuning Forks Gr. 5 Page 4 of 5

5 CONCLUSIONS: 01. Although sound is not heard, the table tennis ball was forced away from the tuning fork, indicating that the tuning fork was still vibrating. Vibrations must be strong to be heard. Vibrations not ordinarily heard with the unaided ear are often amplified to be carried to our ears. 02. The vibrations of the tuning fork are transmitted to the wood. The wood vibrates and in turn sets up sound waves, which reach our ears. 03. The tuning fork is a specialized instrument that vibrates at a specific number of vibrations per second to produce a specific tone. This is called frequency. The vibrations are demonstrated by water being pushed aside in the container when the vibrating fork is immersed in it. EXTENSIONS: Big Ears: Have students listen to a tape or CD. Begin with the volume off, slowly turn the volume higher and have the students raise their hands when they are able to hear the music. When all hands are raised, slowly turn the volume down until only a few hands are still up. Tell the class that there is another way to "turn the volume up." Show them how to make "big ears" by putting their hands behind their ears with their palms facing outward. Have them make big ears and compare the number of students who can hear the music. Set the volume of the player so that all students can hear. Have them listen, alternatively with their "big ears" off and on. Ask them to describe the difference in the sound. They should notice that by making their outer ear "larger", they are able to "catch" more sound. Ask students, What do your hands catch when you make "Big Ears?" (sound vibrations) Why do some animals (rabbits and elephants) need to have big ears? (their eyesight is poor so they rely on their keen hearing). SOURCES: 01. Physical Science Activities for Grades 2-8. Tolman and Morton, Science Curriculum Activities Library, Basic Science Inquiry Kit: Sound. Dr. B. Syrocki, W. Costello, AIMS Education Foundation, Primarily Physics, Tuning Forks Gr. 5 Page 5 of 5