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Exploring Pitch and Volume

In this activity, students experiment with tuning forks to produce various pitches and volumes.

Tuning forks allow us to study the basic qualities of sound first hand. A tuning fork emits a pure musical tone (after waiting a moment) as it vibrates after you strike it.

There are 2 basic qualities of sound:

  • Pitch (high & low)
  • Volume (loud & soft)

Pitch is related to frequency. Changing the number of vibrations per second changes the pitch. The pitch that a particular tuning fork generates depends on the length of its prongs. Each fork is stamped with the note it produces (e.g. A) and its frequency in Hertz (e.g. 440 Hz). Shorter prongs produce higher pitch (frequency) sounds than longer prongs. Long prongs will bend more readily and therefore tend to vibrate at a lower frequency when struck.

Volume, or loudness, is related to the strength, intensity, pressure, or power of the sound. Bigger/ amplified vibrations result in bigger/louder sounds. There are a few ways of varying the volume of a tuning fork.

Hitting the fork harder will produce a louder sound because the initial vibration was larger.

Touching the vibrating fork to a table after being struck produces a louder sound. When both the table and the tuning fork vibrate, more air molecules are moved than by the tuning fork on its own.

Placing the vibrating fork on a resonance box focuses the sound and makes it echo rather than letting the sound wave/vibrations spread out, resulting in a louder sound.

Touching a vibrating fork to clothes or your hand causes a damping effect on the vibrations (reduction in size) and the sound disappears. The energy from the vibrating fork is converted to moving your skin or clothes rather than moving air.

Both pitch and volume are subjective. These words refer to what the listener experiences.

Resonance is the tendency of an object to vibrate at maximum amplitude (size) at a certain frequency. This frequency is known as the object's resonant frequency. Acoustic (sound) resonance is an important consideration for instrument builders, as most acoustic instruments use resonators (think of the box of a guitar or a violin, or the hollow body of a drum).

Objectives

  • Describe the properties of sound.

  • Describe what pitch is and how it varies.

  • Describe what volume is.

Materials

  • Per Class:
    tuning forks
    rubber mallet or the rubber bottom of a shoe
    resonance box (optional)

    If using this as an activity, provide the materials above for each pair of students.

Key Questions

  • Why do different sized tuning forks produce different sounds?
  • If you know frequency of each fork, can you tell me how many times per second each fork will vibrate?
  • How can we increase the volume of a tuning fork?
  • How can we decrease the volume of a tuning fork?

What To Do

  1. Show the class a selection of different tuning forks.
  2. Ask the class to predict which fork will have the highest and lowest sound (pitch).
  3. Strike the forks one at a time to determine the answer.
  4. Brainstorm with the class on how the tuning fork could make a louder sound.
  5. Strike the fork with more force.
  6. Strike the fork and place the handle on the table.
  7. Optional (if you have a resonance box): Strike the fork and place the handle on the box.
  8. Brainstorm with the class on how the tuning fork could make a softer sound.
  9. Strike the fork and place it on your hand and/or clothes.

Extensions

  • Get the students to touch various objects with their tuning fork to see whether the sound becomes louder or softer.
  • How do instrument builders decide the shape, size, and material of their instruments?
  • You can model how the length of a tuning fork affects the frequency by placing a plastic ruler over the edge of a table. ”Twang” the free end of the ruler while you hold the other end down on the desk. Try it with a shorter length. What do you notice?