Vibration and Source of Sound

Introduction

In the previous topic, we learnt that sound is produced by vibrating objects. Whenever we hear a sound, there is always some object or part of an object that is vibrating.

For example, the string of a guitar, the membrane of a drum, the metal body of a bell, the air column inside a flute, and the vocal cords in our throat vibrate to produce sound.

Vibration

Vibration is the periodic to and fro motion of an object about its mean position.

Vibration = Periodic to and fro motion

When an object vibrates, it moves repeatedly on both sides of its normal or mean position. This motion produces sound.

Example of Vibration

When a stretched rubber band is plucked, it starts moving rapidly to and fro. This rapid motion is called vibration.

As long as the rubber band vibrates, sound is produced. When the rubber band stops vibrating, the sound also stops.

Figure

Vibration Produces Sound Mean position To and fro motion Sound waves Vibrating string String moves about its mean position

Explanation

The above figure shows a vibrating string. The dotted line represents the mean position of the string. When the string is plucked, it moves to and fro about this mean position.

This repeated to and fro motion is called vibration. Due to these vibrations, sound waves are produced and travel through the surrounding medium.

Mean Position

The mean position is the normal or central position of a vibrating object when it is at rest.

During vibration, the object moves on both sides of this mean position.

Source of Sound

The object that produces sound is called the source of sound.

Source of sound = Object that produces sound

Every sound has a source. The source may be a string, membrane, air column, metal body, vocal cord, or any other vibrating object.

Examples of Sources of Sound

Sound Producing Object Source of Sound Vibrating Part
Guitar Guitar string String
Drum Drum membrane Stretched membrane
Flute Air inside flute Air column
Bell Bell body Metal body
Human voice Voice box Vocal cords
Whistle Air inside whistle Air column

Different Vibrating Parts That Produce Sound

1. Vibrating Strings

In some musical instruments, stretched strings vibrate and produce sound.

  • Guitar
  • Sitar
  • Violin
  • Rubber band

2. Vibrating Membranes

In drums and similar instruments, a stretched membrane vibrates and produces sound.

  • Drum
  • Tabla
  • Dholak

3. Vibrating Air Columns

In wind instruments, the air column inside the instrument vibrates and produces sound.

  • Flute
  • Whistle
  • Shehnai

4. Vibrating Metal Bodies

Some metal objects produce sound when they vibrate after being struck.

  • Bell
  • Metal plate
  • Tuning fork

5. Vibrating Vocal Cords

In humans, sound is produced by the vibration of vocal cords present inside the voice box or larynx.

When we speak or sing, our vocal cords vibrate and produce sound. The tongue, lips, mouth, and nasal cavity help convert this sound into speech or music.

How Animals Produce Sound

Many animals also produce sound by vibrating body parts.

  • Humans produce sound by vibrating vocal cords.
  • Birds produce sound using their sound-producing organs.
  • Grasshoppers and crickets produce sound by rubbing their wings or legs.
  • Some animals produce sound by striking or rubbing certain body parts.

Important Relation Between Vibration and Sound

Vibration and sound are closely related. If vibration is present, sound can be produced. If vibration stops, sound also stops.

Vibration present → Sound produced

Vibration stops → Sound stops

Examples from Daily Life

  • When a school bell rings, its metal body vibrates and produces sound.
  • When we pluck a guitar string, the string vibrates and produces sound.
  • When a drum is beaten, its membrane vibrates and produces sound.
  • When we speak, our vocal cords vibrate and produce sound.
  • When air is blown into a flute, the air column inside it vibrates and produces sound.
  • When a tuning fork is struck, its prongs vibrate and produce sound.

Important Points

  • Sound is produced by vibrating objects.
  • Vibration is the periodic to and fro motion of an object about its mean position.
  • The mean position is the normal position of an object when it is at rest.
  • The object that produces sound is called the source of sound.
  • Every sound has a vibrating source.
  • Sound may be produced by vibrating strings, membranes, air columns, metal bodies, or vocal cords.
  • When vibration stops, sound also stops.
  • In humans, sound is produced by vibrating vocal cords.
  • In many musical instruments, more than one part may vibrate to produce sound.

Conclusion

Vibration is the basic cause of sound production. When an object vibrates, it produces sound. The object that produces sound is called the source of sound. Different sources of sound have different vibrating parts, such as strings, membranes, air columns, metal bodies, and vocal cords. Therefore, to understand sound properly, it is necessary to understand vibration and the source of sound.

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