TITLE:  Properties of Sound
Presented to grade level 5
 

GOALS
Properties of Sound is designed to teach the various characteristics of sound (frequency, pitch, loudness, wavelength, and period), show how sound travels, provide visual aids to learning about sound, and provide interesting examples of sound detection in the natural world.
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SPECIFIC OBJECTIVES

• Students will learn that sounds are caused by vibrations and travel in waves.
• Students will learn that the different characteristics of sound waves provide the variation among different sounds.
• Students will learn vocabulary terms, such as vibration, compression, rarefaction, sound wave, frequency, pitch, wavelength, and amplitude.
• Students will learn how the frequency of a sound affects the sound's pitch and period by observing the differences in low and high pitches on a guitar.
• Students will learn that sound travels fastest through solids and slowest through gasses due to the spacing of molecules and to the way in which sound waves propagate.
• Students will observe the differences in how fast sound travels through air versus a solid medium.
• Students will learn how humans employ SONAR as a detection system and how bats use echolocation in a similar way.

BACKGROUND
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SOLs COVERED

SOL 5.6

The students will demonstrate the ability of sound to travel through solids, liquids, and gasses and be able to describe the wave nature of sound.

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DEMONSTRATIONS AND EXHIBITS
Materials needed:  12" ruler, guitar or other stringed instrument, slinky

1. Show students that sound is caused by vibrations. (Also see interactive exercise.)

• Hold a ruler on end of table and pull hanging edge down and release to produce a vibrating sound.
• Pluck a guitar string and show that the string vibrates as the sound is issued.

Show compression and rarefaction in longitudinal waves with a slinky.

Explain that waves need to bounce off of molecules to move so molecules that are closer together will make a wave move more quickly. Therefore, sound will move fastest through solids, slowest through gasses, and at an intermediate speed through liquids. (Also see interactive exercises.)

Show an overhead of a sound wave and explain what the terms wavelength, period, and frequency represent on the wave.

Graphically show on an overhead what differences in amplitude and pitch would look like.

Relate the above terms to each other. For example, a high pitch is indicative of a high frequency and a long period.

• Show how pitch, frequency, and period are related on a guitar. The lower pitched strings will have a lower frequency. This can be seen on the guitar because the higher pitched string will vibrate much more quickly.
• The guitar can also be used to get students to understand amplitude differences.

INTERACTIVE EXERCISES
Materials needed:  plastic cup, rubber band, coat hanger, string

1. Sound waves vibrate.

• Have students feel the vibrations in their larynxes as they speak, hum, or sing.

• Take a plastic cup and place a rubber band around it. Place the open end of the cup up to a child's ear and pluck the band. Compare the magnified sound to the sound made by the rubber band when the cup is not up to their ear.
• Tie two pieces of string about 18" in length to the corners of a coat hanger. Have a student press the ends of the strings to their ears so that the hanger hangs away from their body. Pluck the hanger. Ask the students to compare that sound to the sound of the hanger being plucked when the strings are not up to their ears.

INTERESTING EXAMPLES
SONAR and Echolocation are examples of specialized sound detection systems.

• SONAR stands for SOund NAvigation Ranging. Boats use ultrasonic transmitters and receivers to determine what is in the water around them. They send out pulses of sound and wait to receive the reflected sound. From the reflected sound waves the receiver can give a picture of what is beneath them. SONAR is used by the fishing industry to find out where the fish are, by ships to detect the presence of submarines, and by all boats to determine the depth of the water.
• Echolocation is a system used by bats and many insects with visual obstacles to navigate their environment. Bats send out high frequency sound waves, and their modified auditory system detects echoes as they return. Bats use their ears to "see" in the dark when they are active and looking for food.

OTHER RESOURCES
 

Literature	VanCleave, Janice.  1991.  Physics for Every Kid.  John Wiley and Sons, NY.
Local Places to Visit
Related Web Sites	The Soundry (ThinkQuest '98)

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