Physics

• Sound

  All sounds are caused by vibrating sources
• Production of sound by vibrating sources

  Vibrating source caused the air around them to vibrate
• String instruments

  • They are plucked or bowed to vibrate
  • The length of the string can be changed and this changes the note produced
  • The body of the instrument and the air inside it also vibrate and this give the instrument its distinctive sound
• Oud and violin playing the same note

  They sound very different
• Wind instruments

  • They are blown to cause the column of air inside to vibrate
  • Players cover and uncover holes to change the length of air column
  • This changes the pitch of the note
• Sound waves are longitudinal waves
• Compression

  A region in the sound wave where the particles are close to each other
• Rarefaction

  A region in the sound wave where the particles are further apart
• Sound can travel through any kind of matter, but not through a vacuum
• Sound waves are mechanical waves
• Sound travels fastest in solids and slowest in gases
• Audible range of sounds

  20 Hz to 20 000 Hz
• The speed of sound in air is approximately 330–350 m/s
• Measuring the speed of sound

  1. Need a source of sound and two detectors in line with the sound

  2. Measure the distance between the two detectors and the time interval between the sound reaching them

  3. Then use (speed = distance/time) to calculate the speed of sound
• Echo

  The reflection of sound waves
• Ultrasound

  Sound with a frequency higher than 20 kHz
• Uses of ultrasound

  • Non-destructive testing of materials
  • Medical scanning of soft tissue
  • Sonar including calculation of depth or distance from time and wave speed
• Greater amplitude of a sound

  The louder it is
• Greater frequency of a sound

  The higher the pitch is
• The audible range of sounds decreases with age
• Ultrasound applications

  • Non-destructive testing of materials
  • Medical scanning of soft tissue
  • Sonar including calculation of depth or distance from time and wave speed