LEARN NC

2.6 How does an animal's environment affect the frequency of its sound?

By Debra Hall and Crystal Patillo

Provided by Kenan Fellows Program.

Animals use songs and sounds to communicate. Some of these sounds are produced within human auditory range, which for most of us is between 20 and 20,000 vibrations per second (20 HZ–20kHZ).

Sound that is lower than 20 vibrations is called infrasound. These are sounds that we cannot hear, but can be seen on a spectrogram. Thunderstorms and earthquakes produce sounds that are in the infrasound ranges. Elephants communicate with infrasound. This allows them to communicate with each other over very long distances.

Some animals produce sounds that have more than 20,000 vibrations per second. These are called ultrasounds. Bats use ultrasound to communicate and find insects to eat. A bat will produce a high-pitched squeak and the echoes of the ultrasound wave will bounce off of the insect indicating its position to the hungry bat.

The human ear can recognize single sine waves because sounds with such a waveform sound “clean” or “clear” to humans. Some sounds that approximate a pure sine wave are whistling, a crystal glass made to vibrate by running a wet finger around its rim, and the sound created by a tuning fork. To the human ear, a sound that is made up of more than one sine wave will either sound “noisy” or will have detectable harmonics.

Learning outcomes

The learner will infer that vibrations are needed to make sound. They will demonstrate how low-pitched sounds have slower vibrations and high-pitched sounds have faster vibrations.

Teacher planning

Time required

One 60-minute period

Materials needed

  • bat and elephant pictures and spectrograms
  • textbook
  • tape
  • 30-centimeter wood rulers
  • soft-tip mallets
  • small bells, finger cymbals, or choir chimes

Technology resources

Free Raven Lite software from the Cornell Lab of Ornithology. You can use this software to record, save, and visualize sounds as spectrograms and waveforms.

Activities

This lesson uses the 5E instructional model, which includes five phases: engage, explore, explain, elaborate, and evaluate.

Engage

Show students a dog whistle. Blow the whistle and ask students if they know what is special about dog ears. Discuss how dogs can hear things that we are unable to hear with our human ears. Tell students that they will be investigating how to alter sounds.

Explore

Give each pair of students a ruler, some tape, and a text book. Ask students how we can make sounds with the ruler. Have students work in groups to develop strategies for making sound. If they are having difficulty, demonstrate to students how to place the ruler flat on the table, cover the end of the ruler with a book, and pluck the end that is hanging off the table. The ruler will vibrate causing sound. Have students test different lengths of the ruler and listen to each sound. Ask students to fill in a data table similar to the one below about the sounds they produce and hear.

Example

Animal sound data table
Length off table Observations Pitch
5 cm Ruler is difficult to pluck, vibrates quickly High
10 cm
15 cm
20 cm Ruler vibrates slowly Low

Explain

Discuss the data collected. The higher sounds were created when the length of the ruler hanging off the table was shorter. The lower sounds were created when the length of the ruler was longer. Explain how we can hear the different pitches because our ears are sensitive to a certain range. Inform students that the dog whistle was not within human hearing range and ask what this tells us about animal hearing. Have students discuss how certain animals hear things that humans cannot.

Elaborate

Examine pictures of a bat and an elephant. Using the introductory information at the beginning of this lesson, discuss what types of sounds and pitches the two animals create. Ask students what we could use to detect sounds that were out of our range. Review the spectrograms that the students used in previous lessons or that you created using the Raven Lite software. Ask students how spectrograms help us to see the sound. Show students two spectrograms, one of a bat and one of an elephant. Discuss the frequency of each animal. Students should infer that the bats have a higher frequency (ultrasound) and the elephants have a lower frequency (infrasound). Ask students how this works to suit each animal’s environment.

Draw two sine waves on the board similar to those in the diagram below but without labels. Ask students what they notice about the lines. Accept all responses. Discuss how there are more peaks in the top picture and they are closer together. Discuss how the bottom line has the same height but that there are fewer peaks and the distance between them is longer. Discuss the lines as waves and have students do the wave.

wavelength diagram

Connect the high and low frequencies of the bat and elephant with distance. Establish how low frequencies travel farther than high frequencies. Allow students to demonstrate by striking soft-tip mallets on their desks to replicate the sounds of an elephant. Contrast this low-frequency sound with the high-frequency sounds of small bells, finger cymbals, or choir chimes.

At this point, explore how the musical instruments from cultures around the world and from various times in history were created to function in a particular environment. Explain that cultural communities choose materials available from their habitat. Both human and animal communicators utilize materials that produce pleasing sounds. A cockatoo uses a twig to beat on a log. If the cockatoo likes the sound of that twig it will save the twig. Many human musicians favor a particular instrument over another. A concert pianist will choose a grand piano over a console piano. Allow students to explore instrumentation from various international cultures.

Evaluate

Students should be evaluated based on their data tables.

Critical vocabulary

frequency
the number of waves produced per second, which is the same as the number of vibrations produced per second
pitch
the highness or lowness of a tone, as determined by the frequency of vibrations per second
infrasound
sound with a frequency too low to be heard by the human ear
ultrasound
acoustic energy in the form of waves having a frequency above the human hearing range

North Carolina curriculum alignment

Music Education (2001)

Grade 4

  • Goal 8: The learner will understand relationships between music, the other arts, and content areas outside the arts.
    • Objective 8.01: Identify similarities and differences in the meanings of common terms used in dance, music, theatre arts, and visual arts including line, color, texture, form/shape, rhythm, pattern, mood/emotion, theme, and purpose.
    • Objective 8.02: Identify ways in which the principles and subject matter of other content areas taught in the school are related to those of music.

Grade 5

  • Goal 8: The learner will understand relationships between music, the other arts, and content areas outside the arts.
    • Objective 8.01: Identify similarities and differences in the meanings of common terms used in dance, music, theatre arts, and visual arts including line, color, texture, form/shape, rhythm, pattern, mood/emotion, theme, and purpose.
    • Objective 8.02: Identify ways in which the principles and subject matter of other content areas taught in the school are related to those of music.

National Standards

In addition to meeting objectives of the North Carolina Standard Course of Study, this lesson plan addresses the following national standards.

Content Standard A: Abilities necessary to do scientific inquiry

  • Understanding about scientific inquiry.
  • Employ simple equipment and tools to gather data and extend the senses.

Content Standard B: Physical Science

  • Position and motion of objects
  • Sound is produced by vibrating objects. The pitch of the sound can be varied by changing the rate of vibration.

Content Standard C: Life Science

  • The characteristics of organisms
  • Organisms and their environments

Content Standard E: Science and Technology

  • Abilities of technological design
  • Understanding about science and technology
  • Abilities to distinguish between natural objects and objects made by humans.

Content Standard F: Science in Personal and Social Perspectives

  • Characteristics and changes in populations
  • Science and technology in local challenges