Topic Sound Key Question How do our ears allow us to hear sounds? Focus The children will be able to explain that the ear is the organ of the body that receives sound. Guiding Documents Project 2061 Benchmarks • People can often learn about things around them by just observing those things carefully, but some­ times they can learn more by doing something to things and noting what happens. • People use their senses to find out about their sur­ roundings and themselves. Different senses give different information. Sometimes a person can get different information about the same thing by moving closer to it or further away from it. Science Physical science sound Life science hearing Integrated Processes Observing Communicating Predicting Drawing conclusions Materials Paper to make a megaphone Background Information We hear because our ears respond to vibrations in the air. The important parts involved in hearing are pro­ tected inside the skull. The outer ear that we see plays only a small part in hearing. Its shape helps direct air vibrations into the ear canal. The air vibrations hit the eardrum ­ a flexible membrane inside the ear canal ­and cause it to vibrate. The vibrating eardrum causes movement in three tiny bones (the hammer, anvil and 27
PRIMARILY PHYSICS stirrup) in a chamber called the middle ear. Then the vibration is sent on into the inner ear. The inner ear is composed of the cochlea and the semicircular canals. The sound waves exert pressure on fluid in the cochlea where the fluid's movement is detected by the tiny hairs connected to the auditory nerve. Electrical impulses travel up the auditory nerve to the brain where they are identified as sounds. Behind the eardrum is a tube, the eustachian tube, which connects the middle ear to the throat. Its purpose is to equalize the air pressure on both sides of the ear drum.
The semicircular canal in the inner ear is the sense organ for balance. Management CACJTION the students that loud sounds and sharp ob­ jects can damage the ear. Procedure 1. 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.) 2. Discuss with the students the different parts of the ear (see Background Information). [The outer ear (the part we see) and the ear drum, the middle ear with the chain of three bones, and the inner ear with the cochlea.] 3. Have the students fill in the blanks with the names for the parts of the ear on the My Ear activity sheet. 4. Have the students listen to the sounds from a tape or record. 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. 5. 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 com­ pare the number of students who can hear the music. 6. Set the volume of the tape so that all students can hear. Have them listen, alternately with their "big ears" off and on. Ask them to describe the differ­ ence in the sound. They should notice that by making their outer ear "larger," they are able to "catch" more sound and it sounds differently. 1994 AIMS Education Foundation 7. Explain that the ear can pick up very soft sounds and is very sensitive. Loud sounds with much energy can cause pain and damage to the ear. The hammer, anvil, and stirrup respond much less efficiently to loud sounds (they slip) protecting the delicate hair cells of the inner ear. Discussion 1. What do your hands catch when you make "big ears?" [sound vibrations] 2. Why do some animals (rabbits and elephants) need to have big ears? [Their eyesight is poor, so they rely on their keen hearing.] Extensions 1. Make two megaphones. Have the students go out on the baseball diamond with one standing on home plate and the other standing on the pitcher's mound. Ask them to talk to each other (without yelling) with the megaphones. Does the sound carry? Megaphones permit sound to go out only in one direction. Thus energy is concentrated rather than being dissipated over a wide space. 2. Discuss noise pollution. Ask the class how loud noises make them feel. For example, can they work well when the class is noisy? Does a loud motor­ cycle sound bother them? 3. Take a listening walk. The children can apply the "big ears" technique to help them hear. Prepare the children to listen to sounds during their walk. Take a small tape recorder along. Back in the classroom, discuss what they heard and what made those sounds. Categorize the sounds into loud, soft; high, low; near, far; people, animals, weather; if they liked or disliked the sounds, etc. PRIMARILY PHYSICS 28 1994 AIMS Education Foundation