Sound Waves: Vibrations, Energy, and the Art of Hearing

Everyday we hear sounds from various sources like humans, birds, bells, machines, vehicles, televisions, radios etc. Sound is a form of energy which produces a sensation of hearing in our ears. Sound is produced by vibrating objects. When an object vibrates, it creates a disturbance in the surrounding air molecules, generating a sound wave.

Production of Sound: Vibrations, Waves, and the Human Voice

• Production of Sound: Sound is produced by striking the tuning fork, by plucking, scratching, rubbing, blowing or shaking different objects. 
  • We set the objects vibrating and produce sound. 
• Meaning: Vibration means a kind of rapid to and for motion of an object. 
• Sound Production in Human: The sound of the human voice is produced due to vibrations in the vocal cords. 
  • Sound is produced by the vibration of objects. 
• Wave Propagation: When an object vibrates, it creates a disturbance in the surrounding medium (usually air) which propagates in the form of waves, ultimately reaching our ears.

Production of Sound by Humans: The Role of the Voice Box and Vocal Cords

• In humans, the sound is produced by the voice box or the larynx. 
  • Voice box in humans  is at the upper end of the windpipe. 
  • Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. 
• When the lungs force air through the slit, the vocal cords vibrate, producing sound. 
  • When the vocal cords are tight and thin, the type or quality of voice is different  from that when they are loose and thick.

Propagation of Sound: Vibrations, Mediums, and Wave Dynamics

• Sound is produced by vibrating objects. 
• Required Medium: The matter or substance through which sound is transmitted is called a medium. 
  • It can be solid, liquid or gas. 
  • Sound moves through a medium from the point of generation to the listener.
• When an object vibrates, it sets the particles of the medium around it vibrating. 
  • The particles do not travel all the way from the vibrating object to the ear. 
  • A particle of the medium in contact with the vibrating object is first displaced from its equilibrium position. 
  • It then exerts a force on the adjacent particle. 
  • As a result, the adjacent particle gets displaced from its position of rest.
• After displacing the adjacent particle, the first particle comes back to its original position. 
  • This process continues in the medium till the sound reaches your ear. 
  • The disturbance created by a source of sound in the medium travels through the medium.
• Wave: It is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion.
• Mechanical Wave: Sound waves are characterised by the motion of particles in the medium and are called mechanical waves. 
  • Air is the most common medium through which sound travels. 

• Compression: When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called a compression (C).
  • This compression starts to move away from the vibrating object.
• Refraction: When the vibrating object moves backwards, it creates a region of low pressure called rarefaction (R) . 
• As the object moves back and forth rapidly, a series of compressions and rarefactions is created in the air. 
• These make the sound wave that propagates through the medium.

Sound Waves are Longitudinal waves: Longitudinal Motion and Wave Nature

• Longitudinal Waves: In a longitudinal wave, the particles of the medium (such as air, water, or solids) vibrate in the direction of the wave’s propagation. 
  • This means that the motion of the particles is parallel to the direction of the wave itself.
  • In the case of sound waves, air molecules move back and forth parallel to the direction in which the sound is travelling. 
  • The compressions and rarefactions alternate, creating a series of high-pressure (compression) and low-pressure (rarefaction) regions.
• Transverse Waves: In a transverse wave, the particles of the medium oscillate perpendicular to the direction of the wave’s motion. 
• This creates crests (high points) and troughs (low points) in the wave.
  • Examples of transverse waves include light waves and waves on a string. 
  • In light waves, the electric and magnetic fields oscillate perpendicular to the direction of propagation.
• Nature of Waves: While sound waves are longitudinal, some waves in other mediums (like water waves on the surface of a pond) can exhibit both longitudinal and transverse characteristics. 
• Surface Waves: These are known as surface waves, as they have components that move both parallel and perpendicular to the direction of wave motion. 
• Longitudinal Wave Only: Sound waves specifically, which travel through air or other mediums, are longitudinal waves and do not exhibit transverse motion.