BUY THE YEAR 9 PHYSICS WORKBOOK

Sound Waves

  • Sound is a form of energy that is transferred as a wave.
  • Sound waves are mechanical waves, which means they involve the vibration of particles.
    Therefore, sound can travel through solids, liquids and gases, but cannot travel through a vacuum.
  • Sound waves are longitudinal waves, which means that sound is the result of particles vibrating back and forth – in line with the direction that the sound wave is travelling.

 
sound wave motion

Sound waves involve longitudinal particle vibrations.

(Image: © Dan Russell)

 

Generation of Sound Waves

  • Like all mechanical waves, sound waves require a source of vibration that disturbs the surrounding medium – such as air – which transfers the sound wave.
    Examples
    • Our voices are the result of vibration of our vocal cords.
    • Striking a drum generates sound by vibrating the drum skin.
    • A piano generates sound when a hammer connected to a key strikes a string.
    • A speaker generates sound due to electrical signals that cause it to vibrate back and forth.

 
speaker sound animated gif

Speakers generate sound waves by disturbing the surrounding air.

Image: © via GIPHY

 

Compressions and Rarefactions

  • Since sound waves involve the movement of particles back and forth, they result in regions where particles are closer together and regions where particles are further apart.
    For sound waves travelling through air, these are alternating regions of higher and lower air pressure.
  • The regions of higher pressure are called compressions.
    The regions of lower pressure are called rarefactions.

 
longitudinal wave compression rarefaction animated gif

Sound waves involve alternating compressions and rarefactions.

(Image: © Dan Russell)

 

(Header image: Thaut Images, Adobe Stock)