Sound Waves (AQA GCSE Physics)

• Sound waves are vibrations of air molecules
• When a sound wave comes into contact with a solid those vibrations can be transferred to the solid
  • For example, sound waves can cause a drinking glass to vibrate
  • If the glass vibrates too much the movement causes the glass to shatter

• Sound is an example of a longitudinal wave, hence it consists of:
  • Compressions - regions of higher density
  • Rarefactions - regions of lower density

Sound is a longitudinal wave consisting of compressions and rarefactions - these are areas where the pressure of the air varies with the wave

• These compressions and rarefactions cause changes in pressure, which vary in time with the wave
  • Therefore, sound is a type of pressure wave

• When the waves hit a solid, the variations in pressure cause the surface of the solid to vibrate in sync with the sound wave

When sound waves hit a solid, the fluctuating pressure causes the solid to vibrate

• Sound waves can be heard by human beings because sound waves are transferred from the air to the solid components of the ear
• In the case of the human ear, the sound waves are transferred by two main solid components:
  • The eardrum which is made of tissue and skin
  • Three small bones

• The sound wave travels down the auditory canal towards the eardrum
  • The pressure variations created by the sound wave exert a varying force on the eardrum causing it to vibrate
  • The vibration pattern of the sound waves creates the same pattern of vibration in the eardrum

• The eardrum vibration is transferred to the three small bones
• The vibration of these small bones then transfers the vibrations to the inner ear
  • In the inner ear, nerve cells detect the sound and send a message to the brain giving the sensation of sound

The human ear is made up of several components which turn sound waves into signals which the brain can interpret

• The transmission of sound to the human ear only works over a limited range of frequencies
  • This limits the range of sound frequencies a human can hear

• The range of frequencies a human can hear is 20 Hz to 20 000 Hz