Sound Waves: Characteristics and Applications · Lesson 1 of 14
Production of Sound
“Sound begins with vibration—from rubber bands and tuning forks to vocal cords and musical instruments.”
• Explain how vibrating objects produce sound. • Define vibration and source of sound. • Identify vibrating parts in different musical instruments. • Explain sound production by vocal cords. • Describe how a tuning fork demonstrates vibration.
Sound surrounds us constantly: voices, birds, thunder, music, bells and moving vehicles all create different listening experiences. Although these sounds are very different, the chapter begins by looking for one common feature in the way they are produced.
Production of Sound
Activity: Exploring a Vibrating Rubber Band
Stretch a rubber band across an open cardboard box and pluck it. While the band is moving rapidly to and fro, a sound is heard. Watch carefully as the motion gradually becomes smaller. When the rubber band finally stops vibrating, the sound also stops. Repeating the activity with greater or smaller tension changes the vibration and changes the sound.
If the rubber band is removed from the box, stretched between two fingers and plucked near the ear, it still produces sound but is usually less loud. The box helps the vibrations interact with a larger volume of surrounding air.
A periodic to-and-fro motion, or oscillation, of an object about its position of rest.
The object or vibrating system that produces sound.
A stretched string can vibrate when plucked, a metal object can vibrate when struck, and the air column inside a bansuri can vibrate when air is blown through it. Musical instruments may use vibrating strings, membranes, air columns or combinations of several vibrating parts.
Sound Production in Humans and Animals
While speaking or singing, place your fingers lightly on your throat. Vibrations can be felt because sound in humans is produced by the vibration of the vocal cords. These are tightly stretched muscular flaps located in the larynx, or voice box. The tongue, lips, mouth and nasal cavity then help shape the sound into speech or music.
Some animals use other body structures. Grasshoppers and crickets, for example, can produce sound by rubbing body parts such as wings or legs.
Tuning Fork
A U-shaped metal instrument, usually made of steel or aluminium, with two prongs or tines and a stem. It is commonly used in experiments with sound.
When a tuning fork is struck gently on a soft rubber pad, its prongs vibrate. Bringing the vibrating fork near the ear produces sound. Touching one vibrating prong gently to the surface of water creates visible ripples, providing direct evidence that the prong is moving.
Activity: Exploring a Tuning Fork
Hold a tuning fork by its stem, strike a prong gently on a rubber pad and listen. Then touch the vibrating prong to water. The water disturbance makes the otherwise rapid vibration easier to observe.
The central relationship is simple but fundamental: vibration at the source produces sound. When the source stops vibrating, it stops producing that sound.
Quiz
Which description best matches Vibration?
Which description best matches Source of Sound?
Which term matches this description: A periodic to-and-fro motion, or oscillation, of an object about its position of rest.
Which term matches this description: The object or vibrating system that produces sound.
Which statement is a key takeaway from this lesson?
Practice Problems
- Explain what happens to the sound when a plucked rubber band stops vibrating.
- Identify the vibrating part in a string instrument, a drum and a bansuri.
- Why does touching a vibrating tuning fork to water help demonstrate vibration?
- Describe how the vocal cords and mouth structures work together in speech.
Key Takeaways
• Sound is produced when an object vibrates. • A vibrating object causes nearby particles of the surrounding medium to vibrate as well. • Examples include tuning forks, stretched strings, membranes and human vocal cords. • Without vibration, a sound-producing source cannot generate a sound wave.
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Propagation of Sound