What is sound?

• Sound


  Small rapid movements (changes, fluctuations) of the atmospheric air pressure that surrounds us
• Sound can also be transmitted through other media, such as water, so not all sound consists of fluctuations in air pressure
• Sound is reflected when it meets a boundary in the medium it is travelling
• The amount of sound that is reflected and the amount that travels into the new medium depends on the medium in question and the composition of the sound
• Fluctuations in air pressure

  Caused by air molecules bunching together or becoming more widely separated
• The fluctuations in air pressure spread outwards from the source through the surrounding air, becoming gradually weaker and eventually dying away completely
• Pressure variations


  Act on the listener's hearing system, causing the eardrum to move in sympathy with the source of the pressure variations
• Sound needs a medium through which to travel - air molecules in this case
• If there are no molecules (i.e. there is a vacuum), pressure waves cannot be set up and so sound cannot travel
• Sound waves


  Cycles of pressure variations that vary in a repeating pattern
• Sound waves


  • They may only last for a very short time, as in the case of a short sound such as a rifle shot
  • They may last for a long time, as in the case of continuing sound such as a person singing a long note
• Pressure wave


  A regular pattern of high- and low-pressure regions
• A travelling wave is a way of transmitting energy
• Typical waveforms


  • Tuning fork
  • Clarinet
  • Dropped plate