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Sunday, December 2, 2012

Making Waves with Sound

I remember the first time I taught sound, I repeatedly found references to making a crude drum to demonstrate vibrations. There is so much more to do. The following are my favorites to do when studying sound.

Feel the Vibration.

Give all the students a balloon. Give them time to blow up the balloon and tie the ends. Have students hold the balloons by their fingertips. Read a poem or other short text. Vary your speech from soft to loud and back to soft. I would read the children's book, "Moses Goes to a Concert" by Isaac Millman. Let students share what they felt.

A percussionist, Evelyn Glynnie who is profoundly deaf has played for the London Symphonic orchestra  She experiences music through its vibration.

It's important that students know that there are three types of waves.

Sound is a mechanical wave which must have matter to travel. The moon has about 25 moonquakes a month. If there were matter between the Earth and Moon, the Moon would ring like a bell.

Sound travels faster through a solid than a liquid or gas.

In Westerns, on television, the cowpoke and native americans put their ear to the ground to hear horse hoofs and people in the distance. Wyatt Earp the legendary lawman had terrible arthritis and joint problems from laying on a
ground at night.

There are two ways to demonstrate this.
1. Tie a length of string to a spoon. Give students different lengths of string or instruct them to cut different lengths. I used yarn but twine will do.
2. Have students wrap the free end of yarn around a finger and insert the finger into the ear. Actually touching the concha of the external inner ear with the finger.
Diagram of external ear: Use figure 904 for reference.
3. Standing and Bending from waist with the finger wrapped by the string and touching the interior of the external ear, have students allow the spoon to tap against a chair, desk or other inanimate object. They should hear a very loud sound.
4. Have students remove string and finger from ear and allow the spoon to tap against the same object.
5. Ask question, Does sound travel better through the air or the string and your finger?
(Children will want to say, the air) Prompt them, where was the sound louder? When your finger was touching your ear or not touching your ear? When they tell you when the finger was touching your ear, repeat the question, does sound travel better through the air or the string and your finger and more of them will get the answer correct which is your finger and string.
6. Lead students to the conclusion that sound travels better through a solid which is your finger and a string.

The second way to demonstrate this is tying two strings to a metal coat hanger. A plastic coated coated metal hanger will work. This time they will put both index fingers wrapped with a separate string in their ears.

The benefit of the spoon is you can do the next experiment with the spoons.
Have students wrap the string attached to the spoon around their index finger and touch their finger to the interior of their external ear. Listen to the sound.
Try a spoon with a different length of string.
Does it have a higher or lower pitch?
Short string will have a higher pitch than a longer string.
Take time to discuss the difference between Pitch and Loudness.

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