sound waves

• Sound is caused by the vibration of particles but not all vibrations can be heard as sound
• Common ideas about sound come from the limited range of vibrations that human ears can detect
• Sound waves


  Longitudinal waves that cause particles to vibrate parallel to the direction of wave travel
• Sound waves can travel through solids, liquids or gases
• Speed of sound


  Depends on the medium through which it is travelling
• In air, the speed of sound is about 330 metres per second
• Sound cannot travel through a vacuum because there are no particles to carry the vibrations
• How the human ear detects sound

  1. Sound waves enter the ear canal

  2. Cause the eardrum to vibrate

  3. Three small bones transmit vibrations to the cochlea

  4. Produces electrical signals

  5. Pass through the auditory nerve to the brain
• Frequency of a sound wave

  Related to the pitch that is heard: high frequency sound waves are high pitched, low frequency sound waves are low pitched
• Amplitude of a sound wave


  Related to the volume of the sound: high amplitude sound waves are loud, low amplitude sound waves are quiet
• The cochlea is only stimulated by a limited range of frequencies, so humans can only hear certain frequencies
• The range of normal human hearing is 20 Hertz (Hz) to 20,000 Hz (20 kHz)
• Sound is caused by the vibration of particles but not all vibrations can be heard as sound
• Common ideas about sound come from the limited range of vibrations that human ears can detect
• Ultrasound


  Sound with a frequency greater than 20,000 Hz (20 kHz)
• Ultrasound waves have a frequency higher than the upper limit for human hearing - above 20,000 Hertz (Hz)
• Different species of animal have different hearing ranges
• A dog can hear the ultrasound produced by a dog whistle but humans cannot
• Uses of ultrasound


  • Breaking kidney stones
  • Cleaning jewellery
• Ultrasound imaging


  Creates a picture of something that cannot be seen directly, such as an unborn baby in the womb, or faults and defects inside manufactured parts
• What happens when ultrasound waves meet the boundary between two different materials

  1. Some of the ultrasound waves are reflected at the boundary

  2. The time taken for the waves to leave a source and return to a detector is measured

  3. The depth of the boundary can be determined using the speed of sound in the material and the time taken
• Echo sounding


  High frequency sound waves can be used to detect objects in deep water and to measure water depth
• The time between a pulse of sound being transmitted and detected and the speed of sound in water can be used to calculate the distance of the reflecting surface or object
• Echo sounding is applied in sonar systems used to find shipwrecks, submarines and shoals of fish
• Bats and dolphins use a similar method called 'echolocation' to detect their surroundings and to find food
• Seismic waves


  Shock waves travelling through the Earth, usually caused by an earthquake
• Seismic waves


  • Can cause damage to structures on the Earth's surface
  • Can cause tsunamis
• 1. waves


  Longitudinal waves
• 1. waves


  Transverse waves
• Properties of seismic waves

  • P-waves are longitudinal, faster, can travel through solids and liquids
  • S-waves are transverse, slower, can only travel through solids
• Seismic waves from large earthquakes are detected around the world
• Seismic waves are curved as the waves refract due to the gradually changing density of the layers
• 1. waves are not detected on the opposite side of the Earth, suggesting the mantle has solid properties but the outer core must be liquid
• 1. waves are detected on the opposite side of the Earth, and refractions between layers cause two shadow zones where no P-waves are detected
• The size and positions of these shadow zones indicate there is a solid inner core