Main Idea

All movement produces sound waves but not all sounds can be heard with the human ear.

Background

Did you ever notice that you cannot hear some sounds? Have you ever heard a group of neighbourhood dogs barking, and when you listen for what they are barking at, there is nothing to be heard? That is because the sound is inaudible to the human ear. If the pitch of a sound has either a very high or very low frequency, we may not be able to hear it. Dogs, dolphins and bats hear higher-frequency sounds than we can. The same vibrations that cause sound waves can sometimes be felt as well as heard. Deaf people can sense this movement to feel what their ears cannot hear.

Learning Objectives

• Recognize that not all sounds are audible to human ears.
• Know the meanings of audible, inaudible, and frequency.
• Understand the relationship between a sound’s audibility and its frequency.
• Identify the difference between frequency and volume.

Time

1 & 1/2 hours, including time for aesthetic design

Introducing the Concept

Present the students with a piece of sheet metal (or a sturdy piece of cardboard paper) and a piece of fabric, each of equal size and shape. Refer back to the drum activity and remind students of the various sounds the different skins made. Sometimes, it was very difficult to hear the drum noise (possibly because of the type of skin or how tightly it was secured to the drum). Keep in mind that the looser or more flexible an object, the slower it vibrates. The slower it vibrates, the lower the frequency, and the lower the pitch it will produce.

Holding the corner of the paper, wiggle it, and ask the students to determine if the sound was audible or inaudible. Next, wiggle the fabric. Be sure to wiggle them both with the same amount of force. Ask if the students can explain why one was audible and the other not. Introduce the idea of frequency and its relation to audibility. Remind students about the relationship between vibration, speed and pitch. Discuss the relationship between frequency and pitch.

Materials

• old tennis racket without strings, an empty box or an old picture frame
• nylon fishing line, twine, string, wire

Hands-On

Guitars can be made with a simple frame and string. Using the materials provided, construct a guitar. Be sure to make it pleasing to the eyes, as well as the ears. Once you have designed it, test it to see that all of the strings vibrate with an audible frequency.

1. If you are using an old tennis racket, string the nylon thread through six holes at the top and bottom of the racket. Use a variety of strings.
2. If you are using an empty box, poke six holes through each end of the box. String the thread through the holes and tie a knot at each end to secure it.
3. If you are using a picture frame, tie the strings at either end or make holes in the frame and thread your strings through.
4. Pluck the strings and listen to the sounds each makes. Try tightening the strings by repositioning the knots. Pluck the strings again to see if the sound changes.

Minds-On

• Can you produce a variety of pitches/frequencies by plucking the different strings? Are they all audible? If not, what can you do to make them audible?
• How fast are the strings vibrating? Is there a difference between the vibration speed of the different types of string? What might cause this?
• When you tighten and loosen the strings, do you hear a different sound?
• What happens when you press on one of the strings with one finger and pluck it with another?
• What force are you using to make the strings vibrate?

Teaching Tips

• Try to find a variety of “guitar” frames for this activity. The sturdiness and size will have an impact on audibility and frequency.
• If students make many different types of guitars, you may want to have them compare their findings with one another.

Interconnections

There are a variety of stringed instruments you can introduce to the students. The harp is an example of a multi-stringed instrument. As an add-on activity, you can explore other instruments or even invent your own.

If you know someone who plays guitar or another stringed instrument, you may want to invite them to the class so they can play a tune for the students. First, have the guest tune the guitar, to demonstrate how tightening or loosening the strings affects the pitch. Ask the guitarist to demonstrate how a tuning fork or digital tuner is used to easily adjust the pitch. Have the students discuss how they imagine these tuning tools work. Ask your guest to demonstrate the different sounds made by both strumming and picking the strings. If your guest has an electric guitar, a second extension activity could lead into a lesson on electricity and its applications.

Sounds Like Science - Drums

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Sounds Like Science - Bottle Organ

Sounds Like Science - Jamboree

This activity copied from APASE of Vancouver, Canada, which has regrettably disappeared from the Web.

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